JPS63247914A - Flexible disk - Google Patents

Abstract

PURPOSE:To obtain a soft magnetic layer having small intra-surface magnetic anisotropy by forming the low-coercive force soft magnetic layer on a flexible substrate in such a manner that the torque curve measured within the film plane can be approximated by the specific equation. CONSTITUTION:The flexible disk is formed with the soft magnetic layer S having the low coercive force of <=10 oersted and and a perpendicular magnetic recording layer R on the flexible substrate F. The layer S of this disk is so formed that the torque curve measured within the film plane by a torque magnetometer can be approximated by the equation I and that the absolute value of Ku in this equation is <=1.5X10<3>erg/cc. In the equation, L is the torque acting on the layer S per unit volume thereof; Ku is a magnetic anisotropic constant; thetais the angle between the axis of easy magnetization within the film plane of the layer S and the measuring magnetic field of the torque magnetometer. The easy mass production of the film S having the small intra-surface magnetic anisotropy with good controllability is thereby permitted.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is based on a nonmagnetic flexible substrate such as a polyethylene terephthalate (PET) film, a soft magnetic layer such as a NiFe alloy film, and a perpendicular magnetic layer such as a CoCr alloy film. The present invention relates to a flexible disk for perpendicular magnetic recording having a two-layer M4 structure in which recording layers are sequentially laminated.

[Prior Art] In place of the conventional coating-type magnetic recording medium having a recording layer in which fine ferromagnetic powder is dispersed in a binder resin, in recent years, with the demand for high-density recording, media of the perpendicular 1'I magnetic recording system have been developed. It is being actively researched, and is expected to be applied particularly to floppy disks, with the above-mentioned two-layer perpendicular magnetic recording medium attracting attention. (Special Publication No. 58-91 No. 1
Nikkei Electronics October 25, 1982 issue p.
141 etc.) The basic configuration of the above-mentioned perpendicular magnetic recording medium is as follows:
As is known from Japanese Patent Publication No. 58-91, etc., it is made of a Ni-Fe alloy film or the like with a thickness of about 0.2 to 1.0 μm, which acts as a magnetic flux concentration layer and is created by sputtering or other means on a supporting substrate. 0, 1 to 0, which acts as a soft magnetic layer and a recording layer.
High sensitivity due to the sequential lamination of perpendicular magnetic recording layers made of C0Cr alloy films with a thickness of approximately 7 μm.

High-density recording is possible.

By the way, with the above-mentioned two-layer perpendicular magnetic recording medium, there was no problem with floppy disks made by rotating the support substrate, but it was not a problem when the film was made for industrial production and was made in a donut shape while being continuously run. On removed floppy disks, the playback output may change within one cycle within the same track, and it is known that this is based on the in-plane magnetic anisotropy of the soft magnetic layer, and a solution to this problem is desired. ing.

In contrast, “I E E E T transact
ion on MaaneticsJ vol, Mao
-20, k5 (1984), pp. 782-784, describes changes in reproduction output caused by such magnetic anisotropy (
Modulation) and a method of isotropy by balancing the oblique incidence effect of sputtered particles and the magnetic field-induced anisotropy effect to eliminate magnetic anisotropy are described.

However, the above conventional method was obtained based on experimental results using an in-line batch sputtering system, and is difficult to apply to continuous film formation for mass production.

That is, the magnetic anisotropy of soft magnetic films during mass production remains unresolved, and a reliable method for resolving this problem has been awaited.

[Object of the present invention] The present invention is directed to a two-layer film having a soft magnetic layer and a recording layer. Periodic fluctuations in playback output (modulation: JIS C629
We propose a small flexible disk (see 0).

[Structure and effects of the present invention] In view of the above-mentioned current situation, the present inventors have developed a method using a continuous sputtering method.
As a result of intensive studies focusing on the factors that cause magnetic anisotropy in soft magnetic films such as permalloy (Ni-Fe alloy) films formed on organic polymer film supports with a thickness of about 0 μm, we found that
A soft magnetic film is used as a support film or a perpendicular magnetic recording layer (CoC
We succeeded in determining the inverse magnetostrictive effect caused by the stress exerted by the r-alloy film, etc.), thereby completing the present invention.

That is, the present invention provides a flexible disk in which a soft magnetic layer with a low coercive force of 1000 (oersteds) or less and a perpendicular magnetic recording layer are formed on a flexible substrate, the soft magnetic layer comprising:
The torque curve measured in the film plane by a torque magnetometer is L
--Ku ・sin 2θ (where, L is the torque acting per unit volume of the soft magnetic film, KU is the magnetic anisotropy constant,
θ can be approximated by the equation (the angle between the axis of easy magnetization in the film plane of the soft magnetic film and the measurement magnetic field of the torque magnetometer), and Ku in this equation
It is characterized in that the absolute value of is 1.5x103erg/cc or less.

In the present invention, the soft magnetic layer has magnetic anisotropy based on the reverse magnetostriction effect due to the stress that the soft magnetic layer receives from other layers, thereby canceling out the magnetic anisotropy caused by other causes of magnetic anisotropy. Preferably, it is approximately isotropic.

More preferably, the magnetic anisotropy generated by the inverse magnetostriction effect in the soft magnetic layer is approximately uniaxial magnetic anisotropy, and the absolute value of the magnetic anisotropy constant is greater than 2 x 102 ero/cc 3 x 103 era/cc. It is a flexible disk with a smaller size. In particular, the soft magnetic film is parallel to the film surface of the magnetic field strength of the part where the sputtered particles are deposited on the flexible substrate, which is continuously moved along a rotating can by a continuous sputtering device having a facing target cathode or a magnetron sputtering cathode. It is preferable to use a flexible disk that is a permalloy film formed under conditions such that the component is at least 5 Gauss at least once.

The present invention will be explained in detail below.

FIG. 1 shows the configuration of a preferred flexible disk for perpendicular magnetic recording of the present invention. In the figure, F is a support material, and for applications such as floppy disks, still electronic cameras, and image files, organic materials with a thickness of about 30 μm to 120 μm such as polyethylene terephthalate, polyethylene-2,6-naphthalene dicarpoxylate, and polyimide are used. A polymer film is preferably used.

S in the figure is a soft magnetic layer which is a feature of the present invention, and a layer having a coercive force (Hc) of about '10 Oe or less and a thickness of about 0.2 .mu.TrL to 0.7 .mu.m is usually used. Various materials can be used, and C0
Examples include a Zr-based amorphous alloy film and a Ni1''e-based alloy (permalloy) film.Especially, raw material costs are low;
Permalloy is preferred because the material is easily available and has appropriate magnetic properties. There are various types of permalloy such as not only Ni Fe alloy but also MO permalloy, cut MO permalloy, corrosion resistant permalloy, high hardness permalloy, and any of them can be applied.

R in the figure is a perpendicular magnetic recording layer, and a CO and Cr alloy film having a saturation magnetization (MS) of about 200 to 900 en+u/cc is preferably used. In addition, there are roughly a few in CO and Cr.
t% of a third element such as Re, W, MO, Ta, etc., CoV alloy film, FeCr alloy film, and even co
-coO vapor deposited film may be used. The key is a thickness of 061μ with moderate Ms, Hc of several hundred oe, and perpendicular magnetic anisotropy.
A membrane of about 0.5 μm to 0.5 μm is used.

P in the figure is a protective layer provided as necessary for the purpose of durability and the like. For example 3i 0 to ensure durability
2. Thickness of hard carbon, SiN, etc. 0.01 μm ~
A thin film of about 0.03 μm is provided between each layer F, S, R, P, and other intermediate layers.

It may have a base layer, an adhesive layer, etc. Furthermore, in a flexible disk, each layer having the same structure as shown in FIG. 1 is normally formed on both sides of the support F, but it goes without saying that it is sufficient to form each layer on only one side.

Vacuum evaporation, sputtering, ion blating, plating, etc. have been considered for the production of each of the above layers, but sputtering is preferred because it has good magnetic properties, pus strength, and film adhesion strength, and it is easy to control the alloy composition. Applies to the present invention.

In particular, the magnetron sputtering method, which has a long film running system that is excellent in mass production, or the facing target sputtering method are preferably applied. In general, the facing target sputtering method is most preferable for sputtering an alloy target with a large saturation magnetization (Ms) and high magnetic permeability, such as a permanent carp.

A winding-type opposed target sputtering apparatus used in an embodiment of the present invention will be explained below with reference to FIG. FIG. 2 shows a sputtering apparatus based on the facing target sputtering method known from Japanese Patent Application Laid-Open No. 57-158380. In the figure, I: is a film serving as a substrate, 1 is a supply roll, 2.
3 is a guide roll, 4 is a winding roll, 5 is a can whose temperature can be controlled, 6 is a mask, 13 is a partition plate for differential exhaust, P is a facing target cathode with two targets 11 facing each other, 12 is a target Permanent magnet on the back
B is a magnetic field between targets, S is a cover that shields particle scattering, 20 is a vacuum chamber, 21 is a gas introduction system such as argon, 2
2 is an exhaust system. Note that the vacuum pump, the target cooling water system, and the power source for supplying power to the target are the same as those known in the art and are not shown.

As is clear from the above structure, its basic structure is the same as that of the facing target sputtering apparatus disclosed in the above-mentioned Japanese Patent Application Laid-open No. 57-158380, and its operation is well known, so a description thereof will be omitted.

Then, a perpendicular magnetic recording medium is obtained in the following manner. That is, a long flexible substrate such as a polymeric resin film is used as the substrate, and the rolled body is loaded onto the supply roll 1 as shown in the figure, and the film F fed out from the wound body is The target 11 of the cathode P is made of a permalloy alloy, and the target 11 of the cathode P is made of a permalloy alloy. is sputtered to continuously form a permalloy film on a long film. Next, change the target 11 to coOr alloy,
A CoCr alloy film is formed on the permalloy crotch by a similar operation. Furthermore, if necessary, a permalloy film and a CoCr
By forming an alloy film and further forming protective layers on both surfaces if necessary, a perpendicular magnetic recording medium having the structure illustrated in FIG. 1 is obtained.

A flexible disk can be obtained by punching the long medium produced in this way into a disk shape, but as mentioned above, the soft magnetic film continuously formed on the long film F has a high coercive force. It has been found that when the magnetic field is small (approximately 10 Qe or less), it tends to have magnetic anisotropy, and that flexible disks with bendable soft magnetic films have the disadvantage of large output fluctuations while the magnetic herad goes around the disk. .

The soft magnetic film, which is a feature of the present invention, will be explained below.

Although the soft magnetic film (permalloy film) formed as in the above example may have some anisotropic dispersion, it was found that it generally substantially exhibits uniaxial magnetic anisotropy.

FIG. 3 shows an example of a torque curve of a permalloy film measured using a torque magnetometer in a magnetic field sufficient to saturate magnetization. In the example shown in Figure 3, the magnetic anisotropy constant (Ku) of the permalloy film determined from the maximum torque is 1,9x103
erg/CC, and in a flexible disk with a C0Cr film formed on the permalloy crotch, which has such a large anisotropy, the modulation of the playback output is JIS -
This is greater than the 10% stipulated in C-6290.

As a result of various studies, in order to obtain a modulation of 10% or less, for a soft magnetic film exhibiting approximately -axial magnetic anisotropy, the torque curve is approximated by L--Ku ・sin 2θ, and Kll in this equation is Absolute value is 1.5X103erg
It was found that it is necessary to be less than /cc.

By the way, the reason for the development of magnetic anisotropy in a soft magnetic film continuously sputtered on a flexible film running along the can (5 in Figure 2) as described above has not been clearly explained. For reasons unknown, it has been difficult to obtain soft magnetic films with small magnetic anisotropy. In order to reduce the magnetic anisotropy of a soft magnetic film, the idea is to eliminate all possible causes of anisotropy.
In order to make the magnetic field parallel to the upper board surface (B in Figure 2) zero, measures such as placing a permanent canceling magnet on the inside of the back of the can have been proposed, but this has not been successful in practice. Apparently not. In particular, in the facing target sputtering method, the magnetic field distribution between both nuggets is deeply involved in the sputter discharge characteristics, so it is impossible to place a permanent magnet near the facing target space that would disturb the magnetic field distribution. , the above conventional means cannot be applied.

Based on this background, as a result of various studies, the present inventors determined that the magnetic anisotropy of a soft magnetic film continuously deposited by sputtering can be determined by the inverse magnetostrictive effect induced by the stress that the soft magnetic film receives from the substrate film. It has been found that by controlling the following, a permalloy film having a uniaxial magnetic anisotropy constant (Ku) less than the target value can be obtained with good reproducibility.

The inverse magnetostriction effect will be explained below based on an experimental example (comparative example).

Figure 4 (ω is 0, 30 m thick MO bar voi film (Ni 81 wt%, Ni 81 wt%,
The running method of the original long film (Fe 14 wt%, MO 5 wt%) in the longitudinal direction: MD: solid line in Figure 4) and width direction (direction perpendicular to MD: TD: dotted line in Figure 4) is 50 HzM. -Magnetization curve measured with H-loop tracer (
The horizontal axis is the measured magnetic field H, and the full scale is ±20 0e
), and the fourth presentation is the magnetization curve (±2° Oe full scale) of the MO permalloy crotch obtained by removing the PET film with an organic solvent and taking it out as a single piece.

On the other hand, the magnetostriction constant (λ) of the MO permalloy film is determined by
It was measured by the method described in Section I. That is, the M-8 curve is measured with a predetermined tension t applied to the Mo permalloy film in a predetermined direction, for example in the MD direction, and as is well known, a tangent line is drawn from the origin to the magnetization curve to find the line of saturation magnetization MS. Find the intersection point with the magnetic field indicated by the intersection point, that is, the anisotropic magnetic field H
Measure k.

Then, the anisotropic magnetic field 1-1 k for various tensions was measured by changing the tension t, and from the gradient, H per unit tension was calculated.
Find Δ1-1k while k changes. Also, using the Young's modulus of the film and the MO permalloy layer, the stress σ' acting on the MO permalloy layer when unit tension is applied is calculated according to the formula of mechanics of materials. Then, obtain the magnetostriction constant λ using the following method.

λ-(Ms/3)X(ΔHk/a') Here, the unit is saturation magnetization MS is [Wb#].

The stress σ' is [N/m・*gf], and the change in the magnetic field Δ
l) k is [A/m-Kgf].

The magnetostriction constant λ of the Mo permalloy film was determined by the above measurement method.
was found to be −1,5×10″6.

From the comparison between Figure 4 (ω and +to), it is clear that the Mo permalloy film is under compressive stress from the MD force direction substrate film, and the magnitude of that stress is shown in Figure 4 (Figure 4 and (b)).
The change (ΔHk) of the anisotropic magnetic field (Hk) obtained from the inclination of the hard magnetization axis is expressed by the formula: σ−−ΔHk・MS / (3
・λ) (However, σ is the stress that the soft magnetic film receives from the substrate film, and 1yls is the saturation magnetization of the soft magnetic film.), and is obtained by substituting 9.7x 1G" dyn
/cd. In other words, the anisotropy constant (Ka) induced by the inverse magnetostriction effect is expressed as σ=-(3/2)・λ・σ
In this experimental example, Ka-2,2
x103 era/cc (direction of action with MD force direction as axis of easy magnetization). As can be understood from the above equation, the value of σ in the anisotropy constant and the direction of the easy axis can be changed by the respective values and signs of the magnetostriction constant λ and stress σ, and the approximately -axial magnetic anisotropy can be changed. The magnetic anisotropy of the soft magnetic film is expressed as the sum of magnetic anisotropy constants due to various causes, so that the magnetic anisotropy of the soft magnetic film can be controlled by controlling Ka.

And MO permalloy g! obtained in the above experimental example (comparative example)! (The composition and magnetostriction constant are described above.) The magnetic anisotropy of M
It is considered that this is the sum of the magnetic anisotropy effect, which makes the D easy axis in the force direction, and the inverse magnetostrictive effect, which makes the same <MD easy axis in the force direction. In other words, both magnetic anisotropy effects act in the same direction, resulting in large magnetic anisotropy.

From the above, it has been found that in order to reduce the magnetic anisotropy of a soft magnetic film, the inverse magnetostriction effect and the effects due to other causes of magnetic anisotropy should be made to cancel each other out. In the facing target sputtering method, if the relative arrangement between the can 5 and the facing target cathode P in Fig. 2 is rotated by 90 degrees, the magnetic field on the substrate film will be in the TD direction, causing an action with the TD direction as the easy axis. Although this is possible as a model, such an arrangement is not suitable for mass production because the effective period of the film is regulated by the distance between both targets. Therefore, even in the facing target sputtering method, it is preferable to actively utilize the inverse magnetostriction effect rather than the magnetic field-induced anisotropy effect that occurs according to the magnetic field direction.

The present invention deals with the case where magnetic anisotropy is expressed due to the directional arrangement of atomic pairs found in NiFe alloys, etc. It is preferably applied in situations where directional effects are unavoidable.

In this case, if the magnetic field strength is 5 Gauss or more, the induced anisotropy effect in the magnetic field cannot be ignored, but if it is 5 Gauss or less, the effect is small and the effect of the present invention is also small.

Therefore, when forming a film while transporting the substrate, it is preferable to form the film under conditions in which the magnetic field parallel to the substrate surface is 5 Gauss or more at least once during film formation.

The absolute value of the anisotropy constant (Ka) expressed by the above-mentioned inverse magnetostriction effect is 3 × 10 at 2 × 1102er/cc or more.
3 er (1/cc or less is desirable. 2 X 1102
When it is less than er/cc, it is insufficient to cancel other anisotropic effects, and when it is more than 3 x 10' erQ/cc, anisotropy becomes dominant due to the inverse magnetostriction effect, resulting in soft The magnetic anisotropy of the magnetic film often becomes large.

In addition, in the above experimental example (comparative example), the stress σ that the Mo permalloy film receives from the substrate film is 9.7 × 108 dyn.
/crA. In order to effectively utilize the inverse magnetostrictive effect, the stress must be uniaxial and have an appropriate value, preferably approximately 5 x 10' dyn/cri or more. However, too large a stress is inconvenient because it causes curling of the medium and cracking of the film.
"dyn/cd or less is preferable. Such stress is shown in FIG. 2 as an example in a winding type continuous sputtering device, with C, substrate filter T, and F having a thickness of about 50 uTrL and a V jig rate of 400 to 1500 kg/c. - using P13T film or polyethylene naph, tallate film, etc.
1 under the condition that the temperature of the can is about 20℃~110℃
I can do it. In this case, the uniaxial stress that the permalloy film receives from the substrate film is predominantly in the direction of compression in the MD direction, and this is because - the film is stretched due to the tension applied to the film for film transport. It can be understood that the permalloy film is formed in such a state that when the film is removed from the vacuum chamber, the tension is released and a force acting on the permalloy film causes the film to return to its original dimensions. Note that -axial stress means a case where the compressive stress or tensile stress is not uniform in the film plane, for example, when the stress in the MD force direction and the stress in the TD force direction cause in-plane magnetic anisotropy. A state in which there are enough differences to make a difference.

The present invention has been described in detail by taking as an example the stress that a Mo permalloy film receives from a substrate film, but as shown in FIG.
It is clear from the gist of the present invention that when forming a Cr alloy film, it is sufficient to take into account the inverse magnetostrictive effect caused by the stress that the Mo permalloy film receives from both the substrate film and the C0Cr alloy film. Note that the CoCr film has a thickness of about 0.
When the film is as thin as 1 μm, the stress exerted on the Mo permalloy film of approximately 0.3 μm or more by CoCr p:4 is relatively small and can be ignored.

According to the present invention described above, it has become possible to mass-produce soft magnetic films with small in-plane magnetic anisotropy easily and with good control.

[Example 2] A Mo permalloy film (N i 79.6 wt%, Fe 15.4 w
t%, MO5, Owt%) to a thickness of 0.4 μm, and then a 0.12 μm thick 0001 alloy film (
Cr20wt%) was formed. In other words, the PET film with a width of 160 mm is loaded into the supply roll 1, and the PET film with a width of 5 cm
The opening of the mask 6 of the can 5 maintained at 90 degrees Celsius while being fed out at a running speed of /min. MD of up to 30 Gauss.
A Mo permalloy film was continuously formed in a length of 100 m by sputtering the MO pepperloy target 11 in an IPa Ar atmosphere in the presence of a substrate film surface magnetic field parallel to the h direction. Next, change the target 11 to a CoCr alloy, and while feeding it at a running speed of 20 cm/minute,
The temperature of the can 5 was set to 110° C., and C0Cr alloy 11Q was formed on a 70vt portion of the Mo permalloy film in an Ar atmosphere of 0.5pa.

No difference was observed in the magnetic properties (coercive force, magnetic anisotropy) between the Mo permalloy film on which the CoCr alloy film was formed and the single layer Mo permalloy film for comparison. The following describes the characteristics of the Mo permalloy film in the single layer portion. The coercive force of the Mo permalloy film is 1.20e when measured in the MDh direction and 1.50e in the TDH direction,
It showed sufficiently good soft magnetic properties. The magnetostriction constant (λ) of the Mo permalloy film was determined to be +2x10- by the measurement method described above.
It turned out to be 7. In addition, the torque curve measured with a torque magnetometer in a magnetic field of 2 KOe is shown in FIG.
It shows uniaxial magnetic anisotropy approximately expressed as θ, and the magnetic anisotropy constant (Ku) is +4. OX10
20r(1/cc (+ sign indicates MD force direction easy axis of magnetization), and showed sufficiently good small anisotropy.This)(u = + 4.OOx102er
/QC was understood as follows. The anisotropy constant (Kσ) due to the inverse magnetostriction effect is -2.9x 1 from the value of the magnetostriction constant λ and the stress σ that the Mo permalloy film receives from the substrate film.
102er/cc (The minus sign indicates the effect of producing anisotropy in the direction with the TD direction as the axis of easy magnetization.) On the other hand, the film is deposited in a magnetic field in the MD direction, thereby magnetizing the MD. The anisotropic effect with easy axis is approximately +
The anisotropy constant is estimated to be 6.5×10 2 ero /cc. The actually measured Ku is approximately given as the sum of both. In other words, the effect of making the MD direction the axis of easy magnetization mainly due to the anisotropy effect induced in the magnetic field (+6.9X
102 ero/cc) and the inverse magnetostrictive effect (-2,'1
As a result, an MO permalloy film with a small Ktl was obtained as a result of the mutually canceling effects. Further, it can be seen that in the film forming method of this example, a small positive magnetostriction (on the order of 10<-7> or less) is preferable.

The coercive force of the CoCr alloy film measured in the direction perpendicular to the film surface is 5
50Q e, and the coercive force measured in the film plane is 3800
It was e. C of hexagonal crystal (hcp) of C0Cr alloy film
The perpendicular orientation of the axis was also sufficiently good, and the film had good perpendicular magnetic anisotropy.

The lamination medium of CoCr alloy film and MO permalloy film is
．． We punched out a 25-inch flexible disk, placed it in a commercially available jacket, pressed down the curls, and used a vertical head to examine the modulation of one cycle of the playback output at a recording density of 50K B P I, and found that the modulation was 5%. Achieved below target value.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a typical configuration of the perpendicular magnetic recording flexible disk of the present invention, where F is a flexible substrate serving as a support, S is a soft magnetic film Ff, R is a perpendicular magnetic recording layer,
P is a protective layer. FIG. 2 is an explanatory diagram of a winding-type facing target sputtering apparatus used in an example of the present invention, where F is a substrate film;
6 is the mask, P is the opposing target cathode assembly, and S is the anti-scattering cover. 11 is a target (two pieces), 12 is a permanent magnet, and B is a magnetic field (dotted line) formed in the opposing target space. Figure 3 shows Mo with large magnetic anisotropy in an experimental example for comparison.
This is a graph of the torque curve of a permanent film, where the horizontal axis is the angle θ (in degrees) between the measured magnetic field and the MD direction of the sample, and the vertical axis is the torque per unit volume, and the unit is era/
cc) r''. Figure 4 shows the magnetization curve of the MO permalloy film, where the horizontal axis is the measured magnetic field (H: ±2008), the vertical axis is the magnetization (M: arbitrary unit), and the solid line is the direction in the MD direction 9. Measured in the line TD direction. (ω is the MO Permalloy IIQ on the PET film substrate, ttn is the MO Permalloy IIQ after removing the film.
This is the M-H loop of Permalloy discipline. FIG. 5 is a graph of the Mo permalloy membrane torque curve obtained in the example. Patent applicant: Teijin Co., Ltd. Patent attorney: 1) Jun Hiroshi
103 Heaven 3

Claims (4)

[Claims] (1) In a flexible disk in which a soft magnetic layer with a low coercive force of 10 Oe or less and a perpendicular magnetic recording layer are formed on a flexible substrate, the soft magnetism is determined by the torque curve measured in the film plane using a torque magnetometer. L=-Ku・sin2θ(L
is the torque acting per unit volume of the soft magnetic layer, Ku is the magnetic anisotropy constant, and θ is the angle between the axis of easy magnetization in the plane of the soft magnetic film and the measured magnetic field of the torque magnetometer. It can be approximated by
A flexible disk characterized in that it is less than or equal to c. (2) The soft magnetic layer has magnetic anisotropy based on the reverse magnetostriction effect due to the stress that the soft magnetic layer receives from other layers, which cancels out the magnetic anisotropy caused by other causes of magnetic anisotropy. The flexible disk according to claim 1, which is a film that is tropic. (3) In the soft magnetic layer, the magnetic anisotropy generated by the inverse magnetostriction effect is approximately uniaxial magnetic anisotropy, and the absolute value of the magnetic anisotropy constant is greater than 2×10^2 erg/cc; ×
The flexible disk according to claim 2, which has a film smaller than 10^3 erg/cc. (4) The soft magnetic layer is formed by a continuous sputtering device having a facing target cathode or a magnetron sputtering cathode onto the flexible substrate that continuously travels along a rotating can, and has a magnetic field strength of a portion where sputtered particles are deposited. 4. The flexible disk according to claim 3, which is a permalloy film formed under conditions in which the component parallel to the plane is 5 Gauss or more at least once.