JPH1166532A - Perpendicular magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a medium noise when a signal is reproduced by an MR head and to obtain a high S/N ratio by a method wherein the saturation magnetization of a vertical recording layer in a perpendicular magnetic recording medium having a three-layer structure in which a hard magnetic substrate layer, a soft magnetic substrate layer and the vertical recording layer are laminated on a nonmagnetic substrate is set at less than a specific value and the film thickness of the vertical recording layer is set at a specific thickness or higher. SOLUTION: A film by CoSm17 (in atomic %; in the following the same is applied) in thickness of 150 nm is formed, by a magnetron sputtering method, on a mirror-finished disk- shaped soda lime glass substrate, and a hard magnetic substrate layer is formed. In the same manner, a CoZr1 to 6 Nb3 film in thickness of 500 nm is formed on it as a soft magnetic substrate layer, and a CoCrTa film is formed as a vertical recording layer by controlling the arrangement number of Cr chips. An Ar gas pressure in the formation of the film is set at 0.5 mTorr, a substrate temperature is set at about 250 deg.C, the saturation magnetization of the vertical recording layer in a three-layer structure is set at less than 520 emu/cc, and the film thickness of the vertical recording layer is set at 40 nm or higher. Thereby, even when an MR head is used, it is possible to obtain a perpendicular magnetic recording medium in which a medium noise is reduced, in which an output is high, in which an S/N ratio is high and in which an excellent high-density characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a perpendicular magnetic recording medium having a three-layer structure.

[0002]

2. Description of the Related Art The perpendicular recording method has attracted attention because it can perform high-density recording as compared with the currently used in-plane recording method.
A two-layer structure in which a soft magnetic underlayer and a perpendicular recording layer are stacked has been widely studied. The perpendicular magnetic recording medium having this two-layer structure can perform efficient recording / reproduction by combining with a single pole type head. Above all, C
It is known that a two-layer film medium using an o-Zr-based amorphous soft magnetic film as a base layer can realize a perpendicular recording layer having a sharp perpendicular orientation, and is particularly effective for improving recording efficiency. (JP-A-3-278595).

However, in the above-described perpendicular magnetic recording medium, particularly in a disk-shaped medium, there is a problem that the signal intensity is attenuated with time only by rotating the medium after recording the signal. . This phenomenon occurs because a magnetic field generated from a domain wall of the soft magnetic underlayer erases a recording signal of the perpendicular recording layer. In addition to it,
The magnetic field generated from the domain wall of the soft magnetic underlayer also has a problem that the medium noise also increases. Therefore, the present inventors have found that a three-layer structure in which an in-plane oriented hard magnetic layer having magnetization in the radial direction is provided between a nonmagnetic substrate and a soft magnetic underlayer, impairing the recording / reproducing characteristics. Instead, a device in which demagnetization caused by rotation of the medium as described above is prevented and medium noise is reduced has been previously proposed (Japanese Patent Laid-Open No. 7-129946).

[0004]

On the other hand, in recent years, with the advent of a magnetoresistive (MR) head, the reproduction characteristics of magnetic recording have been dramatically improved, and attempts have been made to use the MR head also in the perpendicular recording system. It has been done. However, since the MR head has extremely high sensitivity, a large reproduction output can be obtained, but the medium noise is also detected largely. Even when the MR head is used for the above-described three-layered perpendicular recording medium, the medium noise is high. It is a problem.

[0005]

Means for Solving the Problems The present inventors have conducted various studies on a perpendicular magnetic recording medium having a three-layer structure in order to reduce medium noise and achieve a high S / N, particularly when reproduced by an MR head. As a result, the optimum ranges of the saturation magnetization and the thickness of the perpendicular recording layer were found. That is, according to the present invention, the saturation magnetization of the perpendicular recording layer of the perpendicular magnetic recording medium having the three-layer structure in which the hard magnetic underlayer, the soft magnetic underlayer, and the perpendicular recording layer are laminated on the nonmagnetic substrate is 520 emu / cc. Less, the film thickness is 40n
m or more are provided.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A perpendicular magnetic recording medium according to the present invention has a three-layer structure in which a hard magnetic pinning layer, a soft magnetic underlayer, and a perpendicular recording layer are laminated in this order on a nonmagnetic substrate. A protective layer may be further formed on the perpendicular recording layer. First, the hard magnetic pinning layer has a function of fixing the magnetic domain of the soft magnetic underlayer formed thereon. For example, CoSm, CoCrTa, Co, CoP
It is formed of t, CoCrPt, CoCrTaPt, or the like, and its film thickness may be in a range where the soft magnetic underlayer can be sufficiently pinned, and is, for example, about 10 nm or more. The soft magnetic underlayer is formed of, for example, a Co-Zr-based amorphous alloy such as CoZrNb or CoZrTa, and the thickness thereof is preferably in a range that can realize sufficient recording / reproducing characteristics and can be pinned by the pinning layer. For example, it is about 200 nm to 2 μm.

Further, the perpendicular recording layer is made of, for example, Co-P
Alloy, Co-Ni-P alloy, Co-γ-Fe ₂ O ₃ alloy, or CoCrTa, CoCrPt, CoC
made of Co-Cr-based alloy such as RTaPt, its saturation magnetization (hereinafter referred to as M _s) less than 520emu / cc, and the film thickness thereof is required to be 40nm or more. When M _s is 520 emu / cc or more,
Satisfactory S / N cannot be obtained. The preferred range of M _s is a 280~450emu / cc. on the other hand,
When the thickness of the perpendicular recording layer is less than 40 nm, H _c
⊥ decreases. The preferred thickness of the perpendicular recording layer is 4
0-100 nm.

Various means can be considered for setting the perpendicular recording layer to a desired M _s value.
When using CrTa, by controlling the content of Cr, specifically, by the content of Cr is adjusted alloy composition to exceed 16 atomic%, it is possible to obtain a desired M _s value . Further, the M of the above-described perpendicular recording layer
_It is preferable that _{s and the} film thickness are appropriately selected from the above ranges according to the required characteristics of the finally obtained perpendicular recording medium. The perpendicular magnetic recording medium having such a configuration can be manufactured by forming each layer on a non-magnetic substrate by, for example, magnetron sputtering.

<Example> The present invention will be specifically described with reference to the following examples. (1) Manufacture of perpendicular magnetic recording medium On a mirror-finished disk-shaped soda lime glass substrate, first, CoSm ₁₇ (the numerical value is at%, the same applies hereinafter) is formed into a 150 nm film by magnetron sputtering to form a hard magnetic underlayer. Was formed. Thereon similarly by the magnetron sputtering method, as the soft magnetic underlayer, a CoZr ₄ ~ ₆ Nb ₃ ~ ₅ film 500 nm, as subsequently immediately perpendicular recording layer, Co
CrTa was deposited. The composition of the CoCrTa vertical layer was controlled by the number of Cr chips arranged on the CoCr _11.5 Ta ₄ target.

The Ar gas pressure during film formation is 0.5 mTo
rr, the substrate temperature is room temperature during the formation of _{CoSm 17, CoZr 4 ~ 6 Nb} 3 ~ 5, the time of deposition of CoCrTa was about 250 ° C.. During film formation, the magnetron magnet
A magnetic field of about 4 kA / m is applied in the radial direction of the substrate, and the magnetization and the axis of easy magnetization of the hard magnetic underlayer and the soft magnetic underlayer are aligned in the radial direction. Further, a SiO ₂ film having a thickness of 5 nm was formed as a protective film on the surface layer. With respect to the perpendicular magnetic recording medium thus obtained, the following characteristics were evaluated. In each of the evaluation tests, only an inductive single magnetic pole (SPT) head having a track width of 7 μm, a main pole thickness of 0.3 μm, and a coil turn number of 40 was used for signal recording. Both an SPT head and a SAL bias type MR head having a track width of 2.5 μm and a shield gap of 0.4 μm were used. In addition, linear velocity v5-8 m / s, flying height 6
The measurement was performed under the condition of 0 nm.

(2) Evaluation Test (A) Composition Dependence of Magnetic Properties and Crystal Orientation of Perpendicular Recording Layer The composition dependence of magnetic properties and crystal orientation of a CoCrTa perpendicular recording layer was examined. FIG. 1 is a diagram showing the relationship between the Cr content of the CoCrTa perpendicular recording layer and the magnetic properties and crystal orientation. At this time, the content of Ta was 3 to 4 at% as a result of ICP analysis. As is apparent from the figure, H _cと な り has a maximum value of 2800 to 3000 [Oe] when Cr is 16 at%, which is close to the conventional composition, and 16 at
% Tended to gradually decrease as it decreased or increased. On the other hand, Δθ _{50 as} an index of crystal orientation is C
3 deg. regardless of the r content. Was almost constant, and it was confirmed that good crystal orientation was maintained regardless of the composition. This is because the amorphous CoZrNb underlayer (soft magnetic underlayer) promotes the perpendicularity of the CoCrTa perpendicular recording layer.

[0012] (B) in the film thickness dependency diagram 2 of a vertical layer the composition of the perpendicular recording layer when the CoCr ₂₀ Ta _3.5, showed a film thickness dependency of the perpendicular recording layer. As is clear from the figure, it was found that H _cほ ぼ almost reached saturation when the film thickness δ was 40 to 50 nm.

(C) Surface SEM observation of vertical layer FIGS. 3 (a) to 3 (c) are SEM photographs of the surface of the CoCrTa vertical recording layer having three compositions when the film thickness δ is 50 nm. In any of the compositions, crystal grains unique to CoCrTa were observed. Almost no difference in crystal grains due to the difference in composition was observed, and the particle size was approximately 40 to 50 nm, which was almost the same as the film thickness. The relationship between the magnetic properties showed the highest H _c is the case of Cr16at% shown in the diagram (a).

[0014] FIG. 4 (a) ~ (d) the composition of the perpendicular recording layer is at a CoCr ₂₀ Ta _3.5, exhibited surface SEM photograph in the case of changing the thickness [delta]. As is clear from the figure, the particle diameter increased as the film thickness δ increased. The relationship between the magnetic properties, H _c in thickness δ50nm more
⊥ was getting bigger. In general, it is known that in a CoCr-based perpendicular recording layer, composition segregation occurs in one grain. That, Cr-rich non-magnetic region is formed by segregation, Co-rich ferromagnetic region orphaned, by the single domain, it is considered that H _c ⊥ is increased. Further, as shown in FIGS. 3B and 3C, when the Cr amount is further increased, or as shown in FIGS.
It is considered that when the film thickness is 30 nm or less as in (b), the volume of the isolated Co-rich ferromagnetic region decreases, and H _c低下 decreases due to approaching superparamagnetism.

(D) Electromagnetic conversion characteristics Four types of M _s (280, 400,
520 and 700 emu / cc), a perpendicular recording medium was manufactured by changing the film thickness δ, and the following electromagnetic conversion characteristics were examined. As previously mentioned,
All signal writing is performed by the SPT head, and reading is performed by
This was performed using both the SPT head and the MR head, and the two were compared.

A) Dependence of solitary wave output E _P on M _s and film thickness The solitary wave output E _P shown in FIG. 5 generally increases as the film thickness δ and M _s increase, but M _s = 520 emu.
/ Cc and 700 emu / cc.
The cause that does not become the output is large and the M _s above 700 emu / cc, it does not increase running specific residual magnetization demagnetizing field becomes large, and, as shown in FIG. 2, H _c ⊥ is M _s = 520 emu / cc.

B) Medium noise, M of medium S / N_s, Film thickness
Dependency The medium noise Nm shown in FIG. 6 is almost the same as the output shown in FIG.
It is in a flipped relationship. Just M_s= 520 em
The reversal between u / cc and 700 emu / cc is not seen.
No, M_s= 700 emu / cc
Is getting higher. This means that the medium S / N shown in FIG.
Is well reflected in the results. That is, M_s= 700e
The S / N is the lowest at mu / cc. Also, M_s
Is 400 emu / cc or less, the highest S / N is obtained.
And a conventional perpendicular magnetic recording medium (M s = 520 emu /
cc), both SPT head and MR head
About 2 to 3 dB higher S / N was obtained. Low M_sC
oCrTa has a large Cr composition ratio and is strongly magnetic due to segregation.
Isolation of the ferromagnetic region is promoted, and the magnetic
Reduced noise due to weakened gas interaction
It is. FIG. 8 shows that the highest S / N was obtained in FIG.
Select the film thickness to be_sAnd shows the relationship between S / N
Yes, both SPT and MR heads have M_s= 400
At emu / cc, the S / N is at its maximum, and
In particular, in the MR head, M_sTo 520 emu / c
c, the conventional value of 27 dB (M_s= 52
0emu / cc)
It was confirmed that.

[0018] Ha) density of 9, showing a D ₅₀ of the high density of the index. This D
₅₀ is 100 kfc when M _s = 400 emu / cc.
i, which is the highest value. Furthermore, in order to compare the high density with the medium noise taken into account, 190 kfci
The medium S / N in the high density signal was examined. The results are shown in FIG. From this figure, M _s = 400 emu /
cc is the best, and when the film thickness is 50 nm,
A medium S / N of 15 dB or more was obtained. FIG.
4 by three-dimensional simulation when _s is changed
The medium magnetization pattern of the bit recording is shown. The magnetization in FIG. 6A is set to be 1.6 times the magnetization in FIG.
Ku of (a) is also set to be larger than Ku of (b), and H _c
Are equivalent. As a result, it was confirmed towards the smaller M _s (b) there is a lower sharp noise pattern.

In order for a high-density minute bit to exist stably, the ferromagnetic region needs to be isolated. However, when M _s = 280 emu / cc, which has the highest Cr content, the high-density characteristic is high. The reason for this is that the recording bit becomes unstable due to the approach to superparamagnetism. Further, in a magnetic recording medium having an in-plane recording layer, as the thickness of the recording layer is reduced, the effect of the demagnetizing field is reduced and the high-density characteristics are improved, but as is clear from FIGS. In the case of the perpendicular recording method, the high-density characteristics are most excellent in a region where the thickness δ of the perpendicular recording layer is somewhat large (around 50 nm).

[0020] Figure 12 is a perpendicular magnetic recording medium obtained by the present invention, the in-plane magnetic recording medium of high S / N to be used in MR heads, as well as conventional perpendicular recording layer (M _s = 520e
(mu / cc, δ = 50 nm) using the same MR head to compare the recording density characteristics. The perpendicular recording medium according to the present invention has the highest S / N,
Moreover, it was found that, as compared with the longitudinal magnetic recording medium, the higher the recording density, the greater the difference in S / N. As described above, by appropriately selecting the _Ms and the film thickness of the perpendicular recording layer in accordance with the above, it is possible to simultaneously achieve desired high output and low noise.

[0021]

As described above in detail, according to the present invention, by appropriately selecting the Ms and the film thickness of the perpendicular recording layer, the medium noise can be reduced especially when an MR head is used. It is possible to realize a perpendicular magnetic recording medium having high output, high S / N, and excellent high density characteristics.

[Brief description of the drawings]

FIG. 1 shows the Cr content of a CoCrTa perpendicular recording layer,
5 is a graph showing the relationship between M _s , H _c and crystallinity.

2 is a graph composition showed H _c and the crystallinity of the film thickness dependence of certain CoCrTa perpendicular recording layer.

FIG. 3 is an SEM photograph of a CoCrTa perpendicular recording layer surface of three types of compositions.

FIG. 4 is a SEM photograph of the surface of a CoCrTa perpendicular recording layer having a constant composition at four film thicknesses.

FIG. 5 is a graph showing the dependence of the solitary wave output on the perpendicular recording layer _Ms and the film thickness.

FIG. 6 is a graph showing the dependency of medium noise on the perpendicular recording layer _Ms and the film thickness.

FIG. 7 is a graph showing the dependency of the medium S / N on the perpendicular recording layer _Ms and the film thickness.

FIG. 8 is a graph showing the relationship between the medium S /
9 is a graph showing the dependence of N on the perpendicular recording layer _Ms and the film thickness.

[9] of D _50, is a graph showing a perpendicular recording layer M _s and film thickness dependence.

FIG. 10 is a graph showing the dependency of the perpendicular recording layer _Ms and the film thickness of the medium S / N on the high-density signal.

FIG. 11 is a diagram showing a magnetization pattern by simulation when M _s is changed.

FIG. 12 is a graph showing the dependence of the medium S / N on the composition of the perpendicular recording layer and the thickness of the medium in a high-density signal when reproduced by an MR head.

Claims (1)

[Claims] 1. A hard magnetic pinning layer on a non-magnetic substrate,
In a perpendicular magnetic recording medium having a three-layer structure in which a soft magnetic underlayer and a perpendicular recording layer are laminated, the perpendicular recording layer has a saturation magnetization of less than 520 emu / cc and a film thickness of 40 nm or more. Medium.