JPH01185816A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase output without increasing coercive force by specifying ratio between an area of the part enclosed by a straight line extending a magnetization saturation region, a demagnetization curve and a tangent near the coercive force of the demagnetization curve and the area of the part enclosed by a hysteresis loop. CONSTITUTION:The area of the part 4 enclosed by the straight line extending the magnetization saturation region, the demagnetization curve 11 and the tangent 3 near the coercive force of the demagnetization curve is designated as S1 and the area of the part 5 enclosed by the hysteresis loop 1 is designated as S2. The value of S1/S2 is set at about <=0.03. The hysteresis loop 1 in the direction perpendicular to the film plane is inclined overall by the diamagnetic field thereof but a head approaches the medium at the time of recording and reproducing of actual signals and, therefore, the diamagnetic field decreases and the hysteresis loop rises. The recorded magnetization (residual magnetization) increases if the value of S1/S2 is about <=0.03. The large output is thereby taken without increasing the coercive force.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a perpendicular magnetic recording medium, which is a type of magnetic recording medium. [Prior Art] A perpendicular magnetic recording system has been proposed as a high-density recording system, and much research has been conducted thereon. In particular, a great deal of effort has been put into increasing the signal reproduction output. Conventionally, for this purpose, the coercive force of the perpendicular recording layer has been increased. (Furuya et al. “Recording and reproducing process of perpendicular recording media” Journal of the Japan Society of Applied Magnetics vol. 1.8. No. 2
．． 1984). There are various possible reasons why the output increases due to the increase in coercive force, but qualitatively, the following factors are considered to be one of them. To explain this, when a head (for example, a single-pole head) approaches a saturated recording medium for reproduction, the demagnetizing field in the direction perpendicular to the film surface of the perpendicular recording layer of the medium is reduced. Here, the demagnetizing field is a magnetic field that depends on the geometrical shape and magnitude of magnetization in a magnetic material; conceptually, the longer the length in the direction of magnetization, the smaller it is, and the shorter it is, the larger it is. Therefore, when the magnetization is oriented in a direction perpendicular to the film surface as in a perpendicular recording layer, the largest demagnetizing field is generated compared to when the magnetization is oriented in other directions. When the head, which is a magnetic material, approaches such a place, the geometrical shape around the magnetization changes, and the demagnetizing field is reduced. Now, the magnetization felt by the head in this state corresponds to the residual magnetization Mr in FIG. However, Figure 2 shows the major loop (a loop in which the magnetization is saturated by -1) of the dish curve (relationship between magnetization and applied magnetic field) of the perpendicular recording layer in the direction perpendicular to the film surface when the head is close. , other conditions of the perpendicular recording layer of the medium, for example, if the saturation magnetization Ms is made equal and the coercive force is increased to Hc', the residual magnetization becomes Mr', and M
r'> Mr. Therefore, in this case, the magnetization felt by the head is greater for the medium with a higher Hc, and the reproduction output increases accordingly. However, a medium with high retention strength has poor recording efficiency, resulting in, for example, deterioration of overwrite characteristics (a characteristic in which new data is written on top of old data without first erasing it, thereby erasing old data). This is because when the coercive force of the medium is large, the recording magnetic field from the head is insufficient to overcome the coercive force in the direction perpendicular to the film surface of the perpendicular recording layer and form recorded magnetization.

[Alternating current] This is caused by the fact that even though it is possible to write to a certain extent on a medium in an erased state, a sufficient magnetic field cannot be generated to rewrite the recorded magnetization on a medium in a recorded state. To explain this with a drawing, the dotted line in FIG. 3 is the MH convex curve major loop of the perpendicular recording layer in the direction perpendicular to the film surface when the head is close. When magnetizing a medium that has been erased by AC as shown in Figure 3(a), the magnetization is indicated by the origin O, and once the recording magnetic field of the head is generated positively and then the recording magnetic field is removed, the state of magnetization is It changes as shown by the arrow, and the magnetization has the magnitude shown at point A. On the other hand, as shown in figure (b), even if the recording magnetic field of the head is made positive in order to rewrite the medium that initially has negative magnetization B to positive, the one magnetization N that remains after the magnetic field is removed is B. Since the signs are the same, it was desired to increase the output without increasing the coercive force by rewriting the code C. This invention was made to solve the above-mentioned problems, and it is possible to obtain a large output without increasing the coercive force. ! The perpendicular magnetic recording medium according to the present invention which provides a magnetic recording medium has a hysteresis loop (1) in the direction perpendicular to the film plane at least in the vicinity of the surface of the perpendicular magnetic recording layer, in which a straight line (wato, The area of the part (4) surrounded by the demagnetization curve 0 and the tangent line (3) near the coercive force of the demagnetization curve is 81, and the hysteresis loop (
Assuming that the area of the part (5) surrounded by 13 is 82, s+,
, 's* is about 0.0] or less. [Operation] In this invention, the hysteresis loop (υ) in the direction perpendicular to the film surface is tilted overall due to the demagnetizing field, but since the head approaches during actual signal recording and reproduction, the demagnetizing field is When the value of S, /S, is about 0.0 or less, the recorded magnetization (residual magnetization) becomes large.Examples of the Invention] Below, An embodiment of this invention will be explained with reference to the figures.
In the figure, (υ is the hysteresis loop in the direction perpendicular to the film surface of vertical @ magnetic recording 17), (2) is the straight line extending the magnetization saturation region, σ is the demagnetization curve, and (3) is the coercive force of the demagnetization curve. The tangent line in the vicinity (4) is the straight line extending the magnetization saturation region (
21, the demagnetization curve αυ, the part surrounded by the tangent of the demagnetization curve near the coercive force, and (5) is the hysteresis loop (the part surrounded by υ).First, when the head records a signal on the medium, When the head is close to the head, the demagnetizing field in the direction perpendicular to the media surface is reduced and the slope of the hysteresis loop becomes smaller.This situation is shown in Figure 2.In this state, the coercive force By applying a sufficiently large recording magnetic field, the perpendicular magnetization of the medium is saturated.As the head and medium move relative to each other, the demagnetizing field returns, and when the recording magnetic field decreases, the recorded magnetization remains as shown in Figure 1. It is expressed as magnetization (8).Next, during reproduction, the demagnetizing field is reduced by the proximity of the head, resulting in a hysteresis loop as shown in Figure 2, and the recorded magnetization is expressed as residual magnetization (8), and this large The output that is approximately proportional to the second
It is desirable to increase the value of residual magnetization (81) in the figure. In conventional longitudinal recording media, unlike perpendicular magnetic recording media, the demagnetizing field can be ignored, so the shape of the hysteresis loop changes due to the approach or separation of the head, etc. can be ignored, and the ratio of (residual magnetization)/(saturation magnetization) is called the squareness ratio. (If this ratio is close to 1, the output can be large.)However, in the present invention, (4) is. 5) The SsD ratio S, /S is not simply a re-expression of this conventional squareness ratio.The conventional squareness ratio is a characteristic characteristic of the medium that takes a nearly constant value regardless of the position of the head. When this is used as an indicator of the perpendicular magnetic recording layer, its value varies greatly depending on the position of the head with respect to the part of the medium that is currently being focused on.This is shown in Figure 1 and @ It is clear from comparing Figure 2. In other words, it is not a value unique to the medium.Moreover, even when the head is in its operating state, when it is closest to the part of the medium that is of interest, the demagnetizing field is not negligible; Then, the magnitude of the demagnetizing field will vary depending on the usage conditions of the head (spacing, etc.), and the squareness ratio will therefore take a different value.Also, the curve when the head is close cannot be easily measured.10,000, S1/ The value of S is the value of medium adhesion, and the basis for this is that the MH curve can be easily measured and can express the degree of residual formation under actual usage conditions.
This is an indicator of perpendicular magnetic recording media. Various means can be considered to realize the present invention by suppressing the value of S1/S to about 0.03 or less, and for example, it can be realized as follows. In FIG. 4, a soft magnetic material containing Fe and Ni as main components is provided on an aluminum alloy whose surface has been anodized by a known sputtering method. For example, MoC
u -FeNi (Ni content 80ωt%, Cu5ωt%
A thickness of about 0.5 μm is provided using a target of 0Mo3cB%) alloy. Furthermore, an amorphous opening is provided on this surface by sputtering. For example, target Sing and use 0.02
Provide a distance of approximately μm. Furthermore, perpendicular magnetic recording 17) is provided on this surface. For example, C
oCr (Cr content: 20 ωt%) alloy is used as a target to provide a thickness of about 0.3 μm. SL/S of the perpendicular magnetic recording layer (7) prepared in this way
The value of 2 was o, oos. In addition, in FIG. 4, CoZrNb (
A sputtered film targeting ZnlOωt%, Nb5ωt%] is provided on a soft magnetic layer. Furthermore, CoC is added to this surface.
A sputtered film targeting r (Cr 20ωt%) alloy was provided on the perpendicular magnetic recording layer (0.3 μm), and the value of S, /S, of the medium thus produced was 0.02. In FIG. 5, a soft magnetic layer mainly composed of Fe and Ni is provided by sputtering on an aluminum alloy whose surface is anodized. For example, MoCu-FeNi
(Ni content 80 (lJt%, Cu5ωt%9Mo3ω
t%] The alloy is used as a target, and a thickness of about 0.5 μm is provided. Furthermore, perpendicular magnetic recording @ (7) is provided on this surface. For example, a CoCr (Cr content: 20 ωt%) alloy is used as a target to provide a thickness of about 0.3 μm.
The value of 2 was 0.04. When the recording and reproducing characteristics of these two types of perpendicular magnetic recording media were measured using a main pole excitation type single magnetic pole head, the results shown in FIG. 6 were obtained at a recording density of 20 KFRPI. Further, since the recording/reproducing output largely depends on the coercive force as mentioned above, it is desirable that the coercive force is in the range of about 300 to about 8000 e. If the coercive force is less than 3000e, not only will the output drop significantly, but the shape of the hysteresis loop will change greatly near the origin, and S1/S may not be defined. It should be noted that recording is difficult in practice if it is 5000e or more. For example, it will look like the one shown in Figure 7. Also, if the saturation magnetization is large, the value of residual magnetization (8) in Figure 2 is also large if the value of S1/S is the same, so it is about 200 to about 700.
emu/. . It is desirable that it be at a certain level. [Effect of the invention] As described above, according to this invention, the value of s, /' s2 can be set to 0.
．． Since the value is set to about 0.03 or less, the value of residual magnetization during reproduction becomes close to the value of saturation magnetization, which has the advantage that the reproduction output becomes large.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a hysteresis loop in the direction perpendicular to the film surface to explain this invention, Fig. 2 is a hysteresis loop in which the reciprocal field is reduced due to the proximity of the heads, and Fig. 3 is a diagram showing the state of overwriting. FIG. 4 is a sectional view of a perpendicular magnetic recording medium showing an embodiment of the present invention, and FIG. 5 is a sectional view of a conventional perpendicular magnetic recording medium. (1) Hysteresis loop in the direction perpendicular to the film surface, (2
)... Straight line extending the magnetization saturation region, (3)... Tangent line near the coercive force of the demagnetization curve, (6)... Substrate,
關...Soft magnetic layer, 1... Amorphous layer, (7)... Perpendicular magnetic recording layer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] In the hysteresis loop (1) in the direction perpendicular to the film surface of the perpendicular magnetic recording layer (7) provided on the substrate (6), the straight line (2) extending the magnetization saturation region, the demagnetization curve (11), and the demagnetization The area of the part (4) surrounded by the tangent line (3) near the coercive force of the curve is S_1, and the area of the part (5) surrounded by the hysteresis loop (1) is S_2, and S_1/S
A perpendicular magnetic recording medium characterized in that the value of _2 is about 0.03 or less.