JPH0628091B2 - Perpendicular magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium capable of improving perpendicular magnetic characteristics.

2. Description of the Related Art Generally, in order to record / reproduce on / from a magnetic recording medium by using a magnetic head, the magnetic layer of the magnetic recording medium is magnetized in the longitudinal direction (in-plane direction) of the magnetic recording medium and recorded. The thing to reproduce is general-purpose. However,
According to this, it is known that the demagnetizing field increases as the recording density increases, and the demagnetizing action adversely affects the high density recording. Therefore, in recent years, as a means for eliminating the above-mentioned adverse effects, a perpendicular magnetic recording system has been proposed in which the magnetic layer of the magnetic recording medium is magnetized in the perpendicular direction. According to this, as the recording density is improved, the demagnetizing field becomes smaller, and theoretically good high density recording in which the residual magnetization does not decrease can be performed.

Conventionally, as a perpendicular magnetic recording medium used in this perpendicular magnetic recording system, there is one in which a Co-Cr film is formed on the base film by sputtering. As is well known, C
The o-Cr film has a relatively high saturation magnetization (Ms) and an easy axis of magnetization perpendicular to the film surface (that is, the coercive force Hc ⊥ in the direction perpendicular to the film surface is large). It is known that the recording medium is an extremely promising material. However, as described above, Co-C
In the case of a perpendicular magnetic recording medium having a single r film structure, the magnetic flux cannot be concentrated at a predetermined magnetic recording position on the perpendicular magnetic recording medium (especially when a ring core head is used). The recording medium has a problem that the distribution is sharp and strong perpendicular magnetization cannot be performed.

In order to solve the above problems, a high magnetic permeability layer (that is, a layer having a small coercive force Hc, that is, a so-called backing layer, for example, Ni-Fe) is provided between the Co-Cr film and the base film.
Is formed separately to form a two-layer structure, and the magnetic flux spreading in the high-permeability layer is concentrated toward the magnetic pole of the magnetic head at a predetermined magnetic recording position and is absorbed, so that a sharp distribution and strong perpendicular magnetization can be performed. A perpendicular magnetic recording medium having a structure has been obtained.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the above-mentioned conventional perpendicular magnetic recording medium such as Co-C
r When recording on a 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 keep the magnetization perpendicular, the perpendicular magnetic recording medium has a high perpendicular anisotropy field (Hk), and the saturation magnetization (Ms) needs to be suppressed to a small value to some extent. Further, in order to realize a high reproduction output, it was necessary to increase the coercive force (Hc _⊥ ) in the vertical direction and increase the thickness of the perpendicular magnetic recording medium. When the thickness is large, the so-called hit of the magnetic head of the perpendicular magnetic recording medium (sliding contact condition at the sliding contact portion between the perpendicular magnetic recording medium and the magnetic head) is deteriorated, and the perpendicular magnetic recording medium is damaged. There is a problem that the magnetic head is adversely affected and good perpendicular magnetic recording / reproduction cannot be performed.

In addition, in the case of a perpendicular magnetic recording medium having a two-layer structure in which a high magnetic permeability layer is used as a backing layer in addition to the Co-Cr film, Co-C
Since the coercive force Hc of the high-permeability layer was extremely small (10 Oe or less) with respect to the coercive force Hc (700 Oe or more) of the r film, there was a problem in that shock-induced bulk Ausen noise was generated. . In addition to this, in order to obtain a perpendicular magnetic recording medium having a two-layer structure, first, Fe-Ni / amorphous or the like is coated on the base film by spattering under predetermined conditions suitable for forming a high magnetic permeability layer, and then, To Co-C
It is necessary to coat Co-Cr by spattering under a predetermined condition suitable for forming the r film, and it is necessary to change the spattering condition and the target every time each layer is formed. There was a problem that it became complicated and the mass productivity was poor.

Therefore, an object of the present invention is to provide a perpendicular magnetic recording medium which solves the above problems by selecting the ratio of the coercive force of each layer of the magnetic layers 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 by an upper layer and a lower layer,
When the vertical coercive force of the upper layer is Hc _⊥ and the in-plane coercive force of the lower layer is Hc, The value of Was selected.

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

Conventionally, when a metal or the like (for example, Co-Cr alloy) is sputtered on a base, the thin film formed does not form the same crystal structure in the vertical direction on the film surface, but an extremely thin portion near the base. First, a small crystal grain first crystal layer was formed, and then a large crystal grain second crystal layer was formed on top of it, by various experiments (eg, scanning electron microscope photography). (Edward R. Wuori and Professor JHJ
udy: "INITIAL LAYER EFFECT
IN CO-OR FILMS ", IEEE Tran
s., VOL. MAG-20, No.5, SEPTEMBE
R 1984, P 774-P 775 or William G. Haine
s: "VSMPROFILING OF Co CrFIL
MS: A NEW ANALYTICAL TECHN
IQUE "IEEE Trans., VOL, MAG-2
0, No. 5, SEPTEMBER 1984, P 812 to P 81
Four). The present inventor pays attention to the above point of view, and based on a Co--Cr alloy, and by various sputtering of a metal to which a third element is added, a crystal layer having a small grain size and a large grain formed on the crystal layer are formed. As a result of measuring the physical properties of the crystal layer with a large diameter, especially when Nb or Ta is added as the third element, the coercive force of the small grain crystal layer is much smaller than that of the large grain crystal layer. Wakatsuta. The present invention is characterized in that the small grain size crystal layer having the low coercive force is used as the high magnetic permeability layer and the large grain size crystal layer having the high coercive force is used as the perpendicular magnetization layer.

The experimental results of measuring the coercive force of the small grain size crystal layer and the large grain size crystal layer formed by the sputtering by the inventor will be described in detail below. Co-Cr thin film, Co-Cr-Nb
When the thin film and the Co-Cr-Ta thin film were sputtered, the sputtering conditions were set as follows (Nb
Alternatively, the spattering conditions were set equal in each case when Ta was added).

* Sputter device RF magnetron sputter device * Sputtering method Continuous sputtering. Preliminary exhaust pressure was set to 1 × 10 ^-6 Torr and then Ar gas was introduced to 1 × 10 ^-3 Torr * Base polyimide (thickness: 20 μm) * A small piece of Nb or Ta was placed on the target Co-Cr alloy. Placed composite target * Target-to-substrate distance 110mm Note that the magnetic properties of the thin film are the vibrating sample magnetometer (manufactured by Riken Denshi,
The composition of the thin film is an energy dispersive microanalyzer (KEVEX, hereinafter ED).
(Abbreviated as X) and the crystal orientation was measured by an X-ray diffractometer (manufactured by Rigaku Denki).

Addition of Nb as a third element to Co-Cr (2-10 at%
The same phenomenon occurs in the addition range), and a hysteresis curve in the in-plane direction when a 15 KOe magnetic field is applied to a recording medium obtained by sputtering a polyimide base with a film thickness of 0.2 μm is shown in FIG. From the figure, it can be seen that the hysteresis curve abruptly and irregularly rises (indicated by arrow A in the figure) in the portion where the coercive force (indicated by symbol Hc) in the in-plane direction is near zero, and so-called magnetization jump occurs. If it is assumed that the sputtered Co-Cr-Nb thin film always performs uniform crystal growth during the sputtering, the first
The magnetization jump shown in the figure should not occur, which suggests that a plurality of crystal layers having different magnetic properties are present in the Co-Cr-Nb thin film.

Then, under the same experimental conditions as shown in FIG.
FIG. 2 shows a hysteresis curve in the in-plane direction when a magnetic field of 15 KOe was applied to a recording medium obtained by sputtering r-Nb on a polyimide base with a film thickness of 0.05 μm. In this figure, it is understood that the magnetization jump of the hysteresis curve as shown in FIG. 1 does not occur, and the Co-Cr-Nb thin film at a film thickness of about 0.05 μm is a substantially uniform crystal. . In addition to this, 0.05 μm from the figure
Focusing on the coercive force Hc at a certain film thickness, 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 coercive force Hc of the initial layer that grows near the base by spattering is small, and this initial layer has been confirmed by scanning electron micrographs (see the above reference). It is considered to be a crystal layer having a diameter. Further, the layer grown above the initial layer has a coercive force Hc larger than the coercive force Hc of the initial layer, and this layer is also a large grain crystal layer confirmed by a scanning electron micrograph. Conceivable.

Co-Cr-N in which a small grain size crystal layer and a large grain size crystal layer coexist
b The reason why the magnetization jump occurs in the thin film will be described below with reference to FIGS. 3 to 5. As will be described later, the magnetizing jump is a C composition with respect to the composition ratio and the sputtering condition.
It does not occur for o-Cr-Nb thin films. When a Co-Cr-Nb thin film is formed by sputtering under predetermined conditions and a hysteresis curve of this thin film is drawn by measurement, a hysteresis curve in which a magnetization jump appears appears as shown in FIG. A hysteresis curve consisting of a small grain crystal layer can be obtained by performing spattering with a small film thickness dimension (about 0.075 μm or less, which will be described later) and measuring it (4th step).
(Shown in the figure). The large crystal grain layer is considered to have a uniform crystal structure, and the hysteresis curve shown in FIG. 3 is a combination of the hysteresis curve of the small crystal grain layer and the hysteresis curve of the large crystal grain layer. It is considered that the coercive force Hc is larger than that of the small grain crystal layer as shown in FIG.
It is considered to form a smooth hysteresis curve without a magnetization jump. That is, the presence of the magnetization jump shown in FIG. 3 indicates that two layers having different magnetic properties are formed in the same thin film, and accordingly, the first
It can be understood that the Co-Cr-Nb thin film shown in the figure also has two layers having different magnetic properties. The coercive force of the large grain crystal layer is determined by the hysteresis curve of the Co-Cr-Nb thin film in which the small grain crystal layer and the large grain crystal layer coexist. It can be obtained from the hysteresis curve obtained by subtracting the curve. From the above experimental results, it is proved that two layers having different magnetic properties are formed when the magnetization jump occurs in the hysteresis curve of the Co-Cr-Nb thin film.

The magnetic properties of each of the two layers formed during the sputtering of the Co-Cr-Nb thin film on the base are described below.
It will be described below with reference to FIG. 6 in relation to the thickness of the -Cr-Nb thin film. In FIG. 6, the film thickness dimension of the Co-Cr-Nb thin film is controlled by changing the sputtering time, and the coercive force Hc in the in-plane direction, the coercive force Hc _{⊥ in} the vertical direction, and the magnetization jump amount σj at each film thickness dimension are controlled. They are drawn respectively.

First, paying attention to the coercive force Hc in the in-plane direction,
At 0.08 μm or less, the value is extremely small (150 Oe or less), and it is considered that the magnetic permeability in the in-plane direction is high. Further, the coercive force Hc does not change significantly even if the film thickness is large. Also, paying attention to the amount of magnetization jump σj, the amount of magnetization jump is 0.075
It sharply rises at μm and draws a smooth downward convex parabola shape at a film thickness of 0.075 μm or more. Still focusing on the vertical coercive force Hc _⊥, coercive force Hc _⊥ rises rapidly with thickness dimensions 0.05 micrometers to 0.1 [mu] m, 0.1 [mu] m
The above film thickness dimension shows a high coercive force of 900 Oe or more.
From these results, the boundary between the small grain size crystal layer and the large grain size crystal layer is almost
The thickness is 0.075 μm, and the thickness is 0.0
The small grain size crystal layer of 75 μm or less is a so-called low coercive force layer with low coercive force Hc and Hc _{⊥ in the in} -plane direction and the vertical direction, and the large grain size crystal layer of 0.075 μm or more is The coercive force Hc in the in-plane direction is low, but the coercive force Hc _{⊥ in} the vertical direction is very high, which is a so-called high coercive force layer, which is a layer suitable for perpendicular magnetic recording. Furthermore, the film thickness dimension (0.0
(75 μm or less), the coercive forces Hc and Hc _⊥ in the in-plane direction and the vertical direction are low, and the coercive force Hc _⊥ in the vertical direction sharply increases at larger film thicknesses (0.075 μm or more). Even if the magnetization jump occurs due to this, it is presumed that two layers having different magnetic properties are formed in the Co-Cr-Nb thin film.

Next, Ta is added as a third element to Co-Cr (1 to 10).
The same phenomenon occurs in the range of addition of at%), and the results of the same experiment as in the case of adding Nb are shown in FIG. Figure 7 is controlled by varying the Supatsutaringu time the thickness dimensions of Co -Cr -Ta film, the coercive force Hc in the in-plane direction of each film thickness dimension, vertical coercive force Hc _⊥, the magnetization jump amount σj They are drawn respectively.
As shown in the figure, when Ta is added to Co-Cr, Co-C
Almost the same result as when Nb was added to r was obtained, and the boundary between the small grain size crystal layer and the large grain size crystal layer was at a film thickness dimension of about 0.075 μm. The small grain size crystal layer has coercive forces Hc and H in the in-plane and vertical directions.
Low c _⊥ (both Hc and Hc _⊥ 170Oe or less), so-called low coercive force layer, and thickness of 0.075μ.
m or more large crystal grain layer coercive force Hc _⊥ with respect to the vertical direction of the low coercive force Hc in the in-plane direction that is summer very high values (higher 750Oe).

It should be noted that in the above experiment, the spattering conditions and the amounts of Nb and Ta added are the above-mentioned values (Nb: 2 to 10).
At%, Ta: 1 to 10 at%), the magnetization jump does not occur, but the magnetization jump does not occur.
This means that the small grain size crystal layer and the large grain size crystal layer are also formed in the -Cr-Nb thin film and the Co-Cr-Ta thin film (see the above-mentioned reference). Magnetization jump does not occur Co-C
An example of the hysteresis curve of the r-Nb thin film is shown in FIG. FIG. 8 (A) is an in-plane direction hysteresis curve including a small grain size crystal layer and a large grain size crystal layer, and FIG. 8 (B) is an in-plane direction hysteresis curve of only the small grain size crystal layer, 8th
FIG. 6C is an in-plane hysteresis curve of only the large grain crystal layer. From each figure, the remanent magnetization Mr B in the in-plane direction of the small grain crystal layer is larger than the remanent magnetization Mr C of the large grain crystal layer, so the remanent magnetization Mr A including both crystal layers is the large grain crystal layer. Of the residual magnetization Mr C alone is more disadvantageous and the anisotropic magnetic field Hk becomes smaller. It is also known that the small grain crystal layer has a poor orientation (large Δθ50), and the coercive force Hc in the in-plane direction is also large, which is not suitable for perpendicular magnetic recording.

When the Co-Cr-Nb thin film and the Co-Cr-Ta thin film having the small grain size crystal layer and the large grain size crystal layer as described above are considered as the perpendicular magnetic recording medium, the Co-Cr-Nb thin film and the Co- If the Cr-Ta thin film is to be perpendicularly magnetized in the direction perpendicular to the film surface over the entire film thickness, the existence of the small grain size crystal layer is a very disadvantageous factor for the perpendicular magnetization (the magnetization jump is It becomes a disadvantageous factor in the case where it occurs and the case where the magnetization jump does not occur).
That is, when the magnetization jump is generated, the small grain size crystal layer has coercive forces Hc and Hc in the in-plane direction and the vertical direction.
Both _⊥ are extremely low (170 Oe or less), and it is considered that perpendicular magnetization is scarcely done in this layer. Also in the small grain crystal layer when the magnetization jump does not occur,
The coercive force Hc in the in-plane direction is larger than the coercive force Hc in the case where the magnetization jump is generated, but the coercive force Hc in the vertical direction.
_c⊥ does not have a coercive force enough to realize perpendicular magnetic recording, and it is considered that good perpendicular magnetization cannot be achieved. Therefore, even if the magnetization is performed in the direction perpendicular to the film surface, the perpendicular magnetization in the small grain crystal layer is hardly performed, and the perpendicular magnetization efficiency of the entire magnetic film is reduced. This effect is remarkable in a magnetic head such as a ring core head, which contains a large amount of in-plane components of magnetic flux. Also, paying attention to the film thickness, the Co-Cr-Nb thin film and the Co-Cr-Ta thin film can be practically used as a perpendicular magnetic recording medium (about 0.3 .mu.m).
m or less), the thickness dimension of the small grain crystal layer is 0.1 μm
Since it is almost constant below (in the experiment, when the film thickness dimension including the small grain size and large grain size crystal layers is made small, the thickness dimension of the small grain size crystal layer tends to be slightly large). The relative thickness dimension of the small grain size crystal layer with respect to the thickness dimension becomes large, and the perpendicular magnetization characteristic further deteriorates.

However, the magnetic characteristics of the small grain size crystal layer are such that the coercive force Hc in the in-plane direction is small and the magnetic permeability is relatively high, which is due to the backing layer (conventionally disposed between the Co-Cr thin film and the base). For example, Fe-Ni thin film) has similar characteristics. That is, Co-Cr-Nb thin film and Co-Cr-Ta
In a single thin magnetic film, a small grain size crystal layer having a low coercive force Hc is used as a so-called backing layer having a high magnetic permeability, and a large grain size crystal layer having a high coercive force Hc _⊥ in the vertical direction is perpendicularly magnetized. It is considered that by using it as a layer, it is possible to realize the same function in a single film structure as in a perpendicular magnetic recording medium having a double layer structure.

In view of this point, Co-Cr-Nb thin film and Co-Cr-
The change in magnetic characteristics and the difference in reproduction output when the composition ratio of the Ta thin film is changed and the thickness of each thin film is changed will be described below with reference to FIGS. 9 to 16. FIG. 9 is a diagram showing various magnetic characteristics when the composition ratio of the Co-Cr-Nb thin film is changed.
The figure shows the relationship between the recording wavelength and the reproduction output when perpendicular magnetic recording / reproduction is performed on each thin film shown in FIG.
It should be noted that the thin films shown in FIG.
As shown in FIG. 1, the No. described at the left end of FIG.
They are distinguished by attaching them to FIG. 11 and FIG. From FIG. 9, when Nb or Ta is added as a third element to Co-Cr, when the magnetization jump is generated, the coercive force Hc _{⊥ in the} vertical direction that contributes to the perpendicular magnetization has a high value, but the magnetization jump is generated. When not, the coercive force Hc _⊥ is low. Further, the perpendicular anisotropic magnetic field Hk is small when the magnetization jump is generated, and Mr / Ms is larger than that of the Co-Cr thin film. This is disadvantageous when using a ring core head having a large magnetic flux distribution in the in-plane direction. Was considered to be a condition. However, the above Co-Cr-Nb and Co-Cr Ta thin films (hereinafter Co-Cr-Nb thin films and Co-Cr-Ta thin films are collectively referred to as Co-Cr-Nb (Ta) thin films) are used as perpendicular magnetic recording media. Looking at the recording wavelength-reproduction output characteristics (shown in FIGS. 10 and 11) when used, the reproduction output of the Co-Cr-Nb (Ta) thin film in which the magnetization jump has occurred is more likely to cause the magnetization jump. Not Co-Cr-
It is better than the reproduction output of the Nb thin film and the Co-Cr thin film, and is particularly remarkable in the short wavelength region of the recording wavelength. In the short wavelength region (the recording wavelength is in the range of 0.2 μm to 1.0 μm), the reproduction output is increased even in the Co-Cr thin film and the Co-Cr-Nb thin film in which the magnetization jump is not generated. However, the Co that has a magnetic jump
The -CrNb (Ta) thin film shows a higher reproduction output increase rate than the reproduction output increase rate of each of the above-mentioned thin films, and Co-Cr-Nb (Ta) where the magnetization jump occurs.
It can be said that the thin film is particularly suitable for perpendicular magnetization at the recording wavelength. In particular, Co-Cr-Nb shown in Nos. III and IV
As shown in FIG. 9, in the thin film, the saturation magnetization Ms was obtained for the thin films shown in No. V and VI in which no magnetization jump was generated.
Is as low as 100 emu / cc or more, the output characteristics are good in the short wavelength region. In the above short wavelength region, the reproduction output curve has a parabolic shape that is convex upward, but Co-Cr-N in which the magnetization jump is generated in the entire region.
The b thin film was able to obtain a larger reproduction output than the Co-Cr thin film and the Co-Cr-Nb thin film in which no magnetization jump occurred.

As described above, it is considered that the improvement of the output characteristics in the short wavelength region is caused by the occurrence of the magnetization jump. The coercive force Hc in the in-plane direction of the small grain crystal layer formed in the magnetic layer having the magnetization jump is smaller than the coercive force Hc of the small grain crystal layer formed in the magnetic layer having no magnetization jump. Is.

Here, the ratio of the coercive force Hc in the in-plane direction of the small grain crystal layer to the vertical coercive force Hc _⊥ of the large grain crystal layer. (Hereafter this ratio Is called the coercive force ratio). As shown in FIG. 9, a thin film having a magnetic layer in which a magnetization jump is generated has a coercive force ratio. The value of is less than 1/5. However, in a thin film having a magnetic layer with no magnetic jump, the coercive force ratio The value of is as large as about 1 / 1.6. According to the experiment by the present inventor, the coercive force ratio at which the magnetization jump occurs It seems that the upper limit value of is about 1/5. Generally, the perpendicular coercive force Hc _⊥ of the perpendicular magnetic layer suitable for performing perpendicular magnetic recording and reproduction is up to about 1500 Oe, and the small grain crystal layer in which the magnetization jump occurs is appropriately used as a so-called backing layer. In-plane coercive force Hc
Is considered to be about 30 Oe on average, so the coercive force ratio It seems that the lower limit value of is around 1/50. That is, when forming the magnetic layer, the coercive force ratio The value of By selecting such a value, it is possible to realize a perpendicular magnetic recording medium in which a magnetization jump occurs, and thus a reproduction output is particularly good in a short wavelength region. Coercive force ratio The value of can be adjusted by changing the composition ratio of the magnetic material and by appropriately selecting spattering conditions.

Next, the reason why the reproduction output is improved in the magnetic layer in which the magnetization jump is generated will be described below.

The Co-Cr-Nb (Ta) thin film has a small grain size crystal layer 2 having a low coercive force in the vicinity of the base 1 and a high coercive force particularly in the vertical direction above the base layer 1 as shown in FIG. 12 when the magnetic layer is formed by sputtering. Forming a two-layer structure with a large grain crystal layer 3 having The value of Therefore, the magnetic layer formed by the layers 2 and 3 is a magnetic layer in which a magnetic jump is generated. Therefore, the magnetic flux lines emitted from the magnetic head 4 reach the small grain size crystal layer 2 through the large grain size crystal layer 3, and within the small grain size crystal layer 2 having low coercive force and high magnetic permeability. It is considered that the magnetic flux travels in the in-plane direction and is abruptly absorbed by the magnetic pole portion of the magnetic head 4 so that the large grain crystal layer 3 is perpendicularly magnetized. Therefore, the magnetic loop formed by the magnetic flux has a horseshoe shape as shown by an arrow in FIG. 12, and the magnetic flux sharply penetrates through the large grain crystal layer 3 at a predetermined perpendicular recording position. A large perpendicular magnetization is performed.
Here, focusing on the coercive force Hc in the in-plane direction of the small grain crystal layer 2 with and without the magnetization jump, the in-plane with the magnetization jump as shown in FIG. 9 is obtained. The coercive force Hc in the direction is smaller than the coercive force Hc when the magnetization jump is not generated. As is well known, in order for the small grain size crystal layer 2 to function as a so-called backing layer, it is desirable that it has a resistance magnetic force and a high magnetic permeability, and thus Co-C in which a magnetization jump occurs.
It is presumed that the r-Nb (Ta) thin film has a better reproduction output. The small grain size crystal layer 2 has a coercive force H
Since c is not completely zero and has a predetermined coercive force, the magnetization corresponding to this coercive force can be performed.
When perpendicular magnetic recording is performed, the large grain crystal layer 3 has a 14th
As shown in the figure, a plurality of magnets corresponding to a predetermined bit interval and having opposite magnetization directions are alternately formed. Then, to the small grain size crystal layers 2 at the lower ends of the formed magnets, the magnetic flux (the 14th
(Indicated by an arrow in the figure) is formed and this is magnetized. As a result, the demagnetizing action of each adjacent magnet is eliminated, and this phenomenon is particularly noticeable in perpendicular magnetic recording where the density of each adjacent magnet is high, that is, the recording wavelength is small, so increase the reproduction output in the short wavelength region. You can Further Co
Focusing on the film thickness dimension of the -Cr-Nb (Ta) thin film, increasing the film thickness dimension means increasing the thickness dimension of the large grain crystal layer 3 (the small grain crystal layer 2). (The thickness dimension is substantially constant.) By increasing this, the distance between the magnetic head 4 and the small grain crystal layer 2 becomes large, and the effect of absorbing the magnetic flux by the small grain crystal layer 2 is slight, and FIG. The magnetic force lines emitted from the magnetic head 4 as shown by the arrows cross the large grain crystal layer 3 without reaching the small grain crystal layer 2 and are drawn into the magnetic poles of the magnetic head 4. Therefore, the magnetization in the perpendicular direction becomes dispersed and weak, and good perpendicular magnetization cannot be performed. However, if the film thickness of the Co-Cr-Nb (Ta) 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 absorbing the magnetic flux by the small grain crystal layer 2 becomes large, and The magnetic flux emitted from the head 4 surely advances to the small grain crystal layer 2 to form the horseshoe-shaped magnetic loop. That is, since the magnetic flux that contributes to the perpendicular magnetization is a horseshoe-shaped extremely sharp magnetic field, it is considered that the residual magnetization becomes large and good perpendicular magnetization is performed. That is, the smaller the thickness of the Co-Cr-Nb (Ta) thin film is (the thinner the recording medium is), the better the perpendicular magnetization can be performed. It is possible to realize a thin recording medium having a good hit (according to the experiments of the present inventor, high output can be maintained up to a thickness of about 0.1 μm to 0.3 μm). In addition to this, Co-Cr-Nb (Ta which forms a layer having a high coercive force and a layer having a low coercive force as described above
) Since the thin film is formed by continuous sputtering,
It is unnecessary to change the spattering conditions or change the target in order to form a two-layer structure.
The step of forming a -Cr-Nb (Ta) thin film can be facilitated, the sputtering time can be shortened, and the perpendicular magnetic recording medium can be manufactured at low cost and with mass productivity. Further coercive force ratio The value of The coercive force H in the in-plane direction of the small grain crystal layer 2 is selected as
Since c is not an extremely small value with respect to the coercive force Hc _⊥ of the large-grain-diameter crystal layer 3, good perpendicular magnetic recording / reproduction can be performed without generating shocking Barkhausen noise.

As described above, according to the perpendicular magnetic recording medium of the present invention, in the perpendicular magnetic recording medium having the magnetic layer formed by the upper layer and the lower layer, the coercive force of the upper layer in the vertical direction is Hc _⊥ ,
When the coercive force in the in-plane direction of the lower layer is Hc, The value of By selecting so that the magnetic layer of the perpendicular magnetic recording medium becomes a magnetic layer having a magnetization jump, the magnetic flux emitted from the magnetic head easily enters the lower layer having a low coercive force and then advances in the horizontal direction, and then the magnetic head. Since the magnetic pole of the magnetic field rapidly penetrates the upper layer having a high coercive force and is absorbed by the magnetic pole of the magnetic head, perpendicular magnetic recording and reproduction capable of achieving high reproduction output can be performed due to strong residual magnetization in the upper layer. In addition to this, especially when the recording wavelength is short, particularly excellent perpendicular magnetization is performed and a good reproduction output can be obtained, and the lower layer has a magnetization jump, that is, the coercive force in the in-plane direction is small, and Since it is a layer with high magnetic permeability, it reliably functions as a so-called backing layer and its coercive force is not extremely small compared to the coercive force of the upper layer, so it has impact resistance. The Barkhausen noise perform good perpendicular magnetic recording reproducing without occur has the features of equal if possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a hysteresis curve of a Co--Cr--Nb thin film which is a magnetic film of one 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, 3 to 5 are views for explaining the reason why the magnetization jump occurs, and FIG. 6 is a view showing that the Co-Cr-Nb thin film has a two-layer structure and the magnetic characteristics of each layer,
FIG. 7 is a diagram showing that the Co-Cr-Ta thin film has a two-layer structure and the magnetic characteristics of each layer, and FIG. 8 is an example of the hysteresis curve of the Co-Cr-Nb thin film in which no magnetization jump occurs. And FIG. 9 show various magnetic characteristics of the Co-Cr-Nb thin film and the Co-Cr-Ta thin film in which the magnetization jump is generated, and Co in which the magnetization jump is not generated.
-Compared with the magnetic characteristics of the -Cr-Nb thin film and the Co-Cr thin film, FIGS. 10 and 11 show the recording wavelength when perpendicular magnetic recording and reproduction were performed on each thin film shown in FIG. FIG. 12 is a diagram showing a relationship of reproduction output, FIG. 12 is a diagram showing a magnetic loop formed by magnetic flux when the thickness dimension of the recording medium of the present invention is small, and FIG. 13 is a thickness dimension of the recording medium of the present invention being large. FIG. 14 is a diagram showing a magnetic loop formed by a magnetic flux in the above case, and FIG. 14 illustrates the magnetic flux that communicates between the lower end portions of a plurality of magnets formed in the small grain size crystal layer and magnetized in the large grain size crystal layer. FIG. 1 ... Base, 2 ... Small grain crystal layer, 3 ... Large grain crystal layer, 4 ... Magnetic head.

Front Page Continuation (72) Inventor Eiichiro Imaoka 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa Japan Victor Company of Japan (56) References JP-A-60-21507 (JP, A) JP-A-59- 98321 (JP, A) JP-A-60-101710 (JP, A)

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium having a magnetic layer formed of an upper layer and a lower layer, wherein the coercive force of the upper layer in the vertical direction is Hc _⊥ and the coercive force of the lower layer in the in-plane direction is Hc.
Then, the ratio The value of A perpendicular magnetic recording medium characterized by being selected as follows.