JPS61292220A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good reproduction output by selecting the ratio of the coercive forces which the respective layers of magnetic layers formed of upper and lower layers possess within a prescribed range. CONSTITUTION:The ratio between the coercive force in the vertical direction of the upper layer 3 of a vertical magnetic recording medium having the magnetic layers 3, 2 formed of the upper layer and lower layer and the coercive force in the intra-surface direction of the lower layer 2 is selected to the ratio expressed by the equation. The magnetic layers which the vertical magnetic recording medium has are thereby constructed as the magnetic layers having a magnetization jump so that the magnetic flux released from a magnetic head 4 advances into the lower layer 2 having low coercive force and progresses in a horizontal direction. This magnetic flux is quickly and sharply penetrated through the upper layer 3 having the high coercive force by the magnetic pole of the magnetic head and is attracted to the magnetic pole of the magnetic head and therefore the strong residual magnetization is generated and the high reproduction output is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium capable of improving perpendicular magnetic properties.

Conventional technology Generally, recording is performed on a magnetic recording medium using a magnetic head.

In order to perform reproduction, a commonly used system is to magnetize the magnetic layer of a magnetic recording medium in the longitudinal direction (in-plane direction) of the medium using a magnetic head, record the information, and then reproduce the recorded information. However, according to this method, it is known that as the recording density increases, the demagnetizing field increases, and the demagnetizing effect exerts an adverse WeW effect on high-density recording. Therefore, in recent years, a perpendicular magnetic recording method has been proposed in which the magnetic layer of a magnetic recording medium is magnetized in the perpendicular direction to eliminate the above-mentioned adverse effects. According to this, as the recording density is improved, the demagnetizing field becomes smaller, and theoretically, it is possible to perform good high-density recording without reducing residual magnetization.

Conventionally, perpendicular magnetic recording media used in this perpendicular magnetic recording system include those in which a Co--Cr film is formed on a base film by sputtering. As is well known,
The Go-Cr film has a relatively high saturation magnetization (Ms),
It is known that it is an extremely promising material as a perpendicular magnetic recording medium because it has an axis of easy magnetization perpendicular to the film surface (that is, the coercive force HC in the direction perpendicular to the film surface is large). However, as mentioned above, sputtering
- In the case of a perpendicular magnetic recording medium with a structure in which a single layer of Cr film is formed, magnetic flux cannot be concentrated at a predetermined magnetic recording position on the perpendicular magnetic recording medium (this is especially noticeable when a ring core head is used). There was a problem in that the magnetic recording medium had a sharp distribution and could not have strong perpendicular magnetization.

In order to solve the above-mentioned problem, a so-called backing layer is provided between the Co-Cr 11 and the base film, and the layer has a high magnetic permeability m<, that is, a small coercive force HC.

For example, Ni -)"e) is separately formed to have a two-layer structure, and the magnetic flux spreading in the high magnetic permeability layer is concentrated and attracted to the magnetic pole of the magnetic head at a predetermined magnetic recording position, resulting in a sharp distribution. There was also a perpendicular magnetic recording medium with a configuration capable of strong perpendicular magnetization.

Problems to be Solved by the Invention However, the above-mentioned conventional perpendicular magnetic recording medium 1, for example, Co-C
When recording on an r single-layer medium with a ring core head, the magnetic field distribution has a considerable in-plane component, so the magnetization tends to tilt during recording. In order to maintain perpendicular magnetization, perpendicular magnetic recording media have a high perpendicular anisotropy magnetic field (Hk), and the saturation magnetization (Ms) must be suppressed to a somewhat small value. Furthermore, in order to achieve a high reproduction output, it is necessary to increase the perpendicular coercive force (on Hc) and increase the thickness of the perpendicular magnetic recording medium. In addition, if the thickness dimension is increased, the so-called contact between the perpendicular magnetic recording medium and the magnetic head (sliding contact conditions at the sliding contact part of the perpendicular magnetic recording medium and the magnetic head) will deteriorate, and the perpendicular magnetic recording medium may be damaged. There was a problem in that the magnetic head was adversely affected and good perpendicular magnetic recording and reproduction could not be performed.

In addition, in the case of a two-layer perpendicular magnetic recording medium formed with a high permeability layer as an underlayer in addition to C0-CrH, Qo-Q
Since the coercive force (coercive force) 1c of the high magnetic permeability layer was extremely small (10 Qe or less) compared to the coercive force Hc (70008 or more) of rli, there was a problem in that impulsive Barkhausen noise was generated. In addition, in order to obtain a perpendicular magnetic recording medium with a two-layer structure, firstly, Fe-N, for example, is coated on a base film under predetermined conditions suitable for forming a high magnetic permeability layer.
i/Amorphous etc. is coated by sputtering, and then Co-Cr is coated under predetermined conditions suitable for forming a Co-Cr film.
Cr must be coated by sputtering, and sputtering conditions and targets must be changed each time each layer is formed, making continuous sputtering impossible.
There were problems in that the manufacturing process was complicated and mass productivity was poor.

Therefore, an object of the present invention is to provide a perpendicular magnetic recording medium that solves the above problems by selecting the ratio of coercive force of each layer of the magnetic layer formed by the upper layer and the lower layer within a predetermined range. .

Means for Solving the Problems In order to solve the above problems, the present invention provides a perpendicular magnetic recording medium having a magnetic layer formed of an upper layer and a lower layer.
The vertical coercive force of the upper layer was chosen to be 1-1c above.

Embodiment A perpendicular magnetic recording medium according to the present invention (hereinafter simply referred to as a recording medium) has a base polyimide substrate coated with at least one of cobalt (Co), chromium (Cr), niobium (Nb), and tantalum (Ta). It is obtained by sputtering using a magnetic material as a target.

Conventionally, when metal etc. (e.g. Go-Cr alloy) is sputtered onto a base, the formed III film does not form the same crystal structure in the direction perpendicular to the film surface, but rather forms an extremely thin part near the base. Various experiments (e.g., scanning electron microscopy photography) have shown that a first crystal layer with small grain size is formed first, followed by a second crystal layer with large grain size. It is becoming (
E dward R, Wuori and P
rofessor J.

H, Judy: “IIITIAL LAYEREF
FECT IN Co-CRFILMS''.

rEEE Trans, , VOL, MAG-20°N
O, 5, SEPTEMBER1984, P 774~P
775 or William G. Haines
: “VSMPROFILING OF CoC
rFIMS: A NEW ANALYTICAL
ECI-(NIQtJE”IEEE Trans,
, VOL, MAG-20, No, 5. SEPTEM
BER1984, p 812-p 814). The present inventor focused on the above viewpoint and sputtered various metals based on a Co-Cr alloy and added with a third element, thereby forming a crystal layer with a small grain size and a large grain crystal layer formed on top of the crystal layer. As a result of measuring the physical properties of the small-grain crystal layer, it was found that the coercive force of the small-grain crystal layer is much smaller than that of the large-grain crystal layer, especially when Nb or Ta is added as a third element. Understood. The present invention is characterized in that the small-grain crystal layer having a low coercive force is used as a high permeability layer, and the large-grain crystal layer having a high coercive force is used as a perpendicular magnetization layer.

Hereinafter, the results of an experiment conducted by the present inventor to measure the coercive force of a small grain crystal layer and a large grain crystal layer formed by sputtering will be described in detail. Co-0r thin film, Go-Cr
When sputtering the -Nb'flJ film and the Co-Cr-Ta thin film, the sputtering conditions were set as follows (the sputtering conditions were set equally in each case where Nb or Ta was added).

*Sputtering equipment RF magnetron sputtering equipment *Sputtering method Continuous sputtering. Preliminary exhaust pressure 1×1O-6T
After exhausting to orr, Ar gas was introduced and I
* Base polyimide (thickness 20 μm) with T Orr * Composite target with a small piece of Nb or Ta placed on a target Go-Cr alloy Made by
The composition of the thin film was measured using an energy dispersive micro analyzer (manufactured by KEVEX, hereinafter referred to as ED).
The crystal orientation was determined using an X-ray diffraction device (abbreviated as X).
(manufactured by Rigaku Denki).

Adding Nb as a third element to Go-Cr (2 to 10 at
% addition range), and FIG. 1 shows a hysteresis curve in the in-plane direction when a magnetic field of 15 KOe is applied to a recording medium sputtered to a film thickness of 0.2 μm on a polyimide base. From the same figure, the hysteresis curve suddenly rises irregularly (indicated by arrow A in the figure) in the area where the in-plane coercive force (indicated by the symbol HC/) is near zero.
, it can be seen that a so-called magnetization jump occurs. If we assume that the sputtered Co -Or -Nb Wl film always undergoes uniform crystal growth during sputtering, the magnetization jump shown in Figure 1 should not occur, and from this we can conclude that the Go -Cr -Nb 'flJ film It is speculated that there are multiple crystal layers with different magnetic properties within the structure.

Next, under the same experimental conditions as shown in Fig. 1, Go −
FIG. 2 shows a bisteresis curve in the in-plane direction when a magnetic field of 15 KOe is applied to a recording medium in which Cr-Nb is sputtered to a film thickness of 0.05 μm on a polyimide base. In the figure, there is no magnetization jump in the hysteresis curve as seen in Figure 1, and it can be seen that the Co-Cr-Nb thin film with a film thickness of about 0.05 μm has an approximately uniform crystal structure. be done. In addition to this, from the same figure 0
．． When paying attention to the coercive force HC/ at a film thickness of about 0.05 μm, it is understood that the coercive force HC/ has an extremely small value and the magnetic permeability in the in-plane direction is large. From the above results, the initial layer that first grows near the base by sputtering has a small coercive force HC/, and this initial layer is confirmed by scanning electron micrographs (see the above material). It is considered to be a crystal layer of grain size. In addition, the layer growing above the initial layer has a coercive force HC/ larger than that of the initial layer, and this layer is also a large-grain crystal layer confirmed by scanning electron micrographs. It is believed that there is.

co -Cr in which a small grain size crystal layer and a large grain size crystal layer coexist
The reason why the magnetization jump occurs in the -Nb il film will be described below with reference to FIGS. 3 to 5. As will be described later, the magnetization jump does not occur in all Co--Cr--Nb RIMs with respect to the composition ratio and sputtering conditions. Under certain conditions Co-Cr-N
When a thin film b is formed by sputtering and a hysteresis curve of this thin film is drawn by measurement, a hysteresis curve in which a magnetization jump appears as shown in FIG. 3 is obtained. In addition, a hysteresis curve consisting only of a small-grain crystal layer can be obtained by performing sputtering with a small film thickness (approximately 0.075μ or less, which will be described later) and measuring it (see Section 4). (shown in figure). Furthermore, the large-grain crystal layer is considered to have a uniform crystal structure, and the hysteresis curve shown in Figure 3 is a composite of the hysteresis curve of the small-grain crystal layer and the hysteresis curve of the large-grain crystal layer. Therefore, as shown in FIG. 5, the coercive force HC/ is larger than that of the small-grain crystal layer, and it is thought that a smooth hysteresis curve with no magnetization jump is formed. That is, the third
The presence of magnetization jumps shown in the figure indicates that two layers with different magnetic properties are formed within the same thin film, and therefore the Go -Cr -
It can be seen that two layers with different magnetic properties are formed in the Nb WJ film as well. The coercive force of the large-grain crystal layer is the same as that of Co-Cr-N in which a small-grain crystal layer and a large-grain crystal layer coexist.
b From the hysteresis curve of the thin film, Go with only a small grain size crystal layer
It can be determined from the hysteresis curve obtained by subtracting the hysteresis curve of the -Cr-Nb thin film. The above experimental results prove that when a magnetization jump occurs in the hysteresis curve of Co-Cr-Nb FIJIA, two layers with different magnetic properties are formed.

Then Go -Or -Nb ′fiJ! The magnetic properties of each of the two layers formed during sputtering onto the base of the IA will now be described with reference to FIG. 6 in relation to the thickness dimensions of the Go--Cr--Nb thin film. Figure 6 is Go
-The film thickness of the Cr-Nb thin film is controlled by changing the sputtering time, and the in-plane coercive force HC/ and the perpendicular coercive force 1 (c) and magnetization jump amount σj are respectively drawn for each film thickness. It is something that

First of all, paying attention to the coercive force HC/ in the in-plane direction, when the film thickness dimension is 0.08 μm or less, the value is extremely small (1500
8 or less), and the magnetic permeability in the in-plane direction is considered to be high. In addition, even if the film thickness increases, the coercive force HC
/ does not seem to change much. Also, if we pay attention to the magnetization jump amount σj, we can see that the magnetization jump amount is 0 when the film thickness dimension is 0.
．． It rises sharply at 0.075 μm and forms a clear downward convex parabolic shape for film thicknesses of 0.075 μm or more.

Furthermore, if we pay attention to the coercive force HC in the vertical direction, the coercive force HC
The upper one shows a sharp rise in the film thickness of 0.05 μm to 0.1 μm, and shows a high coercive force of 900 Qe or more when the film thickness is 0.1 μm or more. From these results, the boundary between the small grain size crystal layer and the large grain size crystal layer is located at a film thickness of approximately 0.075 μm, and the small grain size crystal layer with a film thickness of 0.075 μm or less is located in the in-plane direction. and coercive force in the vertical direction) 1c/, H
It is a so-called low coercive force layer with a low coercive force in the vertical direction, and a large grain crystal layer with a film thickness of 0.075 μm or more has a low coercive force H in the in-plane direction, but a low coercive force H in the perpendicular direction.
The layer on C is a so-called high coercive force layer having a very high value, and is a layer suitable for perpendicular magnetic recording. Furthermore, the film thickness dimension that does not cause magnetization jump (0,075 μm or less)
, the coercive force Hc in the in-plane direction and the perpendicular direction is
/, Hc is low, and film thickness larger than this (0,0
75 μm or more), the coercive force Hc in the vertical direction
The top increases rapidly. If a magnetization jump also occurs due to this, it is presumed that two layers with different magnetic properties are formed in the Go-Cr-Nb* film.

Next, Ta is added as a third element to Go-Cr (1 to 10
The same phenomenon occurs in the at% addition range), and the results of the same experiment as in the case of Nb addition described above are shown in the seventh section.
Shown in Figure. Figure 7 shows that the film thickness of the Go-Cr-Ta thin film is controlled by changing the sputtering time, and the in-plane coercive force Hc/, the vertical coercive force HC, and the magnetization jump σj at each film thickness. are drawn respectively. From the same figure, when Ta is added to Go-Cr,
Almost the same results as when Nb was added to Go-Cr were obtained, and the boundary between the small-grain crystal layer and the large-grain crystal layer was approximately 0.075μ.
It is located at the film thickness dimension of m, and the film thickness dimension is 0.075μ
- The following small-grain crystal layers have low coercive force HC/, HC in the in-plane direction and perpendicular direction (both 1700e or less on HC/, )lc), and are so-called low coercive force layers. A large-grain crystal layer with a film thickness of 0.075 μm or more has a low coercive force HC/ in the in-plane direction, but a very high value (750 Qe or more) in the perpendicular coercive force HC.

What should be noted in the above experiment is that the sputtering conditions and the addition of Nb and Ta are set to the above values (Nb: 2 to 2).
10 at%, Ta: 1 to 10 at%), no magnetization jump occurs;

co-Cr-Ta Fill! A small grain size crystal layer and a large grain size crystal layer are also formed (
(See the above document). Go -0r where no magnetization jump occurs
An example of the hysteresis curve of the -Nb thin film is shown in FIG.

FIG. 8(A) is an in-plane hysteresis curve including a small-grain crystal layer and a large-grain crystal layer, and FIG. 8(B) is an in-plane hysteresis curve of only a small-grain crystal layer. Figure 8 (
C) is a hysteresis curve in the in-plane direction of only the large-grain crystal layer. From each figure, residual magnetization M in the in-plane direction of the small-grain crystal layer
Since re/ is larger than the remanent magnetization Mrc/ of the large-grain crystal layer, the remanent magnetization MrA/ including the recrystallized layer is more disadvantageous than when only the remanent magnetization Mr c / of the large-grain crystal layer is anisotropic. The magnetic field Hk becomes smaller. Furthermore, it is known that the small-grain crystal layer has poor orientation (large Δθ50), and also has a large in-plane coercive force HC/, making it unsuitable for perpendicular magnetic recording.

Here, as described above, a Co-Or-Nb@ film and a Co-Cr-Ta film having a small-grain crystal layer and a large-grain crystal layer
'If we consider f1m as a perpendicular magnetic recording medium, Go
-Cr -Nb 1tJll and Go -CI' -
When attempting to perpendicularly magnetize a Ta IF film in the direction perpendicular to the film surface over the entire thickness of the film, the presence of a small-grain crystal layer becomes an extremely disadvantageous factor for perpendicular magnetization (the li-forming jump (This is a disadvantageous factor in the case where a magnetization jump occurs and in the case where a magnetization jump does not occur.) In other words, in a small-grain crystal layer where a magnetization jump occurs, the coercive force Hc / and HC in the in-plane direction and perpendicular direction are both extremely low (17,000 or less), and it is thought that there is almost no perpendicular magnetization in this layer. It will be done. Also, even in a small-grain crystal layer when no magnetization jump occurs, the coercive force 1-1c/ in the in-plane direction is larger than the coercive force HC/ when a magnetization jump occurs, but the perpendicular direction coercive force 1-1c/ Magnetic force H
On C, there is no coercive force sufficient to realize perpendicular magnetic recording, and it is considered that good perpendicular magnetization cannot be achieved. Therefore, even if magnetization is performed perpendicularly to the film surface, perpendicular magnetization in the small-grain crystal layer is hardly achieved, and the perpendicular magnetization efficiency of the magnetic film as a whole is reduced. This effect is noticeable in magnetic heads that include many in-plane components of magnetic flux, such as ring core heads.Also, paying attention to the film thickness dimensions, the above-mentioned Co-Cr-Nb N film and Co-Cr-
When a Ta thin film is made thick enough for practical use as a perpendicular magnetic recording medium (approximately 0.3 μm or less), the thickness of the small-grain crystal layer is approximately constant at 0.1 μm or less (in experiments, the small-grain When the diameter and the film thickness including the large-grain crystal layer are made small, the thickness of the small-grain crystal layer tends to become slightly larger).
The relative thickness of the small grain crystal layer with respect to the thickness of the thin film becomes large, further deteriorating the perpendicular magnetization characteristics.

However, the magnetic properties of the small-grain crystal layer include a small coercive force HC/ in the in-plane direction and a relatively high magnetic permeability. It has characteristics similar to WI (eg, Fe-Ni thin film). In other words, co -Cr-Nbll! and co-
In the mono-i film of Cr-Ta thin i, low coercive force HC/
By using a small-grain crystal layer with a high magnetic permeability layer, which is a so-called underlayer, and using a large-grain crystal layer with a high coercive force HC in the perpendicular direction as a perpendicular magnetization layer, two layers can be formed in a single film structure. It is believed that it is possible to achieve the same functionality as a perpendicular magnetic recording medium with a film structure.

In this point, Go-Cr-Nb WJ film and C0
Changes in magnetic properties and differences in reproduction output when changing the composition ratio of -Cr-Ta 8Il and when changing the thickness dimension of each thin film will be explained below using Figs. 9 to 16. . Figure 9 is a diagram showing various magnetic properties when the composition ratio of the GO-Cr-Nb thin film is changed, and Figures 10 and 11 are diagrams showing the results of perpendicular magnetic recording and reproduction on each thin film shown in Figure 9. This figure shows the relationship between recording wavelength and reproduction output when Note that the thin films shown in FIG. 9 are shown in FIGS. 10 and 11 in a manner that distinguishes them by adding "NO" written at the left end of FIG. 9 to FIGS. 10 and 11. Figure 9 shows that when Nb or Ta is added as a third element to co-Cr, when a magnetization jump occurs, the vertical coercive force HC that contributes to perpendicular magnetization has a high value, but a magnetization jump occurs. When not, the coercive force Hc is a low value. Also, when a magnetization jump occurs, the perpendicular anisotropy field Hk is small, and Mr //MS is Go
- Larger than Czl film. This was considered to be a disadvantageous condition when using a ring core head, which has a large magnetic flux distribution in the in-plane direction. However, each of the above C0-0r"-Nb
and co -Or -Ta m film (hereinafter referred to as Co -Cr-
When Nb thin film and Go-Cr-Ta Film are collectively referred to as Go-Cr-Nb (Ta) thin film)
Looking at the recording wavelength vs. reproduction output characteristics (shown in Figures 10 and 11) when used as a perpendicular magnetic recording medium, it is found that co -Qr-Nb (Ta
') The reproduction output of the H film has a higher magnetization jump than Cg -Cr -Nb ii! The reproduction output is better than that of the film and C9-Czlm, especially in the short wavelength region of the recording wavelength.

In the short wavelength region (region where the recording wavelength is about 0.2 μm to 1.0 μm), Go-Or Fl-MA and Go-Cr-Nb i? with no magnetization jump occur. If
! The playback output is also increasing. However, Go -Cr -Nb (Ta
) film shows a higher reproduction output increase rate than the reproduction output increase rate of each of the above-mentioned thin films, and the Go-Cr-Nb(Ta)Fl film has a magnetization jump.
It can be said that the film is particularly suitable for perpendicular magnetization at short recording wavelengths. In particular, co -C shown in No, I[1, IV
In r-Nb FilH, as shown in Figure 9, although the saturation magnetization MS is more than 10100e/cc smaller than the thin films shown in NO, V, and VI where no magnetization jump occurs, the output in the short wavelength region is low. Good characteristics. In the above-mentioned short wavelength region, the reproduction output curve takes an upwardly convex parabolic shape, but the Go-Cr-Nb thin film in which a magnetization jump occurs in the entire region is GO-Cr.
Co-Cr with thin film and no magnetization jump
-Nb It was possible to obtain a larger reproduction output than the Nl film.

As mentioned above, the improvement in the output characteristics in the short wavelength region is considered to be due to the occurrence of magnetization jump. The in-plane coercive force HC/ of a small-grain crystal layer formed in a magnetic layer where a magnetization jump occurs is equal to the coercive force HC/ of a small-grain crystal layer formed in a magnetic layer where a magnetization jump does not occur. It is smaller.

Here, we will focus on the perpendicular coercive force (LC) of the large-grain crystal layer. As shown in Figure 9 (the raw limit value of magnetization jump is 115
It seems to be a nearby value. In general, the perpendicular coercive force HC of a perpendicular magnetic layer suitable for perpendicular magnetic recording and reproduction is
1 is up to about 1500 Qe, and the in-plane coercive force HC/, in which the small-grain crystal layer in which the magnetization jump occurs appropriately functions as a so-called underlayer, is on average 3.
The lower limit value of 0Qe is thought to be around 1150.

As a result, it is possible to realize a perpendicular magnetic recording medium in which a magnetization jump occurs and, therefore, the reproduction output is particularly good in the short wavelength region. Note that it is possible to adjust the coercive force ratio by appropriately selecting the sputtering conditions.

Next, the reason why the reproduction output is improved in the magnetic layer where the magnetization jump occurs will be explained below.

When the Co-Cr-Nb(Ta)l film is formed as a thin magnetic layer by sputtering, as shown in FIG. A magnetic layer that has magnetic force or is formed becomes a magnetic layer in which a magnetization jump occurs. Therefore, the magnetic flux lines emitted from the magnetic head 4 penetrate the large-grain crystal layer 3 and reach the small-grain crystal layer 2, and within the small-grain crystal layer 2 having low coercive force and high magnetic permeability It is thought that the magnetic flux travels in the in-plane direction and is suddenly absorbed by the magnetic pole portion of the magnetic head 4, causing the large-grain crystal layer 3 to be perpendicularly magnetized. Therefore, the magnetic loop formed by the magnetic flux becomes a horseshoe shape as shown by the arrow in FIG. 12, and the magnetic flux sharply penetrates the large-grain crystal layer 3 at a predetermined perpendicular magnetic recording position, so that the large-grain crystal layer 3 has residual magnetization. A large perpendicular magnetization occurs. If we pay attention to the coercive force HC/ in the in-plane direction of the small grain crystal H2 when a magnetization jump occurs and when no magnetization jump occurs, we can see that the in-plane coercive force HC/ when a magnetization jump occurs as shown in The coercive force HC/ in the direction is smaller than the coercive force HC/ when no magnetization jump occurs. As is well known, in order for the small-grain crystal layer 2 to function as a so-called underlayer, it is desirable to have low coercive force and high magnetic permeability, and therefore Co-C with a magnetization jump has occurred.
It is presumed that r-Nb(Ta)IIM has better reproduction output. Furthermore, since the small-grain crystal layer 2 has a coercive force HC/ that is not completely zero but has a predetermined coercive force, it can be magnetized in accordance with this coercive force. When perpendicular magnetic recording is performed, a plurality of magnets with opposite magnetization directions are alternately formed in the large-grain crystal layer 3, as shown in FIG. 14, corresponding to predetermined bit intervals. Then, a magnetic flux (indicated by the arrow in FIG. 14) is formed in the small-grain crystal layer 2 at the lower ends of the plurality of magnets formed, which connects the lower ends of the magnets formed adjacent to each other. Become magnetized. This eliminates the demagnetizing effect of each adjacent magnet, and this phenomenon is particularly noticeable in perpendicular magnetic recording where the density of adjacent magnets is high, that is, the recording wavelength is small, so it increases the reproduction output in the short wavelength region. Can be done. Furthermore, paying attention to the film thickness of the Go-Cr-Nb(Ta)l film, increasing the film thickness means increasing the thickness of the large-grain crystal layer 3 (small-grain crystal layer 3). (The thickness of the layer 2 is approximately constant), by increasing the thickness, the distance between the magnetic head 4 and the small-grain crystal Ii2 becomes large, and the magnetic flux absorption effect by the small-grain crystal 112 is small, and the 13th As shown by the arrow in the figure, the lines of magnetic force emitted from the magnetic head 4 cross the large-grain crystal layer 3 without reaching the small-grain crystal layer 2, and are sucked into the magnetic pole of the magnetic head 4. Therefore, the magnetization in the perpendicular direction is dispersed and weak, and good perpendicular magnetization is not achieved.However, Co - Cr - Nb (T
a) When the thickness of the thin film is made small, the distance between the magnetic head 4 and the small-grain crystal layer 2 becomes small, and the effect of sucking the magnetic flux by the small-grain crystal 1t2 becomes large, and the magnetic flux emitted from the magnetic head 4 becomes The magnetic flux reliably advances to the small-grain crystal layer 2 and forms the above-mentioned horseshoe-shaped magnetic loop. That is, since the magnetic flux that contributes to perpendicular magnetization is an extremely sharp horseshoe-shaped magnetic field, it is thought that residual magnetization is large and good perpendicular magnetization is performed. That is, G
The smaller the thickness of the o -Cr-Nb(Ta)I film (the thinner the recording medium is), the better perpendicular magnetization can be achieved, which allows for better perpendicular magnetization between the magnetic head 4 and the magnetic head 4. It is possible to realize a thin recording medium with good contact (according to the inventor's experiments, the film thickness is 0.1 μ- to 0.
High output could be maintained up to dimensions of about 63 μm). In addition, as mentioned above, the Go-Cr-Nb (Ta) thin film that forms the layer with high coercive force and the layer with resistive magnetic force is formed by continuous sputtering. There is no need to change conditions or replace the target, and Co-C
The in-plane coercive force HC/ has a large grain size, which can facilitate the formation process of the r-Nb(Ta) thin film, shorten the sputtering time, and manufacture perpendicular magnetic recording media at low cost and with mass productivity. Since the value is not extremely small compared to the coercive force Hc of the crystal layer 3, good perpendicular magnetic recording and reproduction can be performed without generating impulsive Barkhausen noise.

Effects of the Invention As described above, according to the perpendicular magnetic recording medium of the present invention, in a perpendicular magnetic recording medium having a magnetic layer formed of an upper layer and a lower layer, the magnetic layer of the upper layer in the perpendicular direction is magnetized. This becomes a magnetic layer with jumps, and the magnetic flux emitted from the magnetic head easily enters the lower layer with low coercive force and travels horizontally, then suddenly and sharply penetrates the upper layer with high coercive force at the magnetic pole of the magnetic head. Because the magnetic head is absorbed into the magnetic pole of the magnetic head, strong residual magnetization occurs in the upper layer, making it possible to perform perpendicular magnetic recording and reproduction that can achieve high reproduction output.In addition, excellent perpendicular magnetization is achieved especially when the recording wavelength is short. It is possible to obtain good reproduction output, and the lower layer has a magnetization jump, that is, it has a small coercive force in the in-plane direction and has high magnetic permeability, so it functions reliably as a so-called underlayer. At the same time, its coercive force is not extremely small compared to the coercive force of the upper layer, so it has the advantage of being able to perform good perpendicular magnetic recording and reproducing without generating impulsive Barkhausen noise. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a hysteresis curve of a Go-Cr-Nb thin film, which is a magnetic film of an embodiment of a perpendicular magnetic recording medium according to the present invention, and FIG. 2 is a diagram showing a hysteresis curve of a small-grain crystal layer. Figures 3 to 5 are diagrams for explaining the reason why magnetization jump occurs, and Figure 6 is Co-Cr-Nb.
Figure 7 shows that WIWA has a two-layer structure and the magnetic properties of each layer.
The figure shows an example of the hysteresis curve of a Co-Cr-Nb thin film with no magnetization jump, and Figure 9 shows an example of the hysteresis curve of a Co-Cr-Nb thin film with no magnetization jump.
- A diagram showing various magnetic properties of a Co -Cr -Ta N film in comparison with magnetic properties of a Co -Cr -Nb Film and a Co -Cr 31 film in which no magnetization jump occurs,
10 and 11 are diagrams showing the relationship between recording wavelength and reproduction output when performing perpendicular magnetic recording and reproduction on each of the thin films shown in FIG. Figure 13 is a diagram showing the magnetic loop formed by the magnetic flux when the thickness of the recording medium of the present invention is increased, and Figure 14 is a diagram showing the magnetic loop formed by the magnetic flux when the thickness of the recording medium of the present invention is increased. FIG. 3 is a diagram for explaining magnetic flux that communicates between lower end portions of a plurality of magnets formed in a crystal layer and magnetized in a large-grain crystal layer. DESCRIPTION OF SYMBOLS 1...Base, 2...Small grain size crystal layer, 3...Large grain size crystal layer, 4...Magnetic head. Patent Applicant: Victor Company of Japan Co., Ltd. (Figure 2, Figure 7)

Claims (1)

[Claims] For a perpendicular magnetic recording medium having a magnetic layer formed by an upper layer and a lower layer, the coercive force in the perpendicular direction of the upper layer is expressed as H_c_
⊥, and the coercive force in the in-plane direction of the lower layer is H_c_■, then the value of the ratio (H_c_■)/(H_c_⊥) is 1/50.
A perpendicular magnetic recording medium, characterized in that the perpendicular magnetic recording medium is selected such that ≦(H_c_■)/(H_c_⊥)≦1/5.