JPH03280214A - Perpendicular magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To produce a magnetic recording medium having excellent perpendicular magnetic characteristics with good mass productivity by forming a FeCo-N magnetic thin film on a nonmagnetic substrate in a manner that this magnetic thin film has perpendicular magnetic anisotropy and a column-like structure in which the crystalline structure grows in the perpendicular direction to the substrate surface. CONSTITUTION:The perpendicular magnetic recording medium having an iron nitride magnetic layer having excellent perpendicular magnetic anisotropy is obtained by forming a FeCo-N magnetic thin film on a nonmagnetic substrate. This magnetic thin film consists of a partially nitrized alloy having the atomic compsn. ratio of Fe and Co expressed by Fe100-xCox (0<x<50), and has perpendicular magnetic anisotropy and a column-like structure in which crystalline structure grows in the perpendicular direction to the substrate surface. In the production process, the nonmagnetic substrate 7 is heated in a vacuum chamber 1, to which vapors of iron and cobalt are deposited from the perpendicular direction to the substrate surface. At the same time, nitrogen plasma 12 containing nytrogen ions and electrons is made to irradiate the vapor-deposited area. Thus, the FeCo-N magnetic thin film is formed on the substrate 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a perpendicular magnetic recording medium whose magnetic layer is a ferromagnetic metal thin film made of iron-cobalt nitride, and a method for manufacturing the same.

(b) Prior art The perpendicular magnetic recording announced by Kotoki et al. of Tohoku University is a recording method that is essentially suitable for high-density recording because the self-demagnetizing effect is suppressed as the recording density increases. As media for perpendicular magnetic recording, Co--Cr films made by sputtering or vacuum evaporation have been announced.

Although a Co--Cr film has large magnetic anisotropy and saturation magnetization and is excellent as a perpendicular recording medium, Co has a problem because it is expensive. For example, Japanese Patent Application Laid-Open No. 59-228705 (HOI F 1
0/18), an inexpensive FeN-based perpendicular magnetic recording medium based on Fe has been proposed.

This is a medium mainly composed of hexagonal iron nitride (ε-Few~, N), and contains iron, 7'-Fe4N, t -Fe,
-, N, ζ-Fe, and at least one powder selected from Fe or its nitrides such as N, a powder sintered body, or a bulk in an Ar gas flow or a mixed gas flow of Ar and nitrogen, Alternatively, it is formed by physical vapor deposition (sputtering method, vacuum evaporation method) in a mixed gas flow of Ar, nitrogen, and hydrogen.

However, with the above-mentioned thin film magnetic material mainly composed of orthogonal iron nitride, a magnetic layer cannot be formed at high speed, and the magnetic recording medium is not suitable for mass production.

Further, as a magnetic medium having perpendicular magnetic anisotropy that can be formed at high speed, an FeN-based perpendicular magnetic recording medium as shown in Japanese Patent Application No. 1-208130 has been proposed. It has a compositional structure consisting mainly of paramagnetic iron nitride (ζ-Fe, N) and ferromagnetic iron nitride (α-Fe and γ'-Fe4N phases) that is responsible for magnetization. FeN has a fine columnar structure and exhibits perpendicular magnetic anisotropy
This is a medium that has a thin film based on the magnetic layer as its magnetic layer. Such a medium involves depositing iron vapor onto a moderately heated nonmagnetic substrate from a direction perpendicular to the top surface of the substrate, and simultaneously irradiating the vapor deposition area with nitrogen plasma containing nitrogen ions and electrons. formed at high speed.

However, such iron nitride-based magnetic recording media are
Compared to the o-Cr film, the perpendicular magnetic anisotropy field (Hk), perpendicular coercive force (on Hc), and saturation magnetization (Ms) were all low, and these perpendicular magnetic properties were not sufficient.

(c) Problems to be Solved by the Invention The present invention has been made in view of the drawbacks of the above-mentioned conventional examples.
The object of the present invention is to provide a perpendicular magnetic recording medium having an iron nitride magnetic layer having excellent perpendicular magnetic anisotropy and a method for manufacturing the same.

(d) Means for Solving the Problems The perpendicular magnetic recording medium of the present invention is provided on a nonmagnetic substrate with an atomic weight composition ratio of iron and cobalt of F e . -xCo! (0
<X<50) consisting of a partial nitride of an alloy,
The present invention is characterized in that a FeCo--N magnetic thin film having perpendicular magnetic anisotropy and having a columnar crystal structure extending in a direction perpendicular to the upper surface of the substrate is deposited.

Further, in the method for manufacturing a perpendicular magnetic recording medium of the present invention, iron/cobalt vapor is deposited onto a heated nonmagnetic substrate from a direction perpendicular to the upper surface of the substrate, and at the same time, nitrogen ions and electrons are applied to the vapor deposition portion. The present invention is characterized in that a FeCo--N based magnetic thin film is deposited and formed on the substrate by irradiating nitrogen containing plasma.

(E) Effect In the perpendicular magnetic recording medium having the above structure, the paramagnetic (room temperature) iron nitride phase (c −Fe *−*N Ll<xis, ?+,
With the crystallization of ζ-Fe, N), the ferromagnetic phase (α-F
A magnetic separation effect occurs in the phase separation with e, 7'-Fe, N, a-Co, etc.), and this synergizes with the shape anisotropy due to the fine columnar structure extending perpendicularly to the top surface of the substrate. An iron-cobalt partial nitride magnetic layer having excellent perpendicular magnetic anisotropy is formed.

Further, in the above-described manufacturing method, crystallization of FeCo-H progresses due to the interaction between ion irradiation in a low kinetic energy region from the plasma generation chamber and an appropriate substrate temperature.

(F) Embodiment FIG. 1 is a schematic cross-sectional view of an apparatus for manufacturing a perpendicular magnetic recording medium by the ion-assisted vapor deposition method used in this embodiment.

In the figure (1), the inside is lXl0-'T due to the exhaust system (2).
This is a vacuum chamber maintained at a high vacuum of less than orr, and a crucible (3), a substrate holder (4), and a plasma generation Toyama are arranged inside the vacuum chamber (1). The crucible (3
An iron-cobalt alloy (6), which is an evaporation source, is housed in the chamber. A non-magnetic substrate (7) is mounted on the lower surface of the substrate holder (4), and the crucible (3) is placed directly below the substrate (7). Further, a heater (not shown) is installed inside the substrate holder (4), and the temperature of the substrate (7) is controlled by the heater. The plasma generation chamber has a filament (
8) and an anode (9) are attached, and a solenoid coil (10) is wound around the circumferential surface. The filament (8) is supplied with a voltage of 20 to 30
A current is flowing, and a positive voltage of 100 V is applied to the anode (9) by the DC power supply (Ilb). Furthermore, an electrically grounded porous grid (13) is attached to the opening on the plasma (12) emission side of the plasma generation chamber l, and the grid (13) allows the roof of the plasma generation chamber to be closed. A pressure difference occurs between the inside and outside. (1
5) is a gas introduction pipe for introducing nitrogen gas into the plasma generation chamber.

In the manufacturing apparatus of this embodiment described above, the neutral nitrogen molecules introduced into the plasma generation chamber through the gas introduction pipe (15) are heated by the heat released from the filament (8) and accelerated by the anode (9). It is ionized by collision with electrons. The low-energy nitrogen ions and electrons generated by this ionization become nitrogen plasma (12), which is externalized from the opening of the plasma generator by the magnetic field gradient formed by the solenoid coil (10) and the pressure difference by the grid (13). is emitted radially. This emitted nitrogen plasma (12) is irradiated onto the substrate (7) at the same time as the iron-cobalt vapor (14) from the crucible (3).

Therefore, the positive charges of the nitrogen ions that have reached the substrate (7) are neutralized by electrons, and the substrate (7) is not charged up. Furthermore, since the kinetic energy of the nitrogen ions and electrons is as small as 100 eV or less, the iron nitride cobalt partial nitride magnetic thin film (hereinafter referred to as FeCo-N magnetic thin film) formed on the substrate (7) does not undergo thermal dissociation.

A FeCo-N magnetic thin film was formed on a film substrate using the above-mentioned manufacturing apparatus under the following conditions.

-Film forming conditions- Back pressure nitrogen gas pressure Film formation speed Nitrogen ion current density Kinetic energy of nitrogen ions Angle of incidence of iron-cobalt vapor Film substrate temperature FeCo composition ratio (Alloy composition ratio of evaporation source) IXIO-’Torr or less 2X10-’Torr 100-750 people/m1n 2.0mA/cm 100eV or less 90° 100℃ Fe+*o+Fe5aCO+o+ FevoCOsoJeaoCOao+ Fe5oCO*oJesoCOto+ Co. .

Figures 2(a) and 2(b) show Fe film formed under the above-mentioned film formation conditions.
Co content and perpendicular magnetic properties in FeCo of Co-N magnetic thin film (perpendicular magnetic anisotropy field H, k, perpendicular coercive force Hc
It shows the relationship between soil and saturation magnetization (4πM s ). The Co content is FeCo- formed under each condition.
It was obtained by measuring an N magnetic thin film by XPS analysis (electron spectroscopy). In addition, Fig. 2(a) shows the saturation magnetization 4πM
Figure 2(b) shows the data for a sample in which s is 3.2 to 3.6K Gauss, and the nitrogen content is 1lat%.
This is data for a sample.

As can be seen from Figure 2(a), the perpendicular magnetic anisotropy field Hk of the FeCo-N magnetic thin film is 2.8KO of the FeCo-N magnetic thin film.
Fe ttco * where the atomic weight composition ratio of Fe and Co is 77:23, which increases from e to Co content.
The maximum value is about 4.0 KOe when the s-N magnetic thin film is used, and it decreases as the Co content increases, and the CO content reaches 60 KOe.
When the at% is increased, it becomes smaller than that of a FeN magnetic thin film. This result is expressed as perpendicular magnetic anisotropy field Hk and anisotropy energy Ku.
Applying the relational expression Hk = 2 K u / M s, it can be seen that the perpendicular magnetic anisotropy field Hk improves as the anisotropy energy Ku of the magnetic thin film increases with the addition of Co (within the range of 0 to 32 at%). I see what you did. Furthermore, Co
The perpendicular magnetic anisotropy field Hk of the N magnetic thin film is 2.3 KOe, which is a lower value than that of the FeN magnetic thin film.

In addition, the perpendicular coercive force of FeCo-N magnetic thin film Hc soil Co
The content dependence shows almost the same tendency as the perpendicular magnetic anisotropy field Hk, and the maximum value is 60% when the Co content is around 23at%.
00e, and at a Co content of 80 at% or less, Fe
It shows a higher value than the N magnetic thin film.

The magnetic properties of CoCr perpendicular magnetic tape are Hk2.2kO
It has been announced that the
, Na3.1988JP, 63Table 2) As the magnetic properties of the perpendicularly magnetized film, the perpendicular magnetic anisotropy field Hk may be of this magnitude from the standpoint of electromagnetic conversion characteristics, and the saturation magnetization 4πMS is designed to be relatively high. There is. This shows that it is important to compare the magnitude of the saturation magnetization 4πMs in magnetic thin films having similar perpendicular magnetic anisotropy fields Hk.

Furthermore, as can be seen from Fig. 2(b), the saturation magnetization 4πMs of the FeCo-N magnetic thin film shows a maximum value of 3.4 kGauss when the CO content is around 25 at%, and when the CO content is less than 50 at%, the FeCo-N magnetic thin film has a maximum value of 3.4 kGauss. This value is higher than that of magnetic thin films.

From the above, when the Co content is 50 at% or less,
That is, the atomic weight composition ratio of iron and cobalt is Ferae-xc.
The FeCo-N magnetic thin film represented by Ox (0<X<50) is exposed to a perpendicular magnetic anisotropy field H with respect to the FeN magnetic thin film.
It can be seen that k, vertical coercive force Hc, and saturation magnetization 4πMs all improve.

3, 4, 5, 6, 7, 8, and 9 show various FeCo films formed under the above-mentioned film formation conditions, respectively.
The saturation magnetization dependence of the perpendicular magnetic properties of a -N magnetic thin film is shown.

For the perpendicular magnetic properties of the FeN magnetic thin film shown in Fig. 3, the atomic weight composition ratio of Fe and Co shown in Fig. 4 is 94:6.
The Fe□Co5-N magnetic thin film has a saturation magnetization of 4πMs
In the range of 2000-5000 Gauss, the vertical coercive force Hc hardly changes, but the perpendicular magnetic anisotropy field H
k will improve. Further, the atomic weight composition ratio of Fe and Co shown in FIGS. 5, 6, and 7, respectively, is 76:24.
．． 77:23.66: FeraCOx which is 34
N magnetic thin film, Fettcoxs-N magnetic thin film, Fem5COs*-N magnetic thin film have a saturation magnetization of 4 yr.
When M s is in the range of 2000 to 5000 Gauss, both the perpendicular magnetic anisotropy field Hk and the perpendicular coercivity and magnetic force Hc are improved for the FeN magnetic thin film. Furthermore, the Fe 4gCo 1s-N magnetic thin film shown in FIG. 8 and the Co-N magnetic thin film shown in FIG. The perpendicular magnetic anisotropy field Hk is significantly reduced. From the above, the saturation magnetization 4πMs is 2000 to 5000 Gaus
Within the range of s, the atomic weight composition ratio of Fe and Co is 94
:6 to 66:34, the perpendicular magnetic anisotropy field Hk of the FeCo-N magnetic thin film is improved compared to the FeN magnetic thin film, and in particular, the atomic weight composition ratio of Fe and Co is 77:3.
23-66: The FeCo-N magnetic thin film within the range of 34 has a perpendicular magnetic anisotropy field Hk with respect to the FeN magnetic thin film.
It can be seen that both the vertical coercive force Hc and the perpendicular coercive force Hc are improved.

Figures 10(a), (b), and (c) show the microstructures of an FeN magnetic thin film, a Fe5sColtN magnetic thin film with an atomic weight composition ratio of Fe and Co of 68:32, and a CoN magnetic thin film, respectively, using a scanning electron microscope. This is a cross-sectional photograph.

As can be seen from Figure 10(a) and (b), in the FeN magnetic thin film and FeaaCojz-N magnetic thin film with good perpendicular anisotropy magnetic field, the fine columnar structure is perpendicular to the substrate from the substrate interface to the film surface. observed to grow in the direction. However, there is no significant difference in the particle size of the columnar particles between the two, and both are about 500 particles. In addition, as can be seen from Figure 10(C), Co has an inferior perpendicular anisotropy field.
In the N magnetic thin film, the fine columnar structure is unclear and it is observed that it has a columnless structure. In other words, from the above results, it is clear that in order for a magnetic thin film to have good perpendicular magnetic anisotropy, it is essential to form a fine columnar structure with a clear cross-sectional shape. As with FeN magnetic thin films, shape magnetic anisotropy is considered to be the main origin of the magnetic properties.

Table 1 shows the magnetic properties of the magnetic thin films shown in FIGS. 10(a), 10(b), and 10(c), respectively.

FIG. 11 of Table 1 shows the change in the X-ray diffraction pattern of the FeCo-N magnetic thin film when the degree of nitridation of the FeCo-N magnetic thin film is changed by changing the deposition rate. FeCo
The degree of nitridation of the −N magnetic thin film increases as the film formation rate decreases. Samples A and B shown in FIGS. 11(a), (b), and (c), respectively.
, C film formation rate is 360 people/min, 328 people/min.
min, 100 people/min.

Table 2 shows the F of samples A, B, and C used for the analysis in Figure 11.
This is a summary of the production conditions, magnetic properties, and generated phases identified from the peak diffraction angle of the eCo-N magnetic thin film.

As can be seen from the margins in Figure 11 and Table 2 below, each sample A, B, and C are
, ε Few-sN, ζ-FesN, a-Co, γ-C
o, N, δ-CO! A mixed pattern of N is shown. FeCo-N with high anisotropic magnetic field like samples A and H
Looking at the perpendicularly magnetized film, it can be seen that unnitrided metal phases (α-Fe, α-Co) remain in the film, and the film is in a partially nitrided state. That is, sample A,
It can be seen that the FeCo--N magnetic thin film of B is made of iron-cobalt partial nitride. The FeCo--N magnetic thin film is composed of an aggregate of these phases, and the composition ratio largely depends on the degree of nitridation of the film. That is, when the degree of nitridation is increased, metal phases (a-Fe, a-Co) and 7''-Fe are formed.

The N phase, etc. decreases, and the highly nitrided phase (Fe, N, ε-Fe
, −, N, ζ-F e , N, 7-Co , N, δ-
Co, N) increases. t F e x N (s<
x<! , +t)1ζ-FexN phase exhibits paramagnetic properties at room temperature, so the reason why the saturation magnetization decreased as the film forming rate decreased is considered to be that the composition ratio of these paramagnetic phases increased. The FeCo-N magnetic thin film contains a ferromagnetic component (α-F
e, r”-Fe+N, Fe, N, ε-FeXN,,
47<x<3. , a-Co, 7Co5N) and the paramagnetic component (t-Fe x N (!<x<y, 471%
ζ-Fe.

N, δ-Co, N) coexist, FeCo-N
One of the origins of the perpendicular magnetic anisotropy in a magnetic thin film is considered to be the magnetic separation effect of the ferromagnetic phase by the paramagnetic phase, similar to the FeN magnetic thin film.

Figures 12(a) and (b) show F containing 32 at% CO.
e ssCo st-N magnetic thin film magnetic properties Hk3.3
KOe, Hc soil 52000e, 4πMs3.4KGau
It is a figure showing the XPS spectrum of ss.

If we pay attention to the 2P3/2 level of Fe shown in Figure 12(a), there is a Fe peak at 707 eV, which is superimposed on the nitridation with a broad chemical shift to the high energy side due to chemical bonding with nitrogen. Iron peaks can be seen. Also, the first
Focusing on the 2P3/2 level of Co shown in Figure 2(b), the proportion of peaks chemically shifted by nitridation is smaller than that of Fe, indicating that most of the CO exists in a metallic state. I understand. From the above results, it is clear that Co is less likely to be nitrided than Fe, and this means that by adding CO, which has a different affinity for nitriding, the state of nitride formation during the film growth process can be changed. This shows that it is possible to expect an improvement in the magnetic separation effect of the ferromagnetic phase by the paramagnetic nitride phase, that is, an improvement in the magnetic anisotropy energy (Ku).

Table 3 shows the magnetic properties and compositional analysis results of the FeCo--N magnetic thin film used in the XPS analysis.

Table 3 Comparing the magnetic properties of E with the same nitridation content, that is, the same degree of nitridation, shows that C in the magnetic thin film is
It is clear that the higher the o content, the better the saturation magnetization. The improvement in the saturation magnetization of the FeCo-N magnetic thin film by adding CO is due to the fact that the magnetic moment of the ferromagnetic a-Fe phase, which is responsible for magnetization, is C.

This is explained by the fact that it changes with the amount added.

Tables 4 and 5 show FeCo films formed under the above film formation conditions.
-The magnetic properties of the N magnetic thin film and the FeN magnetic thin film are shown.

(Note) FeCollt is the composition of the first sauce in Table 4. (Note) FeCo1ml! I of I! Table 5 As can be seen from Tables 4 and 5, by adding an appropriate amount of Co to the FeN magnetic thin film, the magnetic thin film has a perpendicular magnetic anisotropy field of Hk, a perpendicular coercive force of HC, and a saturation magnetization of 4πM.
An improvement in s was observed. The reason for the improvement in the perpendicular magnetic anisotropy field Hk is that the addition of Co, which has a different affinity for nitriding, changes the manner in which nitrides are formed during the film growth process, which increases the ferromagnetic property due to the paramagnetic nitride phase. One point is that the phase separation of the phases is promoted and the magnetic separation effect is improved.

Further, the reason for the improvement in the perpendicular coercive force Hc is due to the above-mentioned improvement in the perpendicular magnetic anisotropy field Hk. Further, the reason for the improvement in the saturation magnetization 4πMs is considered to be that the addition of Co increased the magnetic moment of the ferromagnetic α-Fe phase responsible for magnetization.

Furthermore, according to the method for forming the magnetic Wi film described above, the film formation rate is twice as high (100 to 750 people/m1n) as compared to when using the sputtering method (approximately 50 people/m1n). It is clear that the thin film formation method is suitable for mass production.

(G) Effects of the Invention According to the present invention, a perpendicular magnetic recording medium with excellent perpendicular magnetic properties can be provided.

Further, according to the present invention, it is possible to provide a method for manufacturing a perpendicular magnetic recording medium, which allows the above-mentioned magnetic recording medium having excellent perpendicular magnetic properties to be manufactured with good mass productivity.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the manufacturing apparatus of the present invention, and FIG.
C of perpendicular magnetic properties of Co--N magnetic thin film. Diagrams showing content dependence, Figures 3, 4, 5, and 6
7, 8 and 9 are diagrams showing the saturation magnetization dependence of the perpendicular magnetic properties of the FeCo-N magnetic thin film, respectively.
Figure 0 is a scanning electron micrograph showing the crystal structure of the magnetic thin film, Figure 11 is the X-ray diffraction pattern of the FeCo-N magnetic thin film, and Figure 12 is the xps spectrum of the FeCo-N magnetic thin film. be.

Claims (2)

[Claims] (1) A partial nitride of an alloy with an atomic weight composition ratio of iron and cobalt expressed as Fe_1_0_0_-_xCo_X (0<X<50) is formed on a nonmagnetic substrate, and the crystal structure is vertical to the top surface of the substrate. A perpendicular magnetic recording medium characterized in that a FeCo-N based magnetic thin film having an elongated columnar structure and having perpendicular magnetic anisotropy is deposited. (2) By depositing iron/cobalt vapor onto a heated nonmagnetic substrate from a direction perpendicular to the upper surface of the substrate, and at the same time irradiating the vapor deposition area with nitrogen plasma containing nitrogen ions and electrons, the substrate is heated. 1. A method of manufacturing a perpendicular magnetic recording medium, which comprises depositing an FeCo--N magnetic thin film thereon.