JPS61204822A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To perform good vertical magnetic recording and reproducing by specifying the squareness ratio in the plane direction of a hysteresis loop in the plane of a magnetic layer of a vertical magnetic recording medium where a layer of low coercive force and a layer of high coercive force on said layer are formed. CONSTITUTION:The magnetic layer of the vertical magnetic recording medium which consists of a magnetic material and is formed with a layer 2 having an especially low coercive force and a layer 3 having a high coercive force on the layer 2 is so constituted that the magnetic layer has the plane hysteresis characteristic where the squareness ratio in the plane direction of the plane hysteresis loop is >=0.2. The magnetic material where Nb or/and Ta are added to Co and Cr is sputtered as a target on a polyimide substrate of a base to obtain the vertical magnetic recording medium.

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 that can improve perpendicular magnetic recording and reproducing characteristics.

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, as recording density increases, the demagnetizing field increases and decreases (6), which is known to have an adverse effect on high-density recording.In recent years, magnetic recording media have been developed to eliminate the above-mentioned adverse effects. A perpendicular magnetic recording method has been proposed in which the magnetic layer is magnetized in the perpendicular direction. According to this method, as the recording density increases, the demagnetizing field becomes smaller, and theoretically, good high-density recording is possible with no decrease in residual magnetization. can be done.

Conventionally, as a perpendicular magnetic recording medium used in this perpendicular magnetic recording system, a co-cr film was formed on a base film by sputtering. As is well known,
The C0-Cr film has a relatively high saturation magnetization (Ms),
It is known that it is an extremely promising material for perpendicular magnetic recording media 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). There is. However, as mentioned above, Co
- 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.

Moreover, in order to solve the above-mentioned problem, a layer with a small high magnetic permeability layer (i.e., coercive force) 1c, which is a so-called underlayer, is provided between the GO-Cr film and the base film.

For example, Ni-Fe) 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 and strong distribution. There was a perpendicular magnetic recording medium with a configuration capable of perpendicular magnetization.

Problems to be Solved by the Invention However, the above-mentioned conventional perpendicular magnetic recording medium 9, for example, Co-C
When recording on a single-layer medium with a ring core head, the magnetic field has a considerable component in the in-plane direction, so the magnetization changes in slope and size during recording. In order to maintain the magnetization perpendicularly, perpendicular magnetic recording media have a high perpendicular anisotropy field (Hk),
It was necessary to suppress the saturation magnetization (MS) to a certain small value. In addition, in order to achieve high reproduction output, it was necessary to increase the perpendicular coercive force (1'' C) and to increase the thickness of the perpendicular magnetic recording medium. In addition, if the thickness 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 magnetic head of the perpendicular magnetic recording medium) will become poor, which may damage the perpendicular magnetic recording medium. There was a problem in that good perpendicular magnetic recording and reproduction could not be achieved due to adverse effects on the magnetic head.

In addition, in the case of a perpendicular magnetic recording medium with a two-layer structure in which a high magnetic permeability layer is formed as a backing layer in addition to a Co-Cr film, a Co-C
Since the coercive force Hc of the high magnetic permeability layer was extremely small (10Q8 or less) compared to the coercive force Hc of the r film (700 Oe or more), there was a problem in that impulsive Barkhausen noise was generated.

Therefore, in the present invention, we focused on the fact that when coated with a magnetic material, the magnetic layer is formed into two layers with different coercive forces, and by actively utilizing each layer with different coercive forces for perpendicular magnetic recording. It is an object of the present invention to provide a perpendicular magnetic recording medium that solves the above problems.

Means for Solving the Problems In order to solve the above problems, in the present invention, the magnetic layer made of one magnetic material has a layer having a particularly low coercive force and a layer having a high coercive force formed thereon. The magnetic layer of the perpendicular magnetic recording medium is configured to have an in-plane hysteresis characteristic in which the squareness ratio in the in-plane direction in the in-plane hysteresis loop is 0.2 or more.

Embodiment A perpendicular magnetic recording medium according to the present invention (hereinafter simply referred to as a recording medium) is made of a polyimide substrate which serves as a base, and at least one of cobalt (Go), chromium (Or), niobium (Nb), and tantalum (Ta). It can be obtained by sputtering a magnetic material obtained by adding the above as target layer 1-.

Conventionally, when sputtering metal etc. (e.g. Co-Or alloy) onto a base layer, the formed thin film does not form the same crystal structure in the direction perpendicular to the film surface, but instead forms a very thin part near the base layer. 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.

G1. Judy: ”INITIAL
1-AYFRFFECT IN Co-
CRFILMS”.

IEEE Trans, , VOL, MAG-20°N
O, 5, SEPTEMBER1984, P 774~P
175 or William G, l-1aine
s: ”VSMPROFILING OF Co
CrFLMs: A NEW ANALYTIC
A+, -TFCHNIQUF”IEEE Tran
sl, VOL, MAG-20, No, 5. SEPTEM
BER1984, p 812-p 814). The present inventor focused on the above-mentioned point of view and sputtered various metals based on Go-Or gold alloy and added a third element to it, and created a crystal layer with a small grain size and a large crystal layer formed on the soil. As a result of measuring the physical properties of the grain-sized crystal layer, we 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. I understand. 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.

Below, the results of an experiment conducted by the present inventor in which the coercive force of a small grain crystal layer formed by sputtering and a large grain crystal layer were measured will be described in detail. Co-CrR9 film, co-0r
When sputtering the -Nb I 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 Magne 1 ~ Ron sputtering * Sputtering method Continuous sputtering. Preliminary 11 atm 1×1O-6T
After exhausting to orr, Ar gas was introduced and I
Torr *Base polyimide (thickness 20μl11) *To composite targetera 1 with a small piece of N+1 or Ta placed on target C0-0r alloy *Distance between target substrates 10mm The magnetic properties of the thin film were measured using a vibrating sample magnetometer. (manufactured by Riken Denshi,
The composition of the thin film was measured using an energy dispersive microanalyzer (manufactured by KEVEXa, hereinafter 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 CoCr (2 to 10a
The same phenomenon occurs in the t% 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 figure, it can be seen that the hysteresis curve suddenly rises irregularly (indicated by arrow A in the figure) at a portion where the in-plane coercive force (indicated by the symbol HC/) is near zero, and a so-called magnetization jump occurs.

Sputtered Co-Cr-Nb'114
If we assume that the film always undergoes uniform crystal growth during sputtering, the magnetization jump shown in Figure 1 should not occur, and this suggests that there are multiple crystal layers with different magnetic properties in the GO-0r-Nb thin film. It is assumed that there is.

Subsequently, under the same experimental conditions as shown in Fig. 1, Co −
FIG. 2 shows a hysteresis curve in the in-plane direction when a magnetic field of 15 KOe is applied to a recording medium in which r-Nb is sputtered to a film thickness of 0.05 μm on a polyimide base. In the same figure, there is no magnetization jump in the hysteresis curve as seen in Figure 1, and the Go-0r-Nb thin film with a thickness of about 0.05 μm is a substantially uniform crystal.
It is understood that there are 1. In addition to this, from the same figure 0
．． When paying attention to the coercive force IHC/ at a film thickness of about 0.05 μm, it can be seen that the coercive force HC/ is an extremely small value, indicating that the magnetic permeability in the in-plane direction is about 100%.

From the above results, the coercive force HC/ of the initial m-layer that first grows in the vicinity of the base by sputtering is small, and this initial layer grows in the vicinity of the base, as confirmed by scanning electron micrographs (see the above document). This is thought to be a crystal layer with small grain size. In addition, the layer growing above the initial layer has a coercive force HC/a larger coercive force CI of the initial layer, and this layer is also a large-grain crystal layer confirmed by scanning electron micrographs. It is thought that.

Co-Or in which small grain size crystal layer and large grain size crystal layer coexist
-The third reason why magnetization jump occurs in NbH film
This will be described below using FIGS. Furthermore, as described later,
Magnetization jumps do not occur for all Co-Cr-Nb thin films with respect to composition and sputtering conditions. A Go-Cr-Nb thin film was formed by sputtering under predetermined conditions, and the hysteresis curve of this thin film was drawn by measurement as shown in Figure 3.
The hysteresis curve appears. 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 0.075 μm or less, which will be described later) and measuring it (Fig. 4). ). Furthermore, the large-grain crystal layer is considered to have a uniform crystal pattern, 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. In other words, the existence of the magnetization jump shown in FIG. 3 indicates that two layers with different magnetic properties are formed within the same thin film, and therefore the Co-Cr shown in FIG. -Nb
It is obvious that the thin film also has two layers with different magnetic properties. The coercive force of the 4r large-grain crystal layer is Co-Cr-Nb in which the small-grain crystal layer and the large-grain crystal layer coexist.
From the hysteresis curve of the thin film, only a small crystal layer of Co
It can be determined from the hysteresis curve obtained by subtracting the hysteresis curve of the Cr--Nb thin film. Each of the above experiments! The results prove that when a magnetization jump occurs in the hysteresis curve of a co -Cr -Nb thin film, two layers with different magnetic properties are formed.

Next, using FIG. 6, the magnetic properties of each of the above two layers formed during sputtering on the base of the Co-Gr-Nb thin film are related to the thickness dimension of the Go-Or-NllN film. This will be explained below. Figure 6 shows Co-Cr
- The film thickness of the Nb thin film is controlled by changing the sputtering time, and the in-plane coercive force 1-1c/, the perpendicular coercive force 1-1c, and the magnetization jump ■σj at each film thickness are set in the groove. It was there.

First of all, paying attention to the antimagnetic quadratic IC/ in the in-plane direction, it is an extremely small value of 180 Oe or less when the film thickness is 0.15 μm or less, and it is considered that the magnetic permeability in the in-plane direction is high. Also, even if the film thickness is human, the coercive force HC
'/ doesn't seem to change much. Further, when paying attention to the magnetization jump amount σj, the magnetization jump amount rises rapidly when the film thickness dimension is 0.075 μm, and draws a smooth downwardly convex parabolic shape at a film thickness of 0.075 μm or more. Furthermore, if we pay attention to the coercive force Hc in the vertical direction, the coercive force 1
-1c soil suddenly becomes 1 when the film thickness is 0.05μm to 01μm.
Starting from 80 Oe, a film thickness of 0.1 μm or more exhibits a high coercive force of 900 Oe or more. From these results, the boundary between the small-grain crystal layer and the large-grain crystal layer is located at the film thickness of approximately 0.075 μm, and the small-grain crystal layer with a film thickness of 0.075 μm or less is located in the in-plane direction and The coercive force HC/ and 1-1c in the vertical direction are both low, approximately 180 Oe or less, forming a so-called resistive magnetic layer, and the film thickness is 0.
．． The large grain size crystal layer of 075 μm or more has a coercive force H in the in-plane direction.
Although c/ is low at approximately 180 Oe or less, the coercive force HC1 in the vertical direction is 20 near the film thickness dimension where the magnetization jump occurs.
The film thickness rapidly increases from 0.008 to 900 Oe, and then gradually increases as the thickness increases, becoming a so-called high coercive force layer, which is suitable for perpendicular magnetic recording. In terms of dimensions (0,075 μm or less), antimagnetic JHC in the in-plane direction and perpendicular direction
/ and Hc J- are both as low as 180 Oe or less, and when the film thickness is larger than this (0,075 μm or more), the coercive force HCI in the vertical direction rapidly increases.

If this also causes a magnetization jump, Go
It is presumed that two layers with different magnetic properties are formed in the -Cr-Nb thin film.

Next, Ta is added as a third element to Co-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.
As shown in the figure. Figure 7 shows that the thickness of the Co-Cr-Ta thin film is controlled by changing the sputtering time, and the coercive force in the in-plane direction 1-IC/, and the coercive force in the perpendicular direction j1-ICJLo at each film thickness. Iti conversion jump σj
are drawn respectively. From the same figure, when Ta is added to CO-Cr, almost the same results as when Nb is added to co-Cr are obtained, and the boundary between the small-grain crystal layer and the large-grain crystal layer is approximately 0.075 μm. The small-grain crystal layer with a thickness of 0.075 μm or less has a coercive force in the in-plane direction and the perpendicular direction (1c/), and the Hc soil has a low (1c/)
"c/, HCl are both 170 Oe or less), so-called resistive magnetic layer, and the film thickness is 0.075 μm.
Although the above-mentioned large-grain crystal layer has a low coercive force HC/ in the in-plane direction, the coercive force 1-1c in the perpendicular direction rises from 20,000 to 750 Oe or more near the film thickness dimension where the magnetization jump occurs, and even after that, the film thickness dimension This is a so-called high coercive force layer that gradually increases as the value increases.

What should be noted in the above experiment is that the sputtering conditions and the amounts of Nb and Ta added were set to the values described above (Nb: 2 to 10
at%, Ta: 1 to 10 at%), no magnetization jump occurs, but a magnetization jump occurs in the 4T CO~Or-NtztD film.

Co-Cr-Ta'? Even in the a film, a small grain size crystal layer and a large grain size crystal layer are formed (see the above document). co −Or − where no magnetization jump occurs
An example of the hysteresis curve of the Nb WJ 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. FIG. 8(C) is a hysteresis curve in the in-plane direction of only the large-grain crystal layer. From each figure, the residual magnetization MrB / in the in-plane direction of the small grain crystal layer is larger than the residual magnetization Mr c / of the large grain crystal layer, so the residual magnetization Mr A / including both crystal layers is larger than the residual magnetization Mr A / of the large grain crystal layer. The residual magnetization M r (:) of the crystal layer is less favorable than that of / only, and the anisotropy magnetic field Hk is smaller than 4. It is also known that the small-grain crystal layer has poor orientation (8050 is large). Moreover, the coercive force HC/ in the in-plane direction is large, making it unsuitable for perpendicular magnetic recording.

Here, when considering the Co-Cr-Nb thin film and Co-Cr-Ta thin film having the small-grain crystal layer and the large-grain crystal layer as a perpendicular magnetic recording medium as described above, CO-0r-N
When attempting to create perpendicular magnetization in the b thin film and the Go-Cr-Ta '4 film over the entire film thickness in the direction perpendicular to the film surface, the existence of a small-grain crystal layer is extremely disadvantageous for perpendicular magnetization. (It becomes a disadvantageous factor when a magnetization jump occurs and when a magnetization jump does not occur). That is, in a small-grain crystal layer where a magnetization jump occurs, both the coercive force HC/ and HC in the in-plane direction and the perpendicular direction are extremely low, and it is considered that there is almost no perpendicular magnetization in this layer. In addition, even in a small-grain crystal layer when no magnetization jump occurs,
The coercive force IHC/ in the in-plane direction is larger than the coercive force HC/ when a magnetization jump occurs, but the coercive force in the perpendicular direction is not large enough to realize perpendicular magnetic recording. It is considered that good perpendicular magnetization cannot be achieved without this. 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 remarkable in a magnetic head such as a ring-ahead type that includes a large in-plane component of magnetic flux. Also, paying attention to the film thickness dimension, the film thickness dimension T (approximately 0
．． 3 μm or less), the thickness dimension of the small grain crystal layer is 0.
．． Since it is approximately constant at 15 μm or less (in experiments, the thickness of the small-grain crystal layer tends to become slightly larger when the film thickness including the small-grain crystal layer and the large-grain crystal layer is made small), The relative thickness dimension of the small grain size crystal layer with respect to the film thickness dimension 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. (For example, Fe-1id film). That is, Co-Cr-Nb thin film and Go-0r
- In a single Ta thin film, a small-grain crystal layer with low coercive force HC/ is used as a high permeability layer, which is a so-called backing layer, and a large-grain crystal layer with high coercive force HC on vertical direction is used. It is thought that by using it as a perpendicular magnetic layer, it is possible to realize the same function as a perpendicular magnetic recording medium with a double-layer structure in a single-layer structure.

In view of this point, Co-cr-Nb thin film and G.

The changes in magnetic properties and differences in reproduction output when the composition ratio of the -0r-Ta thin film is changed and the thickness dimension of each thin film is changed will be explained below using FIGS. 9 to 16. . Figure 9 is a diagram showing various magnetic properties when the composition ratio and film thickness dimensions of the Co-Cr-Nb thin film are changed, and Figures 10 (A) to (E) are diagrams for each thin film shown in Figure 9. This is a drawing of the in-plane hysteresis curve. From both figures, even when Nb is added as a third element to CO-Cr,
Magnetization jump (arrow B in Fig. 10 (A) and (D)).

When magnetization jump (indicated by C) occurs, the perpendicular coercive force HC1, which approaches perpendicular magnetization, takes a high value, but when no magnetization jump occurs, the coercive force HC-t takes a low value. In addition, the thickness of the Go-Cr-Nb Wl film is small (about 1/2 h in the data), but the coercive force T-LC soil has a high value.In addition, when a magnetization jump occurs, The coercive force HC/ in the in-plane direction of the small grain crystal layer is approximately 180 Oe
In the following, the coercive force 11C in the perpendicular direction of the large grain crystal layer is approximately 200 Oe or more, the perpendicular anisotropy magnetic field Hk is small, and the squareness ratio Mr //MS in the in-plane direction is approximately the same -
The film thickness is larger than that of a Co--Cr thin film, and as the film thickness δ becomes thinner, the lower limit becomes 02, and the value gradually increases. That is, the magnetization jump occurs in a platform in which the in-plane squareness ratio Mr//Ms of the magnetic film is 0.2 or more. This was considered to be a disadvantage when using a ring core head, which has a large magnetic flux distribution in the in-plane direction. However, when looking at the recording wavelength-reproducing output characteristics (shown in FIG. 11) when each of the above Go-Cr-Nb thin films is used as a perpendicular magnetic recording medium, the Go-Cr-Nb RR exhibits a chemical jump of 14. The reproduction output of CoCrNb has no magnetization jump.
The reproduction output is better than that of H film and Go-Cr thin film.
20, and this is particularly noticeable in the short recording wavelength region. In the short wavelength region (region where the recording wavelength is about 0.2 μm to 1.0 μm), the reproduction output increases even in the co-Cr thin film and the co-Or-Nb thin film in which no magnetization jump occurs. However, the co -Or -Nbl film in which a magnetization jump has occurred shows a higher rate of increase in reproduction output than that of each of the above-mentioned thin films. 0r-Nb
It can be said that thin films are particularly suitable for perpendicular magnetization at short recording wavelengths. In the above-mentioned short wavelength region, the reproduction output curve takes an upwardly convex parabolic shape, but the Co-Cr-Nb thin film in which the magnetization jump occurs in the entire region is Go-
Cr thin film and Go-Cr without magnetization jump
- It was possible to obtain a larger reproduction output than the Nb thin film. Note that (:, o -Cr -Ta thin film also has Co -C
Almost the same results as the r-Nb thin film were obtained. Figure 12 shows C0-0r-T for C0-Cr thin films with different film thickness dimensions.
13(A) to 13(C) show the in-plane direction hysteresis curves formed by each thin film, and
Figure 4 shows the recording wavelength vs. reproduction output characteristics.

It is thought that the above-mentioned visual image occurs due to the following reasons. Co-Cr-Nb thin film and Co-Cr-Ta thin film (hereinafter referred to as Co-Cr-Nb thin film) (:, o -0r
-Ta thin film is collectively called Co -Cr -Nb(Ta)t
(referred to as tI film) is made by sputtering. At the time of formation, as shown in FIG. 15, a two-layer structure is formed, including a small-grain crystal layer 2 having a resistive magnetic force near the base 1 and a large-grain crystal layer 3 having a high coercive force especially in the vertical direction above it. 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 the magnetic flux is distributed in a plane within the small-grain crystal layer 2, which has a resistive magnetic force and high magnetic permeability. It is considered that the large-grain crystal M3 is perpendicularly magnetized as the magnetic flux is rapidly absorbed by the magnetic pole portion of the magnetic head 4 as it progresses inward. Therefore, the magnetic loop formed by the magnetic flux becomes a horseshoe shape as shown by the arrow in FIG.
Perpendicular magnetization with large residual magnetization occurs. If we pay attention to the coercive force 1''c/ in the in-plane direction of the small-grain crystal layer 2 when a magnetization jump occurs and when it does not occur, we can see that the in-plane hysteresis occurs as shown in FIGS. 9 and 12. When the in-plane squareness ratio of the loop is 02 or more, the coercive force HC/ in the in-plane direction when the in-plane hysteresis characteristic is shown, that is, when a magnetization jump occurs, is the same as the lifting platform where no magnetization jump occurs. The value is smaller than the coercive force HC/. 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.
It is presumed that the -Cr-Nb (Ta) thin film has better reproduction output. In the experiments conducted by the present inventor, the coercive force 1-1c/ in the in-plane direction of the small-grain crystal layer 2 is 180 Oe or less, and the coercive force 1-1c/ in the vertical direction of the large-grain crystal layer B3 is taken into account, considering the influence of measurement errors, etc. When the coercive force HCf was 200 Oe or more, the reproduction output had a good value. Go again
Focusing on the thickness of the -Cr-Nb(Ta) thin film,
Increasing the film thickness means increasing the thickness of the large-grain crystal layer 3 (the thickness of the small-grain crystal layer 2 is approximately constant), and increasing this. As a result, the distance between the magnetic head 4 and the small-grain crystal layer 2 becomes large, and the magnetic flux absorption effect by the small-grain crystal layer 2 is slight, and the lines of magnetic force emitted from the magnetic head 4 are small particles, as shown by the arrows in FIG. It crosses the large-grain crystal layer 3 without reaching the large-grain crystal layer 2 and is sucked into the magnetic pole of the magnetic head 4. Therefore, the magnetization in the perpendicular direction is dispersed and weak, and good 11 perpendicular magnetization is not performed. However, if the thickness of the CO-Cr-Nb (Ta) thin film is made small, the magnetic head 4 and the small-grain crystal layer 2
The distance becomes small, and the effect of sucking the magnetic flux by the small-grain crystal layer 2 is strong, so that the magnetic flux emitted from the magnetic head 4 reliably advances to the small-grain crystal layer 2, forming 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 achieved. That is, GO-Cr-N
It is better to reduce the film thickness of the b(Ta) thin film (recording medium
24) can achieve better perpendicular magnetization, which makes it possible to realize a thin recording medium that has good contact with the magnetic head 4 (according to experiments conducted by the present inventor). High output could be maintained up to a film thickness of about 0.1 μm to 0.3 μm). Furthermore, a small grain size crystal layer 2
The coercive force HC/ in the in-plane direction is approximately 180 Oe or less, and the coercive force of the large grain crystal layer 3 is above -1c (approximately 200 Oe or more)
Since the value is not extremely small, 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, the magnetic layer made of one magnetic material is a perpendicular magnetic recording medium in which a layer having a particularly low coercive force and a layer having a high coercive force are formed thereon. By configuring the magnetic layer of the magnetic recording medium to have an in-plane hysteresis characteristic in which the squareness ratio in the in-plane direction in the in-plane hysteresis loop is 0.2 or more, the magnetic layer has an in-plane squareness ratio of 0.2 or more. Since it is a magnetic layer with a type ratio of 02 or more and a magnetization jump occurs, a layer with low coercive force has small coercive force in the in-plane direction and high magnetic permeability, and is reliable as a so-called underlayer. Therefore, the magnetic flux emitted from the magnetic head penetrates the layer with high coercive force, easily enters the layer with low coercive force, and after traveling in the horizontal direction, suddenly and sharply increases the magnetic flux at the magnetic pole of the magnetic head. Because it penetrates the layer with high coercive force and is absorbed by the magnetic pole of the magnetic head, strong residual magnetization occurs in the layer with high coercive force, making it possible to perform perpendicular magnetic recording and reproduction that can achieve high reproduction output. The reproduction output has particularly excellent characteristics when the recording wavelength is short, and particularly good reproduction output can be obtained in the short wavelength region, and the coercive force of the layer with low coercive force is equal to the coercive force of the layer with high coercive force. Since the value is not extremely small, it has the advantage that good perpendicular magnetic recording and reproduction can be performed without generating impulsive Barkhausen noise.

[Brief explanation of the drawing]

Figure 1 shows I of the perpendicular magnetic recording medium according to the present invention.
il +1 film Go -Cr -Nb thin film not=
,i. Figure 2 is a diagram showing the hysteresis curve of a small-grain crystal layer, Figures 3 to 5 are diagrams for explaining the reason why magnetization jumps occur, and Figure 6 is a diagram showing the hysteresis curve of a small-grain crystal layer.
Figure 7 shows the two-layer structure of the r-Nb thin film and the magnetic properties of each layer. Figure 7 is a diagram showing the two-layer structure of the Co-, Cr-Ta thin film and the magnetic properties of each layer. ,
Figure 8 shows Co Cr with no elbow A7 bump.
- Diagram showing an example of a hysteresis curve of a Nb thin film, No. 9
The figure shows various magnetic properties when the composition ratio and film thickness of the CO-Cr thin film and CO-Cr-Nb thin film are changed. Figure 10 shows the hysteresis curve of each thin film shown in Figure 9. Figure 11 shows Co -Or -Ntl
Figure 12 shows the relationship between recording wavelength and reproduction output when perpendicular magnetic recording and reproduction is performed on a lJ film and a CO-Cr thin film. A diagram showing the magnetic characteristics, Figure 13 is the first
Figure 1 shows the hysteresis curves of each thin film shown in Figure 2.
Figure 4 shows Co84.8 Cr13.4 Ta1.8i1 in Figure 12 = 27-
1 film and C081Cr19it! Membrane (δ-0, 10ft
Fig. 15 shows the relationship between the recording wavelength and the reproduction output when perpendicular magnetic recording and reproduction is performed. (Figure 16 shows a 111! loop formed by the magnetic flux when the thickness of the recording medium of the present invention is increased. 1...Base, 2...Small grain size crystal layer, 3...Large grain size crystal layer, 1...Magnetic head.

Claims (3)

[Claims] (1) A perpendicular magnetic recording medium in which a magnetic layer made of a magnetic material has a layer having a particularly low coercive force and a layer having a high coercive force formed thereon, the magnetic layer having an in-plane hysteresis. A perpendicular magnetic recording medium characterized by having an in-plane hysteresis characteristic in which a squareness ratio in an in-plane direction in a loop is 0.2 or more. (2) The perpendicular magnetic recording medium according to claim 1, wherein the layer having particularly low coercive force has an in-plane coercive force of 180 Oe or less. (3) The perpendicular coercive force of the layer having high coercive force is 20
Claim 1 characterized in that it is 0 Oe or more.
The perpendicular magnetic recording medium according to item 1 or 2.