JPS6037974B2 - Improved magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new magnetic recording medium, and more particularly to a magnetic recording medium having a magnetic coating layer in which magnetic particles mainly composed of Mn and Bi are dispersed in an organic binder as a magnetic recording layer. It is something.

The conventional magnetic recording material is maghematite (y-Fe203)
, Co-doped maghemite
Two Fe203), magnetite (Fe304), y-
Magnetic powders such as bertolide compounds of Fe203 and Fe304, chromium dioxide (C2), or ferromagnetic alloys mainly composed of transition metals such as Fe, CO, and Ni are dispersed in an organic binder and placed on a nonmagnetic support. A magnetic layer formed by coating has been used.

However, the coercive force of the magnetic layer of these magnetic recording bodies is usually 300 to 80 e at room temperature, and 120 is a moderate value at most. It has not been put to practical use, partly because it is extremely difficult to write magnetic signals using electromagnetic transducers. However, in recent years, with the spread of the application of magnetic recording, magnetic recording bodies are not only used under controlled environments like conventional magnetic tapes for broadcasting and computers, but also magnetic tapes for general household use, banks, transportation, etc. They are now being used even in harsh environments, such as institutional magnetic cards. In particular, in the case of magnetic cards, etc., even a part of the written magnetic signals must not be accidentally erased by an external disturbing magnetic field, and it is desirable to have a magnetic recording medium that prevents the magnetic signals once written from being erased. was.

Furthermore, with the development and introduction of various electrical devices in magnetic recording media for broadcasting, measurement, and computers, there is an increasing chance that information on the magnetic recording media will be lost due to external disturbance magnetic fields from these devices. Since conventional magnetic recording media do not have high coercive force, written magnetic signals are erased by external disturbing magnetic fields, resulting in the problem that magnetic recording and reproducing devices malfunction. In order to solve this problem, we have developed a magnetic material that has a magnetic layer that has a tendency for coercive force to increase as the temperature rises in the temperature range below room temperature, and has a coercive force of 150 pio or more near room temperature. A recording medium is proposed.

Examples of such magnetic materials include magnetic materials that have a large magnetocrystalline anisotropy constant near room temperature and whose magnetocrystalline anisotropy constant decreases when cooled below room temperature, such as MnBi.
Or MhBi added with Ti, Sb, etc.; Fe≧≠x
T + Fe, -x)04 (0.04<xmi0.1):
BaFe, 20.9 or S added with Co, Ti, etc.
This is a magnetic layer made of rFe, 20, 9, etc. formed in the form of a thin film, or a coated magnetic layer made of single-domain particles dispersed in an organic binder. The temperature characteristics of these coercive forces can be changed depending on manufacturing conditions, particle size, amount of additives, etc. Furthermore, magnetic materials exhibiting an antiferromagnetism-ferrimagnetism transition at low temperatures below around room temperature, such as Mn2-×CrxSb.
(0.01 < × Mi 0.08), acicular single domain particles such as FeRh, MnGa○, etc. added with Pd, V, Mn, Au, etc., whose coercive force is obtained by the effect of shape anisotropy. There is a magnetic layer made by dispersing and coating magnetic particles in an organic binder. Among these, magnetic particles mainly composed of Mn and Bi have a coercive force of more than 1000 e at room temperature, but at low temperatures such as liquid nitrogen (~-196℃)
In the vicinity, materials with coercive forces of 10 or less have been obtained, making them excellent magnetic materials.

However, even if Mn-Bi magnetic particles are dispersed in a temporary organic binder, they are sensitive to moisture and are gradually oxidized even at room temperature, and in extreme cases they lose their magnetism, making them unsuitable for practical magnetic recording media. has not been obtained.
The object of the present invention is to provide a magnetic recording medium having moisture-resistant and oxidizable Mn--Bi magnetic particles that has improved this drawback. The present inventors have discovered that the above object can be achieved in a magnetic recording material containing Mn-Bi magnetic particles as the main component of the magnetic layer by coating the magnetic particles with a layer containing the chromium of the particles. This invention has been achieved. Chromium coating M in the present invention
nBi magnetic particles are produced by preparing MnBi powder and then contacting it with chromium ions, chromate ions, or dichromate ions in water or water containing a polar solvent.

It is desirable to chromium-treat the surface of fresh M old i-based particles that have not been produced for much time. Chromium compounds used in the present invention include chromium chloride, potassium chromium sulfate (chromium alum), sodium chromate, chromic acid, potassium chromate, sodium dichromate, potassium dichromate, ammonium dichromate, etc. .
The use of chromium compounds for the purpose of improving the corrosion resistance of metals has been known for a long time, including chromate treatment of iron plates.

Others, such as U.S. Patent Nos. 65627 and 3837.
No. 912, No. 3932293, No. 3157532, etc. describe the treatment of Fe (Co, Ni) based alloy powder. However, all of these are metalloids B
There is no mention of chromium treatment for MnBi-based magnetic powder containing a large amount of i, and it was completely unexpected that chromium treatment is also effective for semimetals. In the present invention, it is desirable that the chromium compound be dissolved in water or a mixed solvent of water and a sacrificial solvent in an amount of 0.5 to 1% by weight.

Below the lower limit, the effect of improving weather resistance is small, and above the upper limit, the magnetization os of the M old i particles decreases. 300 to 2000 per 10 parts by weight (hereinafter referred to as parts by weight) of MnBi powder
It is desirable to use the above-mentioned processing solution and sufficiently remove the M and I powder in the processing solution.

Application of ultrasonic waves, application of an alternating magnetic field, cut-off type dispersion, etc. are particularly effective for uniformly treating particles with chromium. Desirably, the treatment time is 3 to 20 minutes; below the lower limit, the chromium treatment tends to be uneven, while above the upper limit. A decrease in s occurs. The processing temperature is preferably 0.000 to 60 qo, and if the temperature exceeds the upper limit, the processing time must be shortened. s tends to decrease, and if the time is shortened, the processing tends to become non-uniform. Through such treatment, M-type magnetic powder having a surface layer containing Cr-Mn-Bi-○ is obtained.

As mentioned above, the amount of Cr contained in the powder is 1.5 to 5% by weight, and if the amount of Cr is less than this, the weather resistance tends to decrease, and if the amount of Cr is large, the weather resistance tends to decrease. s tends to decrease. It is also effective to further add a rust preventive agent to the alloy powder of the present invention or to perform hydrophobization treatment with a surfactant.

Anionic surfactants are suitable as surfactants used for hydrophobization treatment, and examples of anionic surfactants include those having a carboxylate salt in the hydrophilic group, those having a sulfate ester salt, those having a phosphate ester salt, Examples include those containing dithiophosphoric acid ester salts and those containing sulfonate salts.

Here, salts include ammonium, alkali metals (Li, Na
, K, etc.) and salts of alkali metals (Mg, Ca, Ba, etc.). Furthermore, fatty acids can also be used although they are not surfactants. As the organic binder used for coating the Mn-Bi magnetic material, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

Regarding the manufacturing method of the magnetic paint used in the present invention,
-186, 47-28043, 47-28045, 47-28046, 47-28048, 47-3
It is described in detail in publications such as No. 1445.

The magnetic paints described in these documents mainly contain ferromagnetic powder, binder, and coating solvent, and may also contain additives such as dispersants, lubricants, abrasives, and antistatic agents.
As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

As a thermoplastic resin, the softening temperature is 150 oo or less, the average molecular weight is 10,000-200,000, and the degree of polymerization is about 200-200.
2,000 or so, such as vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer,
Methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer,
Polyvinyl fluoride, vinyl chloride IJ desoacrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (
Cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various synthesis Rubber-based thermoplastic resins and mixtures thereof are used.

Examples of these resins include Japanese Patent Publications No. 37-6877, No. 39-12528, No. 39-19282, No. 40-534y, No. 40-20907, No. 41 Isuke No. 63, and No. 41-140.
No. 59, No. 41-16985, No. 42-6428, 42
111621, 43-4623, 43-15206
No. 44-288y, No. 44-17947, 44-1
No. 8232, No. 45-1402, No. 45-14500, No. 47-18573, No. 47-22063, No. 47-2
No. 2064, No. 47-22068, No. 47-22069, No. 47-2207, No. 48-27886, U.S. Patent No. 3144352; No. 3419420: No. 34
No. 99789; described in the specification of No. 3713887.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, but when added after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate These include mixtures of polymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof. Examples of these resins include Samurai Kosho No. 39-18103, No. 40-19779, No. 41-7192, No. 41-8016, No. 41-14275,
42-1817y, 43-12081, 44-28
No. 023, No. 45-14501, No. 45-24902,
46-13103, 47-22065, 47-22
No. 066, No. 47-22067, No. 47-22072,
No. 47-22073, No. 47-28045, 47-28
No. 048, Publication No. 47-28922, U.S. Patent No. 314
No. 4353: No. 3320090: No. 3437510; No. 3597273: No. 378121; No. 378
It is described in the specification of No. 1211.

These binders may be used alone or in combination;
Another additive may be added.

The mixing ratio of the ferromagnetic powder and the binder is 10 to 40 parts by weight, preferably 30 to 20 parts by weight, per 100 parts by weight of the ferromagnetic powder. In addition to the above-mentioned binder and fine ferromagnetic powder, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent may be added to the magnetic recording layer.

Dispersants include caprylic acid, capric acid, lauric acid,
Fatty acids with 12 to 18 carbon atoms such as myristic acid, valmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid (R, COO, R, is a fatty acid with 11 to 17 carbon atoms) Alkyl group): Metal soap consisting of alkali metals (Li, Na, K, etc.) or alkali metals (Mg, Ca, mother) of the above-mentioned fatty acids; lecithin, etc. are used.

In addition to these, higher alcohols having a carbon number of 1a or less, and sulfuric acid esters may also be used. These dispersants are added in an amount of 1 to 2 parts by weight based on 10 parts by weight of the binder. Lubricants include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of a monobasic fatty acid with 12 to 1 carbon atoms and a monohydric alcohol with 3 to 12 carbon atoms, and carbon atoms. A fatty acid ester consisting of 17 or more monobasic fatty acids and a monohydric alcohol having a total of 21 to 2 carbon atoms can be used.

These lubricants are used in an amount of 0.2 to 10 parts by weight of the binder 10.
It is added in an amount of 20 parts by weight. Regarding these, the specifications of Japanese Patent Publication No. 43-2388 Nogure Publication, Japanese Patent Application No. 42-28647, Samurai Application No. 43-81543, etc., U.S. Patent No. 3
No. 470021; No. 3492235: No. 349741
No. 1: No. 3523086; No. 3623760: No. 3
No. 630772: No. 3634253: No. 364253
Reference number: 3687725; “IBM Tech
nical Disclosme Bulletin”
Vol. 9, No. 7, Pa bag 779 (196
December 6): “ELEKTRONIK'1961
Year, M. 12, Page 38 Toge et al.' are described.
Commonly used abrasive materials include fused alumina,
Silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are used.

These abrasives have an average particle diameter of 0.05 to 5 A, particularly preferably 0.1 to 2 A. These abrasives are used in an amount of 7 to 2 parts by weight based on 10 parts by weight of the binder.
It is added in a range of parts by weight. Regarding these, Japanese Patent Application No. 48-26749, U.S. Patent No. 3007807
No.: 3041196, 3293066; 36
30910, 3687725; British Patent No. 114
534 cry; West German patent (DT-PS) 853211
It is stated in the specification of the No. Natural surfactants such as Sanipon as antistatic agents; nonionic surfactants such as alkylene oxide, glycerin, and glycidol;
Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; Contains acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate ester groups, phosphate ester groups, etc. Anionic surfactant: Ampholytic surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. Some of these surfactant compounds that can be used as antistatic agents are disclosed in U.S. Pat.
No. 71623, No. 2240472, No. 2288226
No. 2676122, No. 2676924, No. 26
No. 76975, No. 2691566, No. 2727860
No. 2730498, No. 2742379, No. 27
No. 39891, No. 3068101, No. 3158484
No. 3201253, No. 3210191, No. 32
No. 94540, No. 3415649, No. 3441413
No. 3442654, No. 3475174, No. 35
No. 45974, West German Patent Publication (OLS) 19426
No. 65, British Patent No. 1077317, British Patent No. 119845, etc., as well as Ryohei Oda et al.'s "Synthesis of Surfactants and Their Applications" (Yoko Shoten 1964 King Edition): AW. Bay IJ
Author: “Surface Active Agents” (Interscience Publications Inc. 195#)
Wang version); T. P. “Encyclopedia” by Sisley
"Of SurfS Active Agency, Volume 2" (Chemical Publishing Company - 1964 hand edition):
“Surfactant Handbook” 6th edition (Sangyo Tosho Co., Ltd., 1939)
It is written in books such as December 20, 1999).

These surfactants may be added alone or in combination.

These are used as antistatic agents, but are sometimes used for other purposes, such as dispersion, improving magnetic properties,
It may also be used to improve lubricity and as a coating aid.
To form the magnetic recording layer, the above-mentioned composition is dissolved in an organic solvent and applied as a coating solution onto a support.

Methods for applying the magnetic recording layer onto the support include air doctor coating, plaid coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, and spray coating. can be used, and other methods are also possible, and detailed explanations of these can be found in "Coating Engineering" published by Asakura Shoten, pages 253-277.
It is described in detail on the page (published by Shintakugyo on March 2, 1972). Organic solvents used during coating include ketone types such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol types such as methanol, ethanol, propanol, and butanol; methyl acetate,
Ester types such as ethyl acetate, butyl acetate, ethyl lactate, and glycomonoethyl acetate; glycol ether types such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene, toluene, xylene, etc. Tar type (aromatic hydrocarbons); methylene chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, and dichlorobenzene can be used. By such a method, the magnetic layer coated on the support is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried.

Further, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary. In this case, the orientation magnetic field is approximately 500 to 2000 AC or DC.
Gauss, and the drying temperature is about 50 to 100℃.
Drying time is approximately 3 to 1 minute.

These include, for example, Japanese Patent Publication No. 39-128368, No. 40-
No. 23625, US Patent No. 347396, etc. Furthermore, the method disclosed in Japanese Patent Publication No. 13181/1986 is considered to be a basic and important technique in this field. Polyesters such as polyethylene terephthalate and polyethylene naphthalate are used as supports.
Polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polycarbonate,
The base material may be a plastic material such as polyimide, a metal such as aluminum, copper, yellow steel, titanium, stainless steel, or an inorganic material such as glass or ceramic.

The shape of the base may be tape, sheet, card, disk, or drum. In the case of a tape or sheet, the thickness of the support is about 5 to 50 cm, preferably 1
Approximately 0 to 40 French m is good; in the case of a card or disk shape, about 0.1 to 5 French m is good.

The above-mentioned support is coated with a so-called back coat (ba
ckcoat).

Regarding the back coat, for example, U.S. Patent No. 28044
No. 01, No. 3293066, No. 3617378, No. 3062676, No. 3734772, No. 34765
No. 96, No. 2643048, No. 2803556, No. 2887462, No. 2923642, No. 29974
No. 51, No. 3007892, No. 3041196, No. 311542, No. 31666, etc. In addition, the form of the support is tape, sheet, card,
It may be a disk, a drum, or the like, and various materials are selected as necessary depending on the form.

Of course, conventionally known techniques such as providing a protective layer on the Mvalent i magnetic layer can also be combined.

The present invention will be explained in more detail below using examples.

It will be readily understood by those skilled in the art that the components, proportions, order of operations, etc. shown herein may be changed without departing from the spirit of the invention. Therefore, the invention should not be limited to the examples below.

In addition, in the following examples, all parts indicate parts by weight. The composition of the Mn-Bi magnetic particles used in the present invention is as follows:
Generally, Mn/Bi is preferably 8/2 to 4/6 (atomic ratio), particularly preferably 6/4 to 5/6, in view of the conditions that require sufficient saturation magnetization as a magnetic material for magnetic recording media.
5 (atomic ratio).

In addition, the particle size is generally 10 m or less, particularly preferably 3 m or less, in order to obtain the desired coercive force and S/N ratio.
It is as follows. Particularly preferably 1.5 m or less, 100A
That's all. MnBi powder is obtained by crushing MnBi lumps.

Grinding can be carried out using various mills (sand mill, hammer mill, ball mill), etc. For the M old i particle,
Others Ru, Rh, Pd, false, Sb, A〆, Ga, Ge
, ln, T, P, Sn, Pb, Ti, and lr can also be added as minor components of 20 mol % or less. Example 1 Mn powder and Bi powder suitable for a 60-mesh sieve were mixed, molded using a press, held at 700°C for 2 hours in argon gas, and then held at 350 qo for 7 days.

After cooling slowly, the mixture was pulverized using a high-speed hammer mill in an argon gas atmosphere. The M old i powder thus obtained was ball milled with the following composition while keeping air out. Ball mill time is 2
It's immediate. As the ball mill progresses, it becomes fine powder,
In addition, it was observed that the powder form was broken into hexagonal plate shapes.

The average particle size is 0.75 fm, 0.4 mm to u
Particles between rm are present. After ball milling, the slurry was centrifuged in N2, and 205 parts of the resulting acetone-containing cake (containing 10 parts of MnBi powder) was added to the next chromium treatment solution without contact with air, and vigorously stirred for 5 minutes. I prayed for a minute. The temperature of the treatment liquid was 25°C. After the Nada frame, the magnetic powder was centrifuged.

Next, add 200 ml of distilled water (boiled and degassed) to the cake in the centrifuge, then add 4 ml of acetone.
00 parts of butyl acetate was poured into the solution three times, and 30 parts of butyl acetate was poured once, followed by washing with water, dehydration, and solvent replacement. Finally, after separating off the butyl acetate, the cake was transferred into the next composition. The treatments up to this point are performed in nitrogen. The cake contains 100 parts of M old i powder and 11 parts of butyl acetate. (cf.1):
It is made by the reaction of epichlorohydrin and diphenylpropane and has a molecular weight of approximately 100 u and an epoxy equivalent weight of 470.

(cf.2): A product obtained by precondensing an epoxy resin with a resol type phenol resin.

(cf. 3): Chromium sesquioxide (Cr203), average particle size 0.4 mm, then coated on a temporary support film of polyethylene terephthalate with a diameter of 20 mm to a dry thickness of 5 mm. , hardened the surface using far infrared rays.

The wide medium sheet produced in this way was slit into 1 h/m pieces, and an amorphous linear polyester adhesive was used on the magnetic layer side to form a 0.75 m/m thick hard vinyl chloride resin plate. A magnetic card was made by attaching the material to the paper by heating and pressing and removing the temporary support. The saturation magnetization of the magnetic layer of this card is 2200 Gauss, the coercive force is -196oC, and the e is 13.
, 120 e at -8000 and 300 e at 20°C.

This power cord is suitable for magnetic recording at low temperatures, and is difficult to erase or record at room temperature. This card is 60oC
When stored in an environment of 90% RH for one week, the saturation magnetization was 2090 Gauss.

The reduction rate was 9.5%. Comparative Example 1 A magnetic card was produced in the same manner as in Example 1 except that the chromium treatment in Example 1 was not carried out (butyl acetate 11 base was further added to the binder).

The saturation magnetization of the magnetic layer of this card was 2010 Gauss. When this card was kept in an environment of 6000 RH and 90% RH for one week, the saturation magnetization was 1150 Gauss. The reduction rate is 43%. Example 2 After mixing finely ground Mn and Bj in fugas and press-molding, the mixture was sealed in vacuum and reacted at 320 qo for 10 days to produce MnBi, which was ground in acetone with a ball mill to obtain an average particle size of 0. The magnetic particles had a diameter of .55 m.

The slurry was centrifuged, and 205 parts of the obtained MnBi acetone-containing cake (containing 10 parts of MnBi powder) was added to the next chromium treatment solution, and vigorously heated for 10 minutes while applying ultrasonic waves (2 days). I worshiped the hawk.

The temperature of the treatment liquid is 20q○. {Foot fin, saddle poison... After sanding 120 parts of sand on 3 sides, the magnetic powder was centrifuged.

Subsequently, 200 parts of distilled water was gradually poured onto the cake in the rotating centrifuge to wash the cake. All of the above operations were performed in an N2 stream. The cake was then placed in a batch dryer and dried while being kept at 105 qo while being evacuated.

After drying for 8 hours, the magnetic powder was added to the next binder-containing composition without exposing it to air.

Each amount is shown per 100 parts of M-vortex powder. MnBi
After adding the flour, the composition was ball milled for 2 hours. The obtained coating solution was applied onto a polyimide base having a thickness of 23 mm and dried at 180 mm.

This coated object was cut into a tape shape to prepare a magnetic recording medium.
The dry thickness was 5 mm. The temperature characteristics of the coercive force of the magnetic recording medium thus manufactured were as shown in Table 1 below.

Table 1 The saturation magnetization of this magnetic recording medium is 2170 Gauss, 6
The saturation magnetization when stored for one week at 0qo and 90% RH was 2040 Gauss.

The reduction rate is 9%. Comparative Example 2 A magnetic recording medium was produced in the same manner as in Example 2 except that the chromium treatment in Example 2 was not performed.

The saturation magnetization of this magnetic layer was 1950 Gauss. When this magnetic layer was stored for one week in an environment of 6000 °C and 90% RH, the saturation magnetization was 1220 Gauss. The reduction rate is 38%. As is clear from the above, the magnetic recording material of the present invention has an extremely large coercive force near room temperature;
It has a coercive force that makes recording or erasing easy at low temperatures. It is also characterized by excellent weather resistance. In addition, when the magnetic materials of Examples 1 and 2 were dissolved in hydrochloric acid and examined by atomic absorption spectroscopy, it was found that the magnetic materials contained 2.8% and 3.9%, respectively.
It contained chromium.

Claims (1)

[Claims] 1. A magnetic recording material having a magnetic layer consisting of magnetic alloy particles mainly composed of Mn and Bi and a binder on a non-magnetic support, characterized in that the magnetic alloy particles have a Cr-containing surface layer. magnetic recording medium.