JPH0346101A - Thermomagnetic recording method and thermomagnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the performance to protect recorded information by successively forming a 1st magnetic layer and a 2nd magnetic layer on a substrate and forming the 2nd magnetic layer to have the coercive force higher than the coercive force of the 1st magnetic layer. CONSTITUTION:This recording medium has the 1st and 2nd magnetic layers 111, 112 successively on the nonmagnetic substrate 110 and is formed with the 2nd magnetic layer 112 so as to have the coercive force at ordinary temp. higher than the coercive force at ordinary temp. of the 1st magnetic layer 111. The coercive force at ordinary temp. of the 2nd magnetic layer 112 is preferably >=2000Oe and the coercive force at 150 deg.C is preferably <=150Oe. The coercive force at ordinary temp. of the 1st magnetic layer 111 is lower than the coercive force of the 2nd magnetic layer 112 and is satisfactory if the value thereof is, for example, about 500 to 2000Oe; for example, ordinary magnetic powder for magnetic recording, such as magnetite, is used. The Curie point of the 2nd magnetic layer 112 is preferably about 90 to 160 deg.C and the Curie point of the 1st magnetic layer 111 is preferably above the Curie point of the 2nd magnetic layer 112 and >=300 deg.C.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention provides high-density recording by providing a second magnetic layer containing magnetic powder with a low Curie point and high coercive force on an ordinary magnetic recording layer. The present invention relates to a thermomagnetic recording medium with improved characteristics and improved protection performance of the recorded state due to the shielding effect of high coercive force, and a recording method for such a thermomagnetic recording medium.

<Prior Art> When recording audio or video, it is generally necessary to record various signal components ranging from long wavelengths to short wavelengths. In this case, it is well known that the shorter the wavelength, that is, the higher the recording density, the more the signal recorded on the magnetic layer is recorded only in a very shallow region on the surface of the magnetic layer.

On the other hand, it is known that the long wavelength component recording region becomes deeper from the surface if the magnetic layer is sufficiently thick.

In this way, the recording area in the magnetic layer depends on the wavelength of the recording signal, so the magnetic layer has a double layer structure, and the surface area of the medium near the magnetic head (called the upper layer) is specially designed to improve short wavelength characteristics. Many technologies have been proposed.

For example, in order to reduce the 'ti magnetic loss associated with shorter wavelengths, there is a method of making the coercive force of the upper layer larger than that of the magnetic layer below it (referred to as the lower layer), and further reducing the thickness of the upper layer. A method of making it thinner (for example, Japanese Patent Application Laid-Open No. 54-2130)
Publication No. 48, Publication No. 54-143113, Publication No. 58-1
No. 7539, No. 61-165820, No. 62
(Japanese Patent Publication No. 78718, Japanese Patent Publication No. 37-2218, Japanese Patent Publication No. 39-23678, Japanese Patent Publication No. 52-28364, etc.) In addition, in order to effectively utilize the perpendicular magnetization component, which increases as the wavelength becomes shorter, magnetization of the upper layer is facilitated. A method of spatially equalizing the axis distribution or a method of perpendicular orientation (Japanese Unexamined Patent Publication No. 62-43833, Japanese Patent Publication No. 40-5351, etc.) Furthermore, barium ferrite is a magnetic material suitable for these orientations. Examples include methods using fine particles (Japanese Unexamined Patent Publication No. 57-195329, Japanese Patent Application Laid-open No. 58-119610, etc.).

<Problems to be Solved by the Invention> On the other hand, with the trend toward higher density audio and video recording, a method for reliably recording signals with shorter wavelengths is required.

However, in magnetic recording systems using conventional magnetic recording media, the effects of recording demagnetization and self-demagnetization are large, and there are limits to the improvement of short wavelength recording characteristics.

Among these, recording demagnetization is a phenomenon in which recording is performed while the recording medium moves relative to the recording head, so the recorded area is demagnetized under the influence of the polarity reversal of the head as it moves away. is a phenomenon in which the magnetization of the magnetic layer that carries the recording signal is demagnetized by the influence of the demagnetizing field within the magnetic layer. It is known that all of these problems become more pronounced as the recording wavelength becomes shorter.

These losses due to demagnetization occur because the coercive force of the recording medium becomes relatively small with respect to the demagnetizing field, which increases as the wavelength becomes shorter. Therefore, this can be reduced by increasing the coercive force of the medium.
However, in the conventional magnetic recording system, since the writing and erasing capabilities of the magnetic head are limited, it is impossible to increase the coercive force of the medium infinitely, and it is difficult to use a coercive force of 2000 Oe or more. Therefore, it is thought that the coercive force of the upper layer of a double-layer magnetic recording medium can be increased to a maximum of about 2000 Oe, and there is a limit to the improvement of short wavelength characteristics in this respect.

Furthermore, it is well known that in double layer media, if the coercive force difference between the lower layer and the upper layer is too large, the sagging phenomenon will become noticeable in the intermediate frequency band, and this will not lead to uniform improvement of characteristics over the entire frequency band ( Japanese Patent Publication No. 58-159
No. 238, No. 61-168126, No. 62-
78718).

Therefore, if the overall balance is taken into account, it may not be possible to increase the coercive force unnecessarily just for the purpose of improving short wavelength characteristics.

On the other hand, from the perspective of preserving recording against external disturbance magnetic fields, the strength of the magnetic field generated near magnets used in daily life can generally reach nearly 2000 Oe, so as mentioned above, the coercive force of the medium is Below 2000 Oe, the recorded signal is altered due to the proximity of these magnets, etc.
There were fears that it would be further destroyed.

The present invention was made under these circumstances, and provides a thermomagnetic recording device that can perform both short-wavelength recording and long-wavelength recording well, has high protection performance for recorded information, and is easy to record. It is an object of the present invention to provide a medium and a recording method for such a thermomagnetic recording medium.

Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (8).

(1) A method for performing magnetic recording on a magnetic recording medium having a first Mi layer and a second magnetic layer sequentially on a nonmagnetic substrate, wherein the coercive force of the second magnetic layer at room temperature is the same as that of the 161st layer at room temperature. higher than the coercive force, and the Curie point of the second magnetic layer is 2.
00° C. or lower, heating the second magnetic layer to reduce its coercive force, recording mainly short wavelength components in the 21a magnetic layer with reduced coercive force,
A thermomagnetic recording method characterized in that long wavelength components are mainly recorded in the first magnetic layer.

(2) The thermomagnetic recording method according to (1) above, wherein the coercive force of the second magnetic layer is greater than or equal to the coercive force of the first magnetic layer during recording.

(3) The thermomagnetic recording method according to (1) above, wherein the short wavelength component is recorded on the heated second magnetic layer, and the long wavelength component is recorded on the eleventh ifi layer at room temperature.

(4) A thermomagnetic recording medium having a first magnetic layer and a second magnetic layer sequentially on a substrate, wherein the second ia layer has a higher coercive force at room temperature than the first magnetic layer at room temperature,
A thermomagnetic recording medium characterized in that the Curie point of the second magnetic layer is 200° C. or less, short wavelength components are mainly recorded in the second magnetic layer, and long wavelength components are mainly recorded in the first magnetic layer.

(5) The coercive force of the second magnetic layer is 2000O at room temperature.
The thermomagnetic recording medium according to (4) above, which has a temperature higher than e and 200 Oe or less at 150°C.

(6) The thermomagnetic recording medium according to (4) or (5) above, wherein the thickness of the second magnetic layer is equal to or less than the thickness of the first magnetic layer.

(7) Any of the above (4) to 6), wherein the second magnetic layer contains ferromagnetic ultrafine particles containing a Fe2P type hexagonal crystal structure mainly composed of Fe, Co, and P and a binder. The thermomagnetic recording medium described in .

(8) 21st i! The thermomagnetic recording medium according to any one of (4) to 7) above, wherein the magnetic layer is magnetically perpendicularly oriented.

<Function> The thermomagnetic recording medium of the present invention has a first magnetic layer and a second magnetic layer sequentially on a substrate, and the coercive force of the second magnetic layer is higher than the coercive force of the first magnetic layer. . The long wavelength components are mainly recorded in the first magnetic layer, and the short wavelength components are mainly recorded in the second magnetic layer.

In the present invention, when recording on such a second magnetic layer, the second magnetic layer is heated by a heating means to reduce its coercive force to within the range of writing and erasing capabilities of the magnetic head.

In this case, heating may be performed by directly heating the recorded portion, or heating and recording may be performed at different times.

In any case, by adjusting the temperature of the recording portion of the second magnetic layer to an arbitrary temperature above room temperature, the coercive force of the second magnetic layer can be set to an arbitrary value during recording.

In this case, setting the coercive force of the second magnetic layer to be as large as possible within the writing capability of the magnetic head is effective in improving short wavelength characteristics. In addition, if recording is performed by adjusting the coercive force so that the relationship between the coercive force and the force of the first m-layer is optimized, it is possible to record in the medium wavelength region, which is a problem in magnetic recording media having two magnetic layers. It is also possible to solve the sagging phenomenon.

Since the temperature of the second FIIIi layer quickly returns to room temperature after recording, the coercive force of the second magnetic layer increases rapidly accordingly. This reduces recording demagnetization and self-demagnetization, and since the second magnetic layer has an extremely large coercive force at room temperature, it has a shielding effect against external disturbing magnetic fields, and the security of recorded information is maintained.

Specific composition> Hereinafter, the specific configuration of the present invention will be explained in detail.

The thermomagnetic recording medium of the present invention has a first magnetic layer and a second magnetic layer sequentially on a substrate, and the second magnetic layer has a higher coercive force at room temperature than the first magnetic layer at room temperature. .

The coercive force of the second magnetic layer at room temperature is not particularly limited and may be set to an appropriate value depending on the intended recording wavelength, external magnetic field strength to be protected, etc., but it is preferably 2000 Oe or more. If the coercive force at room temperature is less than the above, recorded information is likely to be disturbed by external magnetic fields, and self-demagnetization becomes a problem. Although there is no upper limit to the coercive force at room temperature, when ferromagnetic ultrafine particles as described below are used as a magnetic material, it is difficult to obtain a coercive force exceeding 5000 Oe.

Further, the coercive force of the second magnetic layer at 150°C is 200
Oe or less, particularly preferably 150 Oe or less. If the coercive force at 150° C. exceeds the above range, it will be difficult to reduce the coercive force to an appropriate value during recording.

The coercive force of the 16th magnetic layer at room temperature is lower than the coercive force of the second magnetic layer at room temperature, and is not particularly limited as long as it is within the writing capability of the magnetic head used. Therefore, it may be set to an appropriate value depending on the intended recording wavelength, for example, about 500 to 2000'Oe.

Such a first magnetic layer contains magnetic powder for ordinary magnetic recording, such as acicular particles of magnetite or oxides containing magnetite or cobalt, and acicular particles mainly composed of metallic iron. Barium ferrite hexagonal particles may be used.

The Curie point of the second magnetic layer is 80 to 200°C, especially 90°C.
The temperature is preferably about -160°C. If the Curie point is less than the above range, the magnetic thermal stability of the second m layer is insufficient, and if it exceeds the above range, the second m layer will have insufficient magnetic thermal stability.
It becomes difficult to reduce the coercive force of the magnetic layer to a level suitable for recording.

Note that the Curie point of the first magnetic layer may be equal to or higher than the Curie point of the second magnetic layer, but when recording short wavelength signals and long wavelength signals separately as described later, the Curie point must be 300° C. or higher. is preferred.

In these magnetic layers, it is preferable to make the second magnetic layer as thin as possible so that the characteristics of the first magnetic layer can be brought out.

Specifically, the thickness of the second magnetic layer is 0.1-1-1, especially 0.
．． It is preferable that it is 2-0.84. If the thickness of the second magnetic layer is less than this range, the amount of magnetization will be small and the short wavelength characteristics will be deteriorated. Moreover, when this range is exceeded, the long wavelength characteristics deteriorate.

Although there is no particular restriction on the thickness of the first magnetic layer, it is preferably about 1 to 6 μm.

The thermomagnetic recording medium of the present invention is produced by kneading a magnetic material, a binder, and various additives, and applying the mixture onto a nonmagnetic substrate.
This is a so-called coating type medium in which a magnetic layer and a second magnetic layer are formed.

Although there is no particular restriction on the magnetic material contained in the second Fli layer, it is preferable to use ferromagnetic ultrafine particles containing Fe, Co, and P as main components because the above characteristics can be easily obtained. It is preferable to configure the second magnetic layer by dispersing such ferromagnetic ultrafine particles in a binder.

Such ferromagnetic ultrafine particles (hereinafter abbreviated as ultrafine particles) usually have a hexagonal Fez P structure as a main body.

The content of these elements in the ultrafine particles is preferably within the following range.

F e / Co = 95 / 5 ~ 70 / 30
, more preferably F e /Co = 90 / l
It is O~80/20.

If the content of Co relative to Fe is less than the above range, the Curie temperature will drop significantly and the coercive force at room temperature will drop to about 500 Oe or less. Also,
If the above range is exceeded, the magnetocrystalline anisotropy decreases, so that the coercive force also decreases to about 500 Oe or less.

On the other hand, (Fe + Co) / P = 85 /
15 to 60/40, more preferably (Fe+C
o) / P = 80 / 20 ~ 65 / 35
It is.

When the content of P in Fe+Co is less than the above range, the effect of P that contributes to increasing the magnetocrystalline anisotropy decreases,
The coercive force becomes about 500 Oe or less.

For the stoichiometric hexagonal Fe2P structure, the theoretical P
The amount is approximately 33%. It is generally considered that a Fe 2 P structure is not formed when the P content is 30% or less, but if produced by the manufacturing method described below, 1
A hexagonal Few P structure can be formed in the range of up to 5%.

The reason for this is thought to be that since fine particles are synthesized by rapid cooling from a high-temperature gaseous state by the method described below, the hexagonal crystal structure, which is stable at high temperatures, is frozen as is. When the amount of P is less than the stoichiometric composition, the lattice points of P are considered to be vacancies as they are, or other elements added in the raw materials or during the reaction process, such as C%N, SL, Sn, B, Ni, Zn, Ti%Mn, A
A structure in which l1, Cr, etc. are substituted at the P position is also conceivable.

In addition, if the amount of P exceeds the stoichiometric composition, the amount of P in the ultrafine particles will be excessive, but if it is at least within the above range,
No change was observed in the line diffraction image, and no adverse effects occurred on the magnetic properties. However, when Pfi exceeds the above range, the saturation magnetization decreases to 35 emu/g or less, which is not preferable.

Such ultrafine particles may contain C in addition to the main components Fe, Co and P.

C is incorporated into the ultrafine particles from the raw material powder, reactor constituent materials, or atmosphere within the reactor, which will be described later, and is thought to have a stabilizing effect on the hexagonal F 192 P structure.

More specifically, the inclusion of C is effective in reducing the electrical resistance and improving the dispersibility of ultrafine particles.

Further, the presence of C during the reaction is effective in effectively reducing and evaporating the raw material when it is an oxide.

Thereby, the raw material oxide can be reduced and phosphorized using only nitrogen gas without using dangerous hydrogen.

Further, C has the effect of preventing ultrafine particles from being fused together and forming a chain shape during generation of ultrafine particles, and improving corrosion resistance.

When C is contained, the content of C in the ultrafine particles is preferably 20 wt% or less, more preferably 0.1 to 10 wt%. If the content of C is less than the above range, the effect of containing it will be insufficient,
If it exceeds the above range, the saturation magnetization will decrease.

In the ultrafine particles, most of Fe, Co and P are
Forms a hexagonal F e a P structure.

Therefore, ultrafine particles with high coercive force and low Curie temperature are realized. The existence of the hexagonal Fe2P structure can be confirmed by X-ray diffraction.

It should be noted that, in addition to the hexagonal Fe and P structures, some Fe3P structures or aFe structures may be present in the ultrafine particles as long as the magnetic properties are not affected.

The composition of such ultrafine particles can be determined by plasma emission spectroscopy, C,
H,N elemental analyzer, fluorescence X 1. ! It can be measured by analysis, other chemical analysis, etc.

In addition to the above-mentioned elements, the ultrafine particles may contain additional elements such as N, Si, Sn, B, Ni, Zn, Ti,
Mn, AI2, Cr, etc. may be contained.

The ultrafine particles produced by the method described below are spherical particles, and this appearance can be confirmed using a transmission electron microscope or the like.

The average particle size of such ultrafine particles is preferably 0.00
5 to 0.1 μm, more preferably 0.01-0
．． 05pm.

If the average particle size is less than the above range, the supernormal particles will exhibit markedly sexual behavior and the coercive force will decrease significantly. Moreover, if it exceeds the above range, the agglomeration effect between the particles becomes large and it becomes difficult to loosen the particles, which is not preferable.

According to the manufacturing method described below, ultrafine particles having such an average particle size can be obtained as a single, substantially spherical particle without the need for pulverization or other means. Therefore, highly dispersible ferromagnetic ultrafine particles can be easily realized.

The ultrafine particles obtained by the manufacturing method described below have a coercive force of 500 Oe or more, particularly 800 Oe or more, and even 200 Oe or more.
Since it can be greater than 0 Oe, especially 2100 to 5000 Oe, it is suitable for the above-mentioned thermomagnetic recording medium.

In addition, the saturation magnetization is 35 emu/g or more, especially 50 emu/g.
~80 emu/g.

In addition, the Curie temperature of such ultrafine particles is 80 to 2
00℃, especially 90~! Since the temperature can be set at 60° C., it is suitable for the thermomagnetic recording medium of the present invention.

According to the production method described below, ultrafine particles based on hexagonal Fe and P structures can be produced in all of the composition ranges of Fe, Co and P as described above.
Mainly, the coercive force and Curie temperature can be freely controlled within the above ranges depending on the purpose.

Next, a method for manufacturing such ultrafine particles will be explained.

Such ultrafine particles are preferably produced by a gas phase reaction method.

As the gas phase reaction method, it is preferable to use a method in which raw material powder containing at least Fe and Co is evaporated in a gas phase and then rapidly cooled to obtain ultrafine particles.

In the raw material powder, Fe and Co may be contained alone or in the form of compounds such as oxides, phosphides, or phosphates. Also,
A mixture of these may be used.

There is no particular restriction on the type of compound used, but Fe and C
O oxide, iron phosphate, etc. can be suitably used.

P may be contained in the raw material powder, or may be contained in the gas phase.

When P is contained in the raw material powder, it may be contained alone in the same way as above, or it may be contained in the form of a compound. Alternatively, a mixture of these may be used.

Although there is no particular restriction on the type of compound used, particularly preferably used P compounds include ammonium phosphate, iron phosphate, cobalt phosphate, and sulfur oxide.

Containing P in the gas phase can be realized, for example, by introducing hydrogen phosphide gas such as phosphine, which serves as a P supply source, into the reaction system.

In order to contain C in the ultrafine particles, it is necessary to add C to the raw material powder.
may be contained or may be contained in the gas phase. Alternatively, it can also be supplied from reactor constituent materials used in manufacturing.

When supplying from raw material powder, carbon black or the like may be used as the C source.

When supplying from the gas phase, as a C source, CO1, various hydrocarbons, carbonyl compounds, etc. may be included in the carrier gas that transports the raw material.

In addition to these elements, the raw material powder may contain, as additives, the above-mentioned additional elements, alloys or compounds thereof, or mixtures thereof.

Each of the above-mentioned elements and these additives may be contained in the raw material powder so as to have a desired content when formed into ultrafine particles.

Moreover, scrap, ore, mill scale, etc. can also be used as a mixture containing each of the above-mentioned elements.

Even when such low-cost raw materials are used, substantially spherical ultrafine particles with good magnetic properties can be obtained.

The average particle diameter of the raw material particles constituting the raw material powder containing each of the above elements is preferably 100 μm or less, particularly preferably 10 μm or less.

By setting the average particle size to this level, the evaporation efficiency of Fe, Co, etc. can be increased, and the raw material particles can be easily quantitatively supplied into the reactor.

Such raw material particles can be obtained by pulverizing and mixing raw materials such as the above-mentioned elements or compounds using a known pulverizing means such as a jet mill or a ball mill.

Furthermore, in order to improve the fluidity of the raw material particles, a known binder may be used to granulate the raw material particles. In addition, it is preferable to use spray drying etc. for granulation. Although there is no particular restriction on the binder used, examples of suitable binders include polyvinyl alcohol, polyvinylpyrrolidone, and ethyl cellulose.

Next, in a reactor, the raw material particles as described above are heated in a gas phase to instantaneously evaporate the entire raw material particles, and then rapidly cooled and condensed to form ultrafine particles.

In this case, the entire reaction system is preferably carried out in an inert or reducing atmosphere at atmospheric pressure or lower.

The heating means to be used is not limited as long as it can instantaneously evaporate raw material particles, but thermal plasma, particularly plasma jet, is preferably used.

Examples of means for generating a plasma jet include:
DC plasma is an example of DC plasma, in which a direct current arc discharge is generated between the inner surface of the tip of a nozzle-shaped anode and the cathode tip provided within this anode, and plasma gas supplied into the anode is heated to an extremely high temperature. It is heated to create thermal plasma, which is ejected as a jet from a nozzle at the tip of the anode.

In addition, a plasma jet using inductively coupled plasma (hereinafter abbreviated as ICP) is also preferably used.

In this method, plasma is generated inductively by a high-frequency magnetic field generated by flowing gas into a quartz tube and passing a high-frequency current through a coil wound around the quartz tube.

By introducing raw material particles into such a plasma jet, the raw material particles are instantaneously heated and instantaneously evaporated.

FIG. 3 and FIG. 4 show a preferred example of an apparatus for producing ultrafine particles.

The reactor l shown in FIGS. 3 and 4 has an evaporation section 2, a cooling section 3, and a collection section 4 in series.

A plasma jet 211 is ejected into the furnace of the evaporation section 2 by the plasma jet generating means 21 . As the plasma jet generating means 21, a DC plasma generator is used in FIG. 3, and an ICP generator is used in FIG. 4.

Raw material powder is introduced into the plasma jet 211 by a carrier gas from the raw material powder supply means 22 .

In the case of the DC plasma shown in FIG. 3, the flow rate of the ultra-high temperature plasma gas is very fast, so the raw material powder does not reach the center of the plasma and is likely to be blown off on the outside of the fast-flowing flame. For this reason, it is better to bring the inner wall of the furnace in the evaporation section as close as possible to the plasma flame, maintain the inside of the furnace at a high temperature, and create a turbulent flow of plasma to prolong the residence time of the raw material powder under high temperature. .

For this reason, the inner wall surface of the furnace of the evaporation section 2 is covered with a heat-resistant material 23. As the material of the heat-resistant material 23, it is preferable to use graphite, boron nitride, tungsten, or other heat-resistant alloy materials. Note that when a carbon-containing material such as graphite is used as the heat-resistant material, C can be supplied to the ultrafine particles from this material.

The heat resistant material 23 is further covered with a heat insulating material 24.

Preferable materials for the heat insulating material 24 include fibrous carbon, alumina, and zirconia.

Heat is retained within the evaporation section by the heat resistant material 23 and the heat insulating material 24. In addition, in this case, the inner wall of the evaporation section 2 is
It is preferable that the temperature is maintained at a high temperature of at least 1000°C or higher.

On the other hand, in ICP, the diameter of the flame of plasma is larger than that of DC plasma, the gas flow rate is slower, and the raw material powder can be supplied from the central axis of the plasma. Residence time can be increased. Therefore, by increasing the inner wall diameter of the reactor shown in FIG. 4 and lowering the temperature of the reactor wall, it is possible to effectively advance the evaporation reaction while preventing the contamination of other substances. In this case, as shown in FIG. 4, the raw material powder supply means 22 is installed on the central axis of the plasma jet generation means 21, and the raw material can be directly conveyed to the center of the plasma jet 211.

Gas generated by evaporation of the raw material powder in the evaporation section 2 is carried to the cooling section 3 by the carrier gas.

Then, it is rapidly cooled by the cooling gas supplied from the cooling gas supply port 31 and condensed to become the target ultrafine particles 10. The obtained ultrafine particles 10 are transported to the collection section 4 by a carrier gas and discharged outside the reactor l.

The ultrafine particles obtained in this manner are free from fusion or chain formation between particles, and are monodispersed, substantially spherical particles.

Art H2, He
, N2, NHa, Co, various hydrocarbons, etc. may be appropriately selected depending on the purpose, but as the plasma gas, ArH2 mixed gas, ArNz mixed gas, NtHa mixed gas, etc. Preferably, the cooling gas is preferably H2, N2 or NH.

When the ultrafine particles contain C, an appropriate gas may be selected from these as described above.

Note that the second magnetic layer in the thermomagnetic recording medium of the present invention may contain not only ultrafine particles produced by such a method, but also ultrafine particles produced by such a method.
It goes without saying that any magnetic material can be used as long as it satisfies the above characteristics.

There are no particular restrictions on the binder in which the magnetic material is dispersed, and any binder that can withstand heating during recording may be selected from binders used in ordinary coating-type magnetic recording media.

For example, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, polyester resins, epoxy resins, phenol resins, melamine resins, polyvinylphenol resins, isocyanate compounds, etc. are preferably used. .

Such a binder is used in an amount of 100 parts by weight of the magnetic material.
It is preferably contained in an amount of about 0 to 100 parts by weight.

These magnetic materials, binders, other additives, etc. are kneaded using a suitable solvent and applied as a magnetic paint.
Usually, after applying and drying the first magnetic layer, a second magnetic layer is obtained by calendering, but it is also possible to orient the magnetic material in a magnetic field after applying each magnetic paint. For example, when performing orientation treatment using the above-mentioned ultrafine particles in the second magnetic layer, the shape of the ultrafine particles is approximately spherical, but -
Since it has axial magnetic anisotropy, magnetic field orientation is extremely easy. In this case, the squareness ratio of the second magnetic layer that has been oriented in the magnetic field is about 0.7 to 0.9 in the direction of the oriented magnetic field. The magnetic field strength in this case is 2000
~8000G is preferable.

In this way, the axis of easy magnetization of the magnetic powder in the second magnetic layer can be aligned in any direction depending on the direction of the orienting magnetic field. As the recording wavelength becomes shorter, the proportion of the perpendicular component of the magnetic flux from the magnetic head increases, so if the orientation is perpendicular to the medium, the perpendicular magnetization component in the second magnetic layer can be increased. A medium with better wavelength characteristics can be obtained.

The first magnetic layer only needs to have a coercive force lower than that of the second magnetic layer at room temperature, and there are no other restrictions on the m-type material used for the first magnetic layer as long as it satisfies these conditions.

For example, the magnetic material used for the first Mi layer includes acicular Fe3O4, γ-Fe203, or acicular oxide particles containing Co, as well as acicular particles mainly composed of metallic iron, and acicular oxide particles containing Co. Examples include hexagonal barium ferrite-based oxide particles, and a magnetic material having optimal magnetic properties depending on the purpose may be selected from these.

In addition to the above-mentioned coated media, the present invention can also be applied to media having a continuous thin film type magnetic layer made of various metals, various oxides, and the like.

There are no particular restrictions on the non-magnetic substrate on which these magnetic layers are deposited, and in addition to flexible plastic films used for ordinary magnetic tapes, floppy disks, etc., rigid substrates such as aluminum alloys and glass can be used. can.

Further, there is no particular restriction on the shape of the substrate, and the shape of a disk, tape, etc. may be selected depending on the purpose, and there are no particular restrictions on its dimensions.

In the thermomagnetic recording medium of the present invention as described above, it is preferable that the following thermomagnetic recording is performed.

FIG. 1a is an explanatory diagram of a preferred embodiment of the thermomagnetic recording method of the present invention.
11 and a second magnetic layer 112 in this order; a heating means 120 for heating the second magnetic layer; a first magnetic layer 111 and a second magnetic layer 1;
A magnetic head 130 for simultaneous recording is shown at 12, and the thermomagnetic recording medium 100 is moving in the direction of the arrow in the figure. Note that the heating means 120 shown in FIG. 1a is a laser beam irradiation device.

1b and 1c are graphs showing the temperature distribution and coercive force distribution of the second magnetic layer 112 when the thermomagnetic recording medium 100 in progress shown in FIG. 1a is continuously heated by the heating means 120. A and B in the figure respectively indicate the position of the heating means and the position of the magnetic head 130 in FIG. 1a. Furthermore, in FIG. 1c, the dotted line indicates the coercive force of the first magnetic layer 111.

When recording on the thermomagnetic recording medium 100, first, the second magnetic layer 112 is heated by the heating means 120 to reduce the coercive force of the second magnetic layer 112.

The temperature of the heated portion of the second magnetic layer 112 decreases as the medium advances, and the coercive force increases in accordance with the temperature. Then, the magnetic head 130 performs recording on the first magnetic layer 111 and the second magnetic layer 112 at the point in time when the coercive force of the second magnetic layer 112 becomes an optimum value for the writing ability of the magnetic head 13o.

In FIG. 1a, heating means 120 and magnetic head 130
By adjusting the positional relationship and/or the heating temperature, the coercive force of the second magnetic layer 112 during recording can be set to an arbitrary value. Note that the heating temperature is preferably below the Curie point of the magnetic material contained in the second magnetic layer.

For example, in the second magnetic layer containing ultrafine particles as described above, the coercive force during recording can be increased to about 500°C by changing the temperature during recording within the range of about 50°C to about 120°C.
It can be any value between e and about 2000 Oe.

Therefore, the selection range of magnetic materials used for the first magnetic layer is extremely wide, and almost all conventionally known magnetic materials can be used depending on the purpose.

In this case, the optimum coercive force of the second magnetic layer during recording is equal to or greater than the coercive force of the first magnetic layer, as shown at position B in FIG. It is about 1 to 1.5 times, especially 1.05 to 1.2 times, the coercive force of the layer. Further, in consideration of the coercive force of the magnetic material normally used for the 16th FF layer and the recording ability of the magnetic head, it is preferable that the coercive force of the second magnetic layer during recording is 2000 Oe or less.

The heating means 120 for heating the second magnetic layer 112 is not particularly limited, and heating can be performed by light irradiation using various light emitters such as a laser light emitter and an infrared light emitter.
In addition, various other heating elements can also be used.

The heating means 120 is connected to the magnetic head 13 as shown in FIG. 1a.
The magnetic head 130 may be provided at a position preceding the magnetic head 130 and heated in advance, or may be provided near the gap position of the magnetic head 130.
Heating and recording may be performed simultaneously.

In addition to these methods, heating may be performed from the nonmagnetic substrate side of the thermomagnetic recording medium.

Note that if there is a recorded track adjacent to the track on which recording is to be performed, the adjacent track will also be heated due to the heating, and there is a possibility that the recorded information in the second magnetic layer will be lost.
For this reason, it is also preferable to narrow down the spot diameter of the heating light or provide a heat shielding means to avoid heating of adjacent tracks.

During such recording, the second magnetic layer is located on the magnetic head side, so short wavelength components are recorded, and the first magnetic layer is located at a longer distance from the magnetic head than the second magnetic layer, so long wavelength components are recorded. .

The short wavelength component recorded in the second magnetic layer preferably has a wavelength of 1p or less, and the long wavelength component recorded in the 1613th magnetic layer preferably has a wavelength of 1 or more.

After recording is performed, it is preferable that the coercive force of the second magnetic layer is rapidly increased. For this purpose, it is preferable to quickly cool the second magnetic layer.

There is no particular restriction on the method of cooling the 26th layer, and in addition to natural cooling, a cooling means for actively cooling may be used.

For example, cooling can be performed by bringing it into contact with a magnetic head. In FIG. 1b, the temperature rapidly decreases at position B in contact with the magnetic head when the second magnetic layer is cooled by contact with the magnetic head.

If the coercive force of the second magnetic layer is rapidly increased after recording, the influence of recording demagnetization can be extremely reduced. Also,
After performing such thermomagnetic recording, 2
Since the coercivity returns to an extremely large coercive force exceeding 000 Oe, it is possible to suppress the self-demagnetization loss for short wavelength recording in the second magnetic layer to an extremely low level. Moreover, such a high coercive force magnetic layer also has the effect of safely protecting recorded information from the influence of external disturbing magnetic fields.

In addition to the method of simultaneously recording the short wavelength component and the long wavelength component as explained above, the present invention can also record these components separately.

For example, first, a long wavelength signal is recorded on the magnetic recording medium of the present invention. At this time, since the first m-type layer and the second magnetic layer are at room temperature, the long wavelength signal is not recorded in the second magnetic layer, but the long wavelength signal is recorded in the first magnetic layer.

Next, at least the second magnetic layer is heated to record short wavelength signals. In this case, it is preferable to heat the second magnetic layer so that the coercive force of the second magnetic layer does not become less than the coercive force of the first magnetic layer so that the magnetization of the first magnetic layer is not transferred to the second magnetic layer.

Further, in the magnetic recording medium of the present invention, a short wavelength signal can be recorded first, and then a long wavelength signal can be recorded.

In this case, at least the second magnetic layer is heated to record short wavelength signals. At this time, the short wavelength signal is mainly recorded in the second magnetic layer. Then, the long wavelength signal is recorded at room temperature. Since the second magnetic layer has an extremely large coercive force at room temperature, a long wavelength signal can be recorded only in the first Mi layer without affecting the short wavelength signal in the second Ila layer.

Furthermore, in the above-mentioned superimposed recording of a short wavelength signal and a long wavelength signal, it is also effective to use separate magnetic heads each having an optimal gap length for each recording wavelength.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Preparation of ultrafine particle sample] Iron oxide powder, cobalt oxide powder, iron phosphate powder, and carbon black were ground and mixed, and then granulated to obtain raw material particles.

The raw material powder composed of these raw material particles was put into a reactor made of graphite, evaporated by a direct current arc plasma jet, and further rapidly cooled and condensed by cooling gas to obtain ultrafine particle samples No. 1.

Another ultrafine particle sample was produced by changing the composition of the raw material particles and the manufacturing conditions.

The atomic ratios of Fe/Co and (Fe+Co)/P in the raw material particles used to prepare each sample, the C content, the plasma gas and cooling gas used, and the composition and characteristics of each ultrafine particle sample are shown in the table below. Shown in 1.

The atomic ratios of Fe/Co and (Fe+Co)/P were determined by plasma emission spectroscopy, and the C content was determined by C, H, N.
The average particle size was measured using an elemental analyzer, the average particle size was measured using a transmission electron microscope, and the crystal structure was measured using X-ray diffraction.

Moreover, the coercive force was measured by VSM with an applied magnetic field of 10 kOe.

[Preparation I of Magnetic Tape Samples] Using each of the ultrafine particle samples shown in Table 1, magnetic paints having the following compositions were prepared.

Ultrafine particles 100 parts by weight Vinyl chloride Vinyl acetate resin 17 parts by weight Urethane resin
17 parts by weight Stearic acid 2 parts by weight Toluene 80 parts by weight M I B
K '80 parts by weight MEK
95 parts by weight of these magnetic paints were applied onto a 12 μs thick polyester film, dried, and calendered to form a magnetic layer to obtain a magnetic tape sample.The coating thickness after calendering was 0.8. It was a door. Some samples were dried in a magnetic field of 6000 Oe perpendicular to the coating surface to vertically align the ultrafine particle samples. Table 2 shows the presence or absence of this orientation treatment in a magnetic field.

Table 2 shows the coercive force in the in-plane direction of the magnetic layer and the squareness ratio in the in-plane direction and in the perpendicular direction of the obtained magnetic tape sample.

Further, FIG. 2 shows a graph showing the temperature dependence of the coercive force of each tape sample.

Table 2 No.

Sanbuno Open 01 25℃ 150℃ Direction (vertical direction) 1 1 2010500.510.83 Yes 2 2 25
20400.500.65 No 3 3 2950400.
580.66 No 4 4 34603 (10,580,5
6 No 5 5 3980300.570.77 Yes From Table 2 and Figure 2, it is possible to set the coercive force to any value of 2000 Oe or less in the temperature range of room temperature or higher and 150'C or lower, and It can be seen that it is possible to orient ultrafine particles and improve the squareness ratio by orientation treatment in a magnetic field.

Therefore, it is clear that each of the above-mentioned magnetic layers can be applied to the above-mentioned second magnetic layer, and the effects of the present invention are also obvious from this.

[Preparation of magnetic tape sample■] The following magnetic tape was produced.

ii ヱ 1 included magnetic material, length 013-2 width 0, o2. A magnetic coating material was produced using acicular cobalt-containing γ-Fexe3 particles of 1.0 m and the other compositions were the same as above.

This magnetic paint was applied onto a 12 μm thick polyester film, dried while being oriented in a magnetic field in the longitudinal direction of the film, and further calendered to obtain a magnetic tape. The thickness of the magnetic layer was 3.5-.

The coercive force of magnetic tape A was measured using a vibrating sample magnetometer and was found to be 850 Oe.

Magnetic tape B was obtained in the same manner as magnetic tape A, except that needle-shaped metallic iron particles with a length of 0.15 mm and a width of 0.02 mm were used as the magnetic material. The thickness of the magnetic layer was 2.5 pm, and the coercive force was 1560 Oe. A magnetic paint was applied, dried and calendered to form a second magnetic layer having a thickness of 0.5 μm.

LL: The magnetic paint used for magnetic tape samples No. 5 shown in Table 2 above was applied onto the magnetic layer of Niotan magnetic tape B, and dried while performing orientation treatment in a vertical magnetic field. Next, a second magnetic layer having a thickness of 0.4 μm was formed by calendering.

14 to 1 The magnetic paint used in the production of magnetic tape B is applied onto the magnetic layer of magnetic tape A, dried while being oriented in a magnetic field in the longitudinal direction of the film, and then calendered to form a A second magnetic layer having a thickness of .8 μm was formed.

Each magnetic tape obtained as described above was cut into 1/2 inch width pieces with a gap length of 0. Recording and reproducing characteristics were measured using a 2 μm amorphous magnetic head at a relative speed of 5 to 8 m/s.

The measurement results of reproduction output in long wavelength recording and short wavelength recording are shown in Tables 3 and 4 below.

Table 3 shows that short wavelength recording was performed by recording a 7.25 MHz sine wave signal, and long wavelength recording was performed by recording a 387 k) Iz sine wave signal.
Of these, magnetic tapes A, B, and E were all recorded at room temperature, and magnetic tapes C and D were recorded only at a short wavelength of 7.25 M)lz by adjusting the temperature of the recording portion to 90°C. In addition,
Long wavelength recording was performed after short wavelength recording.

In Table 4, a signal obtained by superimposing a 7.25 MHz signal and a 387 kHz signal was recorded, and the output of each frequency component was measured. Of these, recording was performed on magnetic tape B at room temperature, and on magnetic tape C, the temperature of the recording area was adjusted to 90°C.

Table 3 Magnetic playback output (dB) Tape 387kHz 7.25MHz
(Wavelength 15μ) (Wavelength o, g, m) A (comparison) B (comparison) (comparison) + 6 + 3 - 〇.

+ 1 5 +2 +5 Table 4 Tape 387kllz 7.25. M
Hz (wavelength 15 μm) (wavelength 0.8 μm) B (comparison) 00 C+3, +3 As shown in Tables 3 and 4, magnetic tapes C and D to which the present invention is applied have extremely good short wavelength recording characteristics. It also has excellent long wavelength recording characteristics.

In addition, from the above results, short wavelength recording was performed under heating,
It can be seen that if long wavelength recording is performed at room temperature, short wavelength recording and long wavelength recording can be performed separately.

Therefore, according to the present invention, it is possible to perform short wavelength recording and long wavelength recording using different magnetic heads, and it is also possible to use magnetic heads with optimal gap lengths for each.

The effects of the present invention are clear from the above examples.

<Effects of the Invention> According to the present invention, short wavelength characteristics can be improved in magnetic recording with a wide recording wavelength range, and the security of recorded information is high.

[Brief explanation of drawings]

FIG. 1a is an explanatory diagram of a preferred embodiment of the thermomagnetic recording method of the present invention. FIG. 1b is a graph showing the temperature distribution of the second magnetic layer in FIG. 1a. FIG. 1c is a graph showing the coercive force distribution of the second magnetic layer in FIG. 1a. FIG. 2 is a graph showing the relationship between temperature and coercive force of a magnetic layer containing ultrafine ferromagnetic particles. Figure 3 shows a DC
FIG. 1 is a schematic cross-sectional view of a reactor using plasma. FIG. 4 shows an IC which is a preferred example of a ferromagnetic ultrafine particle manufacturing device.
1 is a schematic cross-sectional view of a reactor using P. Explanation of symbols l...Reactor 10...Ultrafine particles 2...Evaporation section 2I...Plasma jet generation means 211...Plasma jet 22...Raw material powder supply means 23...Heat-resistant material 24...Insulating material 3...Cooling part 31...Cooling gas supply port 4...Collecting part 100...Thermomagnetism/recording medium 110...Nonmagnetic substrate 111...First magnetic Layer 12...Second magnetic layer 20...Heating means 30...Magnetic head

Claims (8)

[Claims] (1) A method for performing magnetic recording on a magnetic recording medium having a first magnetic layer and a second magnetic layer sequentially on a non-magnetic substrate, the coercive force of the second magnetic layer at room temperature being the same as that of the first magnetic layer at room temperature. higher than the coercive force, and the Curie point of the second magnetic layer is 20
0°C or lower, the second magnetic layer is heated to reduce its coercive force, and the second magnetic layer with the reduced coercive force mainly records short wavelength components, and the first magnetic layer mainly records long wavelength components. A thermomagnetic recording method characterized by recording. (2) The thermomagnetic recording method according to claim 1, wherein the coercive force of the second magnetic layer is greater than or equal to the coercive force of the first magnetic layer during recording. (3) Claim 1, wherein the short wavelength component is recorded in the heated second magnetic layer, and the long wavelength component is recorded in the first magnetic layer at room temperature.
The thermomagnetic recording method described in . (4) A thermomagnetic recording medium having a first magnetic layer and a second magnetic layer sequentially on a substrate, wherein the coercive force of the second magnetic layer at room temperature is higher than the coercive force of the first magnetic layer at room temperature; The Curie point of the magnetic layer is 20
1. A thermomagnetic recording medium characterized in that the temperature is 0° C. or lower, short wavelength components are mainly recorded in a second magnetic layer, and long wavelength components are mainly recorded in a first magnetic layer. (5) The coercive force of the second magnetic layer is 2000O at room temperature.
5. The thermomagnetic recording medium according to claim 4, wherein the thermomagnetic recording medium is higher than e and 200 Oe or less at 150°C. (6) The thermomagnetic recording medium according to claim 4 or 5, wherein the thickness of the second magnetic layer is less than or equal to the thickness of the first magnetic layer. (7) The second magnetic layer contains ferromagnetic ultrafine particles containing a Fe_2P type hexagonal crystal structure mainly composed of Fe, Co and P and a binder. Thermomagnetic recording medium. (8) The thermomagnetic recording medium according to any one of claims 4 to 7, wherein the second magnetic layer is magnetically perpendicularly oriented.