JP2000242919A - Floppy disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of cracks in the production of a floppy disk having a high recording density. SOLUTION: In a magnetic recording medium with a flattening layer having 0.1-5.0 μm thickness, a seed layer, a chromium-containing nonmagnetic underlayer having a concentration of chromium in the range of 77-100 at.%, a Co-Cr alloy magnetic layer, a protective layer and a lubricative layer in order on at least one face of a flexible nonmagnetic substrate, the coefficient (ESE) of linear expansion of the metallic seed layer and the coefficient (EUL) of linear expansion of the nonmagnetic underlayer satisfy the relation of |ESE-EUL|/EUL <0.3 and the tensile strength (SSE) of the metallic seed layer and the tensile strength (SUL) of the nonmagnetic underlayer satisfy the relation of SSE/SUL>1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having a high recording density, particularly to a removable magnetic recording medium used for an auxiliary storage device and an image storage device of a computer. The present invention relates to a floppy disk having a flexible support having a high recording density of 1 gigabit or more per square inch as a substrate.

[0002]

2. Description of the Related Art Along with the increase in the capacity of electronic data created by a personal computer or the like, a removable disk comprising a high-capacity magnetic recording medium for storing and backing up a large amount of electronic data is desired. In addition, digital video tapes have been mainly used as ultra-high-density recording media for business use.
There is a demand for recording and playback speed. In view of the above, instead of the current mainstream video tape, a removable disk having an excellent recording / reproducing speed is being studied as a digital recording medium for business use.

However, the support of the existing gigabyte-class high-density magnetic recording medium uses a disk, such as aluminum or glass, or a so-called hard disk. Both heads could be severely damaged. Even in the case of a removable hard disk, the problem of shock resistance has not been solved yet, and it has been an obstacle to use as a recording means in a portable device such as a digital disk camera.

Therefore, by changing the support from a hard disk to a flexible one similar to a floppy disk,
A high-density removable magnetic recording medium using a flexible support having excellent impact resistance as a substrate is desired, which has advantages such as a reduction in the weight of a recording unit and a reduction in damage at the time of a head crash.

[0005] The removable magnetic recording medium has a magnetic layer formed of a ferromagnetic metal or alloy on a substrate.
In particular, in a high-density magnetic recording medium, a ferromagnetic layer formed on the surface of the magnetic recording medium forms a magnetic film by using a vacuum film forming method. However, a removable magnetic recording medium using a flexible support has a problem that cracks occur in the manufacturing process and the medium cannot be used.

[0006]

SUMMARY OF THE INVENTION The present invention provides a removable high-density magnetic recording medium having a flexible support as a substrate, which prevents cracks from occurring in the manufacturing process.
It is an object of the present invention to provide a high quality floppy disk type magnetic recording medium.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a flexible device.
An underlayer and a magnetic layer are provided on at least one surface of the non-magnetic support.
Floppy disk with laminated film, protective film and lubricating film
A seed layer between the flexible support and the underlying layer
This can be solved by: In addition, the flattening layer
The above floppy disk having a thickness in the range of 0.1 to 5 μm.
Isk. The thickness of the flexible support is 30 to 100 μm
Is the above-mentioned floppy disk in the range. Magnetic layer
Is a CoCr alloy having a Cr concentration of 10 to 30 at%.
This is the above-mentioned floppy disk using gold. The underlayer is
Cr alloy with Cr concentration in the range of 77 to 100 at%
This is the above-mentioned floppy disk used. Thickness 30 ~
At least one of the flexible supports in the range of 100 μm
A flattening layer having a thickness in the range of 0.1 to 5 μm,
C with a Cr layer having a Cr concentration in the range of 77 to 100 at%.
Nonmagnetic underlayer made of r alloy, Cr concentration of 10 to 30a
Magnetic layer made of CoCr alloy in the range of t%, protection
Layer, and a lubricating layer, and the seed layer has a thickness of 5 to 5.
The linear expansion coefficient of the seed layer in the range of 100 nm
(E _SE) And the linear expansion coefficient (E_UL) But |
E_SE-E_UL| / E_UL<0.3
Tensile strength (S_SE) And the nonmagnetic underlayer
Tensile strength (S_UL) Is S_SE/ S_UL> 1
It is a floppy disk.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have proposed a flexible non-magnetic support having a structure in which an underlayer, a magnetic film, a protective film and a lubricating film are laminated on at least one surface thereof. It has been found that by providing a seed layer between the support and the underlying layer, it is possible to prevent the occurrence of cracks in the manufacturing process and to provide a floppy disk with stable performance. Further, by forming a specific flattening layer, underlayer, and magnetic layer on the nonmagnetic support, the linear expansion coefficient (E _SE ) of the metal seed layer and the linear expansion coefficient (E _UL ) of the nonmagnetic underlayer can be improved. ) Is | E _SE
−E _UL | / E _UL <0.3, and the relation between the metal seed layer tensile strength (E _SE ) and the non-magnetic underlayer tensile strength (S _UL ) is S _SE / S _UL > 1. The present inventors have found that the use of a material that satisfies the seed layer makes it possible to prevent the occurrence of cracks during the production of the medium, and has reached the present invention. That is, cracks in a ferromagnetic metal thin film formed on a substrate using a flexible material as a non-magnetic support are formed by a flatness required for a high-density magnetic recording medium and a seed layer formed thereon. It has been found that it is caused by thermal expansion of an underlayer or the like.

When a hard disk made of aluminum, glass or the like is used as a support, flatness close to a mirror surface can be produced by polishing or the like. However, in the case of a floppy disk, since a flexible support is used as a support, it is difficult to improve flatness by polishing. Therefore, by providing a flattening layer made of a polymer substance on the flexible support, the same surface properties as those of the hard disk support are realized. A non-magnetic underlayer and a magnetic layer are formed on the flattening layer by sputtering, but it is necessary to heat the support at a high temperature of 100 to 300 ° C. in order to enhance the magnetostatic characteristics and electromagnetic conversion characteristics of the magnetic layer. Occurs. Alternatively, the use of bias application, RF sputtering, or the like effectively increases the temperature of the support. The medium on which the nonmagnetic underlayer and the magnetic layer are formed is cooled to room temperature and taken out of the sputtering apparatus. In such a manufacturing process in which the temperature changes, the flexible support, the planarizing layer, the nonmagnetic underlayer, and the magnetic layer undergo thermal expansion and contraction.

In the hard disk, since the support is made of a hard material and the material is made of metal, ceramics, glass, or the like, the difference in the expansion coefficient between the underlayer and the support is small. Although the possibility of cracks or the like occurring in the heating and cooling steps based on the difference in thermal expansion was small, in the case of a magnetic recording medium using a flexible support as a substrate, the flexible support, The layer is formed of a polymer composition, and since the non-magnetic underlayer and the magnetic layer are metallic materials, the amounts of thermal expansion and contraction differ between the two by about one digit. Therefore, it is considered that the nonmagnetic underlayer material cannot withstand the deformation of the support during cooling, and cracks are generated in the magnetic recording medium.

Therefore, by providing a nonmagnetic underlayer, that is, a seed layer between the flat layer and the underlayer, the underlayer and the seed layer receive the force between the flat layer and the underlayer generated when the support is cooled, and the film strength is improved and the cracks are improved. Can be prevented. In addition, the linear expansion coefficient (E _SE ) of the seed layer and the linear expansion coefficient (E _UL ) of the under layer as the material of the seed layer and the under layer are | E _SE- E _UL
| / E _UL <0.3, the seed layer tensile strength (S _SE ) and the underlying layer tensile strength (S _UL ) are S _SE / S
By selecting a forest material that satisfies the relationship of _UL > 1, it is possible to counteract the force generated by the difference in the coefficient of linear expansion between the underlayer and the magnetic layer during the cooling process, and to prevent cracks at a higher level It is thought that it is possible. That is, in a floppy disk having a structure in which an underlayer, a magnetic film, a protective film, and a lubricating film are laminated on at least one of the flexible supports, a seed layer is provided between the flexible support and the underlayer, so that a medium can be formed at the time of producing a medium. An object of the present invention is to provide an ultra-high-density floppy disk by preventing cracks from occurring.

That is, according to the present invention, the linear expansion coefficient (E _SE ) of the metal seed layer and the linear expansion coefficient (E _UL ) of the nonmagnetic underlayer are set to | E in order to prevent cracks occurring during the above-mentioned steps.
The relationship of _SE− E _UL │ / E _UL <0.3 is satisfied, and the relationship between the seed layer tensile strength (S _SE ) and the non-magnetic underlayer tensile strength (S _UL ) is S _SE / S _UL > 1. By providing a metal seed layer that satisfies the above condition, it is possible to prevent cracks generated at the time of producing a medium and to provide a high recording density floppy disk.

Next, preferable materials and the like which can be used in the present invention will be described. Examples of the support of the magnetic recording medium of the present invention include materials such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide, and polybenzoxazole. Further, the Young's modulus of the support of the magnetic recording medium of the present invention is preferably from 200 to 1600 kg / mm ² ,
Particularly desirable is 300 to 800 kg / mm ² . The thickness of the support is preferably from 20 to 150 μm, and more preferably from 30 to 80 μm.

In order to improve the flatness of the surface of the support, a flattening layer is provided on the support. In the planarization layer,
A heat-resistant polymer material can be widely used. Particularly preferred are materials such as silicone resin, polyamide resin, polyamideimide resin, and polyimide resin. These materials are not only excellent in heat resistance, but also can achieve good surface properties and magnetostatic properties. The coating thickness of the flattening layer is 0.1 to 5.0 μm, preferably 0.5 to 5.0 μm.
3.0 μm, particularly preferably in the range of 0.8 to 2.0 μm.

On the surface of the flattening layer, minute projections such as SiO
₂ , inorganic fine particles such as Al ₂ O ₃ and TiO ₂ or organic fine particles may be provided. The particle size of the fine particles used for forming the fine projections is preferably 5 to 40 nm, more preferably 10 to 35 nm, and further preferably 15 to 30 nm. The height of the protrusion formed on the surface of the flattening layer is preferably 30 nm or less. The particle size of the fine particles formed on the surface of the flattening layer is 5
If it is less than nm, the effect due to the presence of the fine particles on the surface of the flattening layer cannot be obtained, and if it is more than 40 nm, the layer formed thereafter will have irregularities and the flatness will be reduced.

The seed layer formed between the planarizing layer and the underlayer is made of Ta, Mo, W, V, Zr, Cr, Rh, Hf, N
Among b, Mn, Ni, Al, Ru and Ti, an alloy containing at least one kind of metal or two or more kinds of elements is preferable. Further, oxygen, nitrogen and the like may be contained.

The thickness of the seed layer is 10 nm to 100 nm.
And more preferably 15 to 80 n
m, more preferably 20 to 60 nm. When the thickness of the seed layer is reduced to 10 nm or less, the structure of the seed layer becomes discontinuous, and a force generated by heat shrinkage is applied to the underlayer, thereby causing cracks. When the thickness is more than 100 nm, cracks, film peeling, etc. occur in the magnetic recording medium due to the film stress of the seed layer. The seed layer can be formed by DC sputtering in an argon atmosphere.
The seed layer forming temperature is 5 to 250 ° C, preferably 10 to 200 ° C.

The material of the nonmagnetic underlayer is chromium, or chromium and Ti, W, Mo, V, Ta, B, Si, N
An alloy containing at least one metal of b, Zr, Al and Mn is preferable. The Cr concentration of the nonmagnetic underlayer is 7
It is 7 to 100 atomic%, preferably 80 to 95 atomic%, and the balance is other elemental metals. The thickness of the nonmagnetic underlayer is 5 nm to 500 nm, preferably 10 to 100 nm.
nm. When the thickness of the underlayer is increased to 500 nm or more, the grain size of the magnetic layer increases, and the medium noise increases.

The linear expansion coefficient (E _SE ) of the metal seed layer and the linear expansion coefficient (E _UL ) of the non-magnetic underlayer formed by the above method are | E _SE −E _UL | / E _UL <0. It is necessary to provide a metal seed layer that satisfies the relationship of (3) and the tensile strength of the seed layer (S _SE ) and the tensile strength of the nonmagnetic underlayer (S _UL ) satisfy the relationship of S _SE / S _UL > 1. Become. More preferably, the relationship | E _SE −E _UL | / E _UL <0.2 is satisfied, and S _SE / S _UL > 1.1.

Further, a seed layer satisfying the above relationship,
The non-magnetic underlayer is made of Ta (film thickness: 20 nm, input power: 11.4 W / c) as a seed layer material.
m ² , partial pressure of argon: 8 mTorr), CrTi ₂₀ (film thickness: 60 nm, input power: 11.4) as a nonmagnetic underlayer material
(W / cm ² , partial pressure of argon: 15 mTorr).

As the magnetic material forming the magnetic layer, a cobalt chromium alloy is preferable, and particularly, Pt, Ta, Ni, S
Cobalt-chromium alloys containing i, B, Ni, and Pd, and those containing oxygen are also included. Among these, CoCrPt and CoCrPtTa are particularly preferred. These are because both the output and the noise characteristics are excellent. Barium ferrite other than the cobalt chromium alloy can be used. The Cr concentration in the ferromagnetic layer is 1
0 to 30 atomic%, preferably 12 to 28 atomic%,
More preferably, it is 15 to 25 atomic%. The thickness of the magnetic layer is 10 to 300 nm, preferably 10 to 60 nm. The nonmagnetic underlayer and the magnetic layer are preferably provided by a vacuum film forming method. In particular, sputtering is preferable because a film can be formed without changing the composition of elements. Also, a seed layer,
It is preferable to form films continuously in a vacuum state for both the underlayer and the magnetic layer.

On the magnetism, a plasma CV
It is preferable to provide a carbon film made of an amorphous structure, a graphite structure, a diamond structure, or a mixture thereof prepared by the method D, the sputtering method, or the like. Particularly preferred is a hard amorphous carbon film generally called diamond-like carbon. This hard carbon film has a Vickers hardness of 1000 kg / mm ² or more, preferably ² kg / mm ² or more.
It is a hard carbon film of 000 kg / mm ² or more. The thickness of the protective film is preferably 2.5 to 30 nm, particularly preferably 5 to 25 nm.

In the magnetic recording medium of the present invention, in order to improve running durability and corrosion resistance, it is preferable to add a lubricant or a rust inhibitor to the magnetic film or the protective film. As the lubricant, known hydrocarbon-based lubricants, fluorine-based lubricants, extreme pressure additives and the like can be used. Examples of the hydrocarbon-based lubricant include carboxylic acids such as stearic acid and oleic acid, esters such as butyl stearate, sulfonic acids such as octadecylsulfonic acid, phosphoric esters such as monooctadecyl phosphate, stearyl alcohol, oleyl alcohol and the like. Alcohols, carboxylic acid amides such as stearic acid amide, and amines such as stearylamine.

Examples of the fluorine-based lubricant include lubricants in which part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group. Examples of the perfluoropolyether group include a perfluoromethylene oxide polymer, a perfluoroethylene oxide polymer, a perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , and a perfluoroisopropylene oxide polymer (CF ( CF ₃ ) C
F ₂ O) _n or a copolymer thereof.

Examples of extreme pressure additives include phosphoric esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphoric esters such as trilauryl trithiophosphite, and the like. And sulfur-based extreme pressure agents such as dibenzyl sulfide.

The above lubricants are used alone or in combination of two or more. As a method of applying these lubricants on a magnetic film or a protective film, a lubricant is dissolved in an organic solvent and applied by a wire bar method, a gravure method, a spin coating method, a dip coating method, or a vacuum evaporation method. What is necessary is just to make it adhere. The amount of the lubricant to be applied is 1 to 30 mg / m ^2.
Preferably, 2 to 20 mg / m ² is particularly preferred.

The rust preventives usable in the present invention include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives having an alkyl side chain introduced into the mother nucleus, benzothiazole, 2-mercapto. And nitrogen- and sulfur-containing heterocycles such as benzothiazole, tetrazaindene ring compounds and thiouracil compounds, and derivatives thereof.

[0028]

The present invention will be described below with reference to examples and comparative examples of the present invention. Example 1 A polyimide resin having a thickness of 1 μm was applied as a flattening layer on a 75 μm polyimide flexible support, and a partial pressure of 8 mTorr of argon and a power supply of 11.4 W / cm were formed thereon as a seed layer.
^2. Tantalum was coated to a thickness of 20 nm by DC sputtering at a substrate temperature of 20 ° C. Further, as a non-magnetic underlayer, titanium was applied at a partial pressure of 15 mTorr, an applied power of 11.4 W / cm ² and a support temperature of 200 ° C.
A chromium alloy containing 0 atomic% was coated to a thickness of 60 nm by a direct current sputtering method.

Next, as a magnetic layer on the non-magnetic underlayer, an argon partial pressure of 1.5 mTorr, an input power of 11.4 W / cm ² ,
At a support temperature of 200 ° C., a 30 nm-thick Co alloy thin film containing 20 atomic% of Cr and 12 atomic% of Pt was formed by DC sputtering. Next, a 20 nm-thick carbon protective film was provided on the magnetic layer by DC sputtering under the conditions of an argon partial pressure of 3 mTorr and an input power of 5.71 W / cm ² .

Further, as a lubricant, a solution obtained by dissolving monolauryl phosphate (CH ₃ (CH ₂ ) ₁₁ OPO ₃ H ₂ ) and amine stearate (CH ₃ (CH ₂ ) ₁₇ NH ₂ ) in methanol was used. The acid and the amine were applied by a wire bar method so that the molar ratio of the acid and the amine was 1: 1 and the applied amount of both was 6 mg / m ² to prepare a floppy disk.

Examples 2 to 6 Example 1 was repeated except that the material of the seed layer described in Example 1 or the material of the nonmagnetic underlayer was changed to those shown in Table 1.
The floppy disks of Examples 2 to 12 produced in the same manner as described above were produced.

Comparative Example 1 Comparative Example 1 was performed in the same manner as in Example 1 except that no seed layer was provided.
Was prepared.

Comparative Examples 2 to 11 Comparative Examples 2 to 11 were performed in the same manner as in Example 1 except that the material of the seed layer described in Example 1 was changed to the material described in Table 1.
Was prepared.

The obtained magnetic recording media of Examples and Comparative Examples were measured by the following measurement methods, and the measurement results are shown in Table 1. (Measurement Method) (1) Linear Expansion Coefficient The linear expansion coefficient is measured using a sputtering apparatus (S-50S manufactured by Shibaura Seisakusho) and heating the sample to 300 ° C. with a lamp heater under a vacuum of 10 ⁻⁶ Torr or less. ,
The amount of deformation of the sample was determined from a strain gauge (Strain gauge WK manufactured by Micro Measurement Co., Ltd.) attached to both surfaces of the sample. The sample used had a size of 5 mm × 30 mm in which a single layer was formed on both sides of the polyimide support. In order to remove the influence of the deformation of the support, a strain gauge was attached to only the polyimide support, and the amount of deformation of the sample was measured. The deformation amount Vsp of the film-formed sample and the deformation amount Vpi of only the polyimide support are measured, and the difference (Vsp-Vpi) between the two is defined as the deformation amount of the formed film, and the following equation is used. (Vsp-Vpi) / sample length / temperature difference.

(2) Tensile Strength A 5 mm × 30 mm sample obtained by forming a single layer on both sides of the polyimide support under the conditions described in Examples and Comparative Examples was applied to a tensile tester (Tensilon STM- manufactured by Toyo Boring Co., Ltd.).
T-50BP), the surface of the formed film was observed with a microscope at a magnification of 200 times, and the load at which cracks occurred was defined as the tensile strength. (3) Crack After the protective film was formed by sputtering, the surface of the cooled sample was examined with a differential interference microscope (Nikon XP).
(U) Observe by NR-A). The magnification is 200 times, and 30 observations are made at random. If no crack was observed during the 30 measurements, it was regarded as “excellent”, and if it was within two places, it was regarded as “good”, and if it was more than 2 points, it was regarded as “bad”.

[0036]

[Table 1] Underlayer E _UL S _UL sheet ゛ E _SE S _SE Expansion ratio Strength ratio Crack Example 1 CrTi ₂₀ 6.9 38.4 Ta 6.5 53.0 0.13 1.38 Excellent Example 2 CrTi ₂₀ 6.9 38.4 Mo 5.1 49.0 0.26 1.28 Excellent Example 3 CrTi ₂₀ 6.9 38.4 Rh 8.5 54.9 0.23 1.43 Excellent Example 4 CrMo ₂₀ 6.2 43.0 Ta 6.5 53.0 0.04 1.23 Excellent Example 5 CrMo ₂₀ 6.2 43.0 Mo 5.1 49.0 0.18 1.13 Excellent Example 6 CrTi ₂₀ 6.9 38.4 CrTi ₂₅ 6.3 39.2 0.09 1.00 Good Example 7 CrTi ₂₀ 6.9 38.4 Zr 5.0 35.0 0.27 0.91 Good Example 8 CrTi ₂₀ 6.9 38.4 Nb 7.2 21.0 0.04 0.73 Good Example 9 CrTi ₂₀ 6.9 38.4 Ir 6.8 20.3 0.01 0.53 Good Example 10 CrTi ₂₀ 6.9 38.4 Mn 23.0 50.4 2.33 1.31 Good Example 11 CrTi ₂₀ 6.9 38.4 Al 23.5 4.76 2.41 0.13 Good Example 12 CrMo ₂₀ 6.2 43.0 Rh 8.5 54.9 0.37 1.27 Good Comparative Example 1 CrTi ₂₀ 6.9 38.4-----Poor Comparative Example 2 CrMo ₂₀ 5.8 43.0-- ---Defective Comparative Example 3 Cr 6.2 42.0-----defective Comparative Example 4 Rh 8.5 54.9-----defective Comparative Example 5 Zr 5.0 35.0-----defective ratio Example 6 Ta 6.5 53.0-----Poor Comparative Example 7 Mo 5.1 49.0-----Poor Comparative Example 8 Mn 23.0 50.4-----Poor Comparative Example 9 Al 23.5 4.76-----Poor Comparative Example 10 Mo 5.1 49.0-----Bad Comparative Example 11 CrTi ₂₀ 6.3 39.2-----Bad

In Table 1, E _UL : Underlayer linear expansion coefficient Unit: 10 ^-6 S _UL : Underlayer linear tensile strength Unit: kg / mm ² E _SE : Seed layer linear expansion coefficient Unit: 10 ^-6 S _SE : Tensile strength of seed layer Unit: kg / mm ² Expansion ratio: | E _SE -E _UL | / E _UL Strength ratio: S _SE / S _UL

[0038]

According to the present invention, a flattening layer formed on a flexible support,
A seed layer is provided between the nonmagnetic underlayer provided as the underlayer of the magnetic layer, and the linear expansion coefficient and the tensile strength of the seed layer and the nonmagnetic underlayer are set to specific values. It is possible to prevent the occurrence of cracks due to thermal expansion due to temperature rise and cooling during manufacturing, and to stably manufacture a magnetic recording medium for high recording density.

Claims (7)

[Claims] 1. A floppy disk having a structure in which an underlayer, a magnetic film, a protective film, and a lubricating film are laminated on at least one surface of a flexible nonmagnetic support, a seed layer is provided between the flexible support and the underlayer. A floppy disk characterized by being provided. 2. The method according to claim 1, wherein a flattening layer made of a heat-resistant polymer is provided on the flexible non-magnetic support.
The floppy disk described. 3. The method according to claim 1, wherein the thickness of the planarizing layer is in a range of 0.1 to 5 μm.
Floppy disk according to the item. 4. The thickness of the flexible support is 30 to 100 μm.
The floppy disk according to any one of claims 1 to 3, characterized in that: 5. The floppy disk according to claim 1, wherein the magnetic layer is made of a CoCr alloy having a Cr concentration in a range of 10 to 30 at%. 6. The underlayer having a Cr concentration of 77 to 100 at%.
The floppy disk according to any one of claims 1 to 5, wherein a Cr alloy in the range of (1) is used. 7. A flexible support having a thickness in the range of 30 to 100 μm is provided on at least one surface of the flexible support in a thickness of 0.1 to 5 μm.
m, a flattening layer, a seed layer, and a Cr concentration of 77 to
Non-magnetic underlayer made of a Cr alloy in the range of 100 at%, CoCr having a Cr concentration in the range of 10 to 30 at%
A magnetic layer made of an alloy, a protective layer, and a lubricating layer,
The thickness of the seed layer is in the range of 5 to 100 nm, and the linear expansion coefficient (E _SE ) of the seed layer and the linear expansion coefficient (E _UL ) of the nonmagnetic underlayer are | E _SE −E _UL | / E _UL < 0.3, and the tensile strength (S _SE ) of the metal seed layer and the tensile strength (S _UL ) of the non-magnetic underlayer are S _SE / S _UL > 1.
A floppy disk characterized by satisfying the following relationship: