JP2002342913A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having a high signal-to-noise ratio and low surface electric resistance by using very fine magnetic powder. SOLUTION: An upper magnetic layer 105 which is a magnetic recording layer formed on a nonmagnetic base 101 of the magnetic recording medium is formed by dispersing magnetic powder 111 deposited or mixed with carbon 109 on or with hexagonal system ferrite particles 107 into an organic binder 113. The carbon content in the magnetic powder 111 is specified to 3 to 30 wt.% and the squareness ratio SQ of the upper magnetic layer 105 is controlled to >=0.80, the peak value of δM to -0.1 to 0.5, the surface electric resistance ER to 9×10<13> Ω/sq and the coercive force to 110 to 230 kA/m, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium using hexagonal ferrite powder.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is provided with a magnetic layer in which a magnetic powder is dispersed in an organic binder on a non-magnetic support, and the magnetic layer is formed by applying a magnetic paint. In such a magnetic recording medium, the miniaturization and dispersibility of the magnetic powder are required with the increase in the recording density. That point,
Hexagonal ferrite typified by hexagonal barium ferrite can be miniaturized in its manufacturing method and is a promising material as a magnetic powder for future high recording density magnetic recording media.

[0003]

By the way, when a magnetic recording medium is oriented at the time of application of a magnetic paint, magnetic particles are arranged in a fixed direction, and a squareness ratio (SQ) is increased, the S / N is generally increased. improves. However, hexagonal ferrite has a small particle size and its shape, so it stacks (agglomerates) during orientation during magnetic recording medium fabrication, and although the squareness ratio increases, the dispersibility deteriorates and the magnetic properties between the particles decrease. S / N is degraded due to static interaction. Therefore, if the orientation magnetic field is reduced or orientation is suppressed without orientation so that hexagonal system ferrite is not stacked, stacking is suppressed, but the squareness ratio is reduced and S / N is deteriorated.

Further, with the increase in recording density, a magnetoresistive read head (hereinafter referred to as MR head) capable of obtaining a sufficient output even on a magnetic recording medium having a low saturation magnetization.
Has been introduced. The MR head includes an electric resistance effect element (hereinafter, referred to as an MR element) exhibiting an electric resistance effect.
An electrode for applying a current to the MR element is provided, which detects a signal magnetic field generated from the magnetic recording medium as a change in resistance of the MR element and outputs the signal as a reproduction signal, and is easily damaged by static electricity. Therefore, in a magnetic recording / reproducing system using an MR head, it is required to reduce the surface electric resistance of the magnetic recording medium.

[0005] The present invention has been made in view of the above-mentioned problems of the prior art.
It is an object of the present invention to provide a magnetic recording medium in which dispersibility and S / N are sufficiently improved and surface electric resistance is reduced.

[0006]

Means for Solving the Problems In order to achieve the above object, the invention of claim 1 provides a magnetic recording medium having a magnetic layer containing a magnetic powder formed on a nonmagnetic support. The magnetic powder contains 3% by weight or more and 30% by weight or less of carbon in addition to the hexagonal ferrite powder, the squareness ratio is 0.80 or more, and the peak value of δM is -0.1 or more. , 0.5 or less, and the coercive force is 110 k
It is not less than A / m and not more than 230 kA / m.

In the present invention, the hexagonal ferrite powder, which is a ferromagnetic substance, contains carbon, which is a non-magnetic component, to increase the distance between adjacent particles of the hexagonal ferrite powder. By preventing powder stacking and orienting sufficiently in this state so that the squareness ratio is 0.80 or more, it is possible to improve the squareness ratio while reducing the magnetic interaction between the particles. , S / N can be improved.

In this case, the peak value of δM is used as an index of the magnetic interaction between the particles, and the content of carbon and the degree of orientation are controlled based on the peak value of δM, so that the S / N ratio is improved. Improvement is possible. The peak value of δM is related to the magnitude of the magnetic interaction between the particles, and is most preferably 0, and stacking of the magnetic powder occurs as the value shifts to −1 or 1. From the remanence curve plotting the remanent magnetization with respect to the applied external magnetic field, δM is obtained from the AC remanence from the AC degaussing state and the DC remanence from the DC degaussing state.
The difference from the remanence is defined and calculated as follows.

ΔM = ｛Id (H) + 2Ir (H) −Ir
(∞)｝ / Ir (∞)

However, Id (H) is the residual magnetization when measured with DC degaussing, Ir (H) is the residual magnetization when measured with AC degaussing, and Ir (∞) is the value when the applied magnetic field is 10 kOe. Remanent magnetization.

Here, AC demagnetization, DC
Demagnetize and measure δM in the longitudinal orientation direction. When the peak value of δM is smaller than −0.1, a magnetic interaction appears between particles vertically adjacent to the longitudinal orientation direction, and S / N
Deteriorates. When the peak value of δM is larger than 0.5, magnetic interaction appears between particles adjacent in parallel in the longitudinal orientation direction, and S / N is deteriorated.

In the present invention, by setting the carbon content in the magnetic powder to 3% by weight or more, stacking of the hexagonal ferrite powder can be prevented, and the surface electric resistance can be reduced to 9 × 10 5 It can be reduced to ¹³ Ω / sq or less, which can prevent electrostatic destruction of the MR head that reads a recording signal from the magnetic recording medium. Therefore, it is suitable as a recording medium for a magnetic recording system using the MR head. Used. If the carbon content in the magnetic powder is 30% by weight or more, the proportion of the non-magnetic component in the magnetic powder increases, and the saturation magnetization decreases, so that a sufficient output cannot be obtained. The carbon may be simply added and mixed together with the hexagonal ferrite powder at the time of preparing the coating material, or may be used by attaching it to the particle surface of the hexagonal ferrite powder before preparing the coating material.

Further, in the present invention, by setting the coercive force of the magnetic layer to be in the range of 110 to 230 kA / m, it becomes possible to appropriately perform the magnetization reversal at the time of recording.
N can be prevented from deteriorating.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a magnetic recording medium according to the present invention.
An upper magnetic layer 105 which is a magnetic recording layer is formed on a lower non-magnetic layer 103 via the lower magnetic layer 103. The upper magnetic layer 10
5, a ferromagnetic hexagonal ferrite 107
A magnetic powder 111 in which carbon 109 as a non-magnetic component is adhered or mixed is dispersed in an organic binder 113.

In the above configuration, the hexagonal ferrite 107 which is the main component of the magnetic powder 111 is typically a hexagonal barium ferrite, but includes strontium, lead, calcium, cobalt and the like.
In addition, S, Sc, Ti, V, Cr,
Cu, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hg, Pb, Bi, Ce,
It may contain atoms such as P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Zn,
Co-Ti, Co-Ti-Zr, Co-Ti-Zn, N
i-Ti-Zn, Nb-Zn-Co, Sb-Zn-C
Those to which elements such as o and Nb-Zn are added can be used. Some raw materials and production methods contain specific impurities.

The hexagonal ferrite powder preferably has a particle size of 10 to 80 nm in hexagonal plate diameter and a plate ratio (plate diameter / plate thickness) of 2 to 10. If the particle size is smaller than 10 nm in hexagonal plate diameter, superparamagnetism is obtained, stable magnetization cannot be maintained, and S / N is deteriorated. On the other hand, when the particle size is larger than 80 nm, when the magnetic recording layer is formed using the particle size, the surface smoothness of the coating film is impaired,
Noise increases. Also, it is not suitable for short wavelength recording. If the plate ratio is less than 2, the orientation deteriorates and the noise increases when coated after dispersion. If the plate ratio is greater than 10, the stacking is strong, the dispersibility deteriorates, and the S / N deteriorates. I do.

As a method for producing hexagonal ferrite, barium oxide, iron oxide, a metal oxide for substituting iron if necessary, and boron oxide or the like as a glass-forming substance are mixed so as to have a desired ferrite composition. Melting, quenching to form an amorphous body, and then reheating treatment, then washing and pulverizing to obtain a barium ferrite crystal powder, a glass crystallization method,
A barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, then is heated in a liquid phase at 100 ° C. or higher, and is washed, dried, and pulverized to obtain a barium ferrite crystal powder. The ferrite composition metal salt solution is neutralized with an alkali to remove by-products, then dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder. We do not choose manufacturing method.

In the magnetic powder 111, as the carbon 109 to be adhered to or mixed with the hexagonal ferrite 107, carbon black obtained by any production method can be used. For example, furnace black, thermal black, acetylene black, channel black, lamp black and the like can be used. Carbon black may be surface-treated with a dispersant or the like, grafted with a resin, or a part of the surface may be made into graphite. These carbon blacks can be used alone or in combination.

The magnetic powder 111 contains the carbon 109 in an amount of 3 to 30% by weight, preferably 5 to 30% by weight.
If the carbon content is less than 3% by weight, it is not possible to uniformly penetrate between the hexagonal ferrite particles, and the stacking of the hexagonal ferrite is insufficiently suppressed, and the S / N deteriorates due to magnetic interaction. I do. 1% by weight
In the following, the surface electric resistance of the upper magnetic layer 105 becomes large, and there is a possibility that the electrostatic breakdown of the MR head is caused. When the carbon content is more than 30% by weight, the saturation magnetization of the upper magnetic layer 105 becomes small, and the output is reduced.

Regarding the method of containing carbon, a method of preparing a magnetic recording medium by preparing a magnetic paint after depositing carbon on hexagonal ferrite, a method of adding carbon at the time of preparing a magnetic paint, or both of them can be used. Although it may be used in combination, a method of depositing carbon on hexagonal ferrite is preferred. A known method can be used as a method of applying carbon to the hexagonal ferrite. For example, a resin may be used as an adhesive, or carbon may be applied by a mechanochemical reaction. As a device for applying carbon by a mechanochemical reaction, a device capable of applying a shearing force to a powder layer is preferable, and in particular, a device capable of simultaneously performing shearing, spatula and compression is more preferable, for example, A wheel-type kneader, a ball-type kneader, a blade-type kneader, and a roll-type kneader can be used.

The magnetic recording medium manufactured by using the magnetic powder 111 has a squareness ratio (SQ) of 0.1 in the longitudinal orientation direction.
It is controlled to be 80 or more. When the squareness ratio is smaller than 0.80, the residual saturation magnetization becomes small, and the S / N deteriorates.

The magnetic recording medium according to the present embodiment has a δ
Control is performed so that the peak value of M falls within the range of -0.1 to 0.5. δM has a corresponding relationship with the magnetic interaction of the magnetic powder, and the peak value of δM can be used as an index of dispersibility or magnetic interaction. In the present embodiment, AC degaussing and DC degaussing are performed in the longitudinal orientation direction, and δM is measured in the longitudinal orientation direction. The peak value of δM is -0.1
If it is smaller, a magnetic interaction appears between the particles vertically adjacent to the longitudinal orientation direction, and the S / N deteriorates. Also,
When the peak value of δM is larger than 0.5, magnetic interaction appears between particles adjacent in parallel in the longitudinal orientation direction, and S / N is deteriorated.

The magnetic recording medium of the present embodiment is preferably adjusted so that the surface electric resistance is 9 × 10 ¹³ Ω / sq or less. Surface electric resistance is 9 × 10 ¹³ Ω / s
If it is larger than q, the MR head is likely to be broken by static electricity.

The magnetic recording medium of the present embodiment is preferably controlled so that the coercive force is in the range of 110 to 230 kA / m. When the coercive force is smaller than 110 kA / m, magnetization reversal easily occurs during recording, and S / N deteriorates. On the other hand, if the coercive force is greater than 230 kA / m, it becomes difficult to perform magnetization reversal during recording, and the S / N deteriorates.

In the magnetic recording medium of the present embodiment, as shown in FIG. 1, the magnetic recording layer mainly composed of the magnetic powder 111 and the organic binder 113 is provided on the non-magnetic support 101 as a lower layer. It has a structure formed with the non-magnetic layer 103 interposed therebetween, but the present invention is not limited to this. The magnetic layer may be a single layer of only the magnetic recording layer, or may have a lower magnetic layer. There is no particular limitation on the binder constituting the non-magnetic support or the magnetic coating film and other additives. Known pigments can be used for the magnetic layer other than the magnetic recording layer and the pigment of the non-magnetic layer.

As the organic binder, any of those used in ordinary coating type magnetic recording media can be used. As the thermoplastic resin, the glass transition temperature is -100 to 150
° C, preferably -25 to 100 ° C, and a number average molecular weight of 1,
000-200,000, preferably 10,000-1
00,000 and a degree of polymerization of about 50 to 100. Such examples include vinyl chloride, vinyl acetate,
Vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal,
There are polymers or copolymers containing vinyl ether or the like as a constituent unit, polyurethane resins, and various rubber resins.

The thermosetting resin or the reactive resin includes a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, and an epoxy-polyamide. Resins, a mixture of a polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like.

The above resins can be used alone or in combination. Preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer. A combination of at least one selected from coalescing and a polyurethane resin, or a combination of these with a polyisocyanate is exemplified.

As the polyurethane resin, polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane,
Known materials such as polycaprolactone polyurethane can be used, but the glass transition temperature is −50 to 150 ° C., preferably 0 to 100 ° C., the breaking elongation is 100 to 2000%, the breaking stress is 0.05 to 10 kg / mm ² , Yield point is 0.0
It is preferably in the range of 5 to 10 kg / mm ² .

Examples of the polyisocyanate include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and the like. Or a product of these isocyanates and polyalcohol, or a polyisocyanate formed by condensation of isocyanates. These polyisocyanates can be used alone or in combination of two or more by utilizing the difference in curing reactivity in each layer using a binder.

For all the binders shown here,
Required for better dispersibility and durability.
, -COOM, -SO_ThreeM, -OSO_ThreeM, -P = O
(OM) _Two, -OP = O (OM)_Two, -OH, -N
R_Two, -N⁺R_Three, Epoxy group, -SH, -CN (wherein,
M is a hydrogen atom or an alkali metal base, R is a hydrocarbon
Represents a group. At least one or more poles selected from
Use those having a reactive group introduced by copolymerization or addition reaction.
Is preferred. The amount of such polar groups is 10^-8-10
^-1Mol / g, preferably 10^-6-10^-2Mol / g
It is.

Specific examples of such an organic binder include VAGH, VYHH, manufactured by Union Carbide.
VMCH, VAGF, VAGD, VROH, VYES,
VYNC, VMCC, XYHL, XYSG, PKHH,
PKHJ, PKHC, PKFE, Nissin Chemical Industries MP
R-TA, MPR-TA5, MPR-TAL, MPR-
TSN, MPR-TMF, MPR-TS, MPR-T
M, MPR-TAO, 1000 W, DX8 manufactured by Denki Kagaku
0, DX81, DX82, DX83, 100FD, MR104, MR105, MR110, MR manufactured by Zeon Corporation
100, MR555, 400X-110A, Nipporan N2301, N2302, N23 manufactured by Nippon Polyurethane Co.
04, Pandex T-5105, T manufactured by Dainippon Ink and Chemicals, Inc.
-R3080, T-5201, Barnock D-400,
D-210-80, Chris Bon 6109, 7209, Toyobo Co. Byron UR8200, UR8300, UR8
700, RV530, RV280, Daiferamine 4020, 5020, 5100, 5300, 9 manufactured by Dainichi Seika
020,9022,7020, Mitsubishi Kasei MX500
4, Sanyo Kasei Co., Ltd. sampler SP-150, Asahi Kasei Corporation Saran F310, F210 and the like.

The organic binder used in the nonmagnetic layer and the magnetic layer of the magnetic recording medium of the present invention is in the range of 5 to 50% by weight, preferably 10 to 50% by weight based on the nonmagnetic powder or the magnetic powder.
It is used in the range of 30% by weight. The range is 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, and 2 to 20% by weight when using a polyisocyanate. preferable. However, for example, when corrosion of the magnetic head is caused by a small amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate.

If necessary, additives such as a lubricant, an abrasive, an antistatic agent and the like may be added to these organic binders. Conventionally known materials can be used for these additives, and the additives are not limited at all.

For example, abrasives such as α-alumina, β-alumina, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond having an α conversion of 90% or more,
Known materials having a Mohs hardness of 6 or more, such as silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Also,
A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains the same if the main component is 90% or more.

The particle size of these abrasives is 0.01
To 2 μm, more preferably 0.05 to 1.0 μm, and particularly preferably a narrow particle size distribution in order to enhance the electromagnetic conversion characteristics. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as needed, or to use a single abrasive to broaden the particle size distribution to have the same effect. Tap density is 0.3 ~
2g / cc, water content 0.1-5%, pH 2-11,
The specific surface area is preferably from 1 to 30 m ² / g. The shape of the abrasive may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a corner in a part thereof is preferable because of high abrasiveness.

As other additives, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten graphite difluoride, boron nitride, graphite fluoride, silicon oil, silicon with polar groups, fatty acid-modified silicon, fluorine-containing silicon, fluorine-containing alcohol, fluorine-containing ester,
Polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenylether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid , Aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having a unit number of 10 to 24 (even if they contain unsaturated bonds or are branched And alkali metal salts thereof (Li,
Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having a unit number of 12 to 22 (may contain an unsaturated bond or may be branched) , An alkoxy alcohol having a unit number of 12 to 22, a carbon number of 10 to
A monofatty acid ester, a difatty acid ester, or a trifatty acid ester consisting of 24 monobasic fatty acids (which may contain an unsaturated bond or may be branched);
Fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, fatty acid amines having 8 to 22 carbon atoms, and the like can be used.

As the material of the non-magnetic support 101, any of the materials used for ordinary coating type magnetic recording media can be used, and polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, and cellulose. Cellulose derivatives such as triacetate, cellulose diacetate and cellulose butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide and polyamide imide; light metals such as aluminum alloys and titanium alloys; and alumina glass And the like. When a rigid substrate such as an Al alloy or a glass plate is used for the non-magnetic support, an oxide film such as alumite treatment or a Ni-P film is formed on the substrate surface so that the surface is hardened. Is also good.

The thickness of the nonmagnetic support 101 in the magnetic recording medium is 2 to 100 μm, preferably 2 to 80 μm.
m. In particular, when the magnetic recording medium is a computer tape, it is 3.0 to 6.5 μm (preferably 3.0 μm).
-6.0 μm, more preferably 4.0-5.5 μm)
Are used in the thickness range.

Further, an undercoat layer for improving adhesion may be provided between the nonmagnetic support 101 and the nonmagnetic layer or the magnetic layer. A known undercoat layer is used, and its thickness is 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm.
m.

The magnetic recording medium of the present invention may be a double-sided magnetic layer disk-shaped medium in which magnetic layers are provided on both sides of a non-magnetic support, or may be provided on only one side. When a magnetic layer is provided on only one side, a back coat layer may be provided on the non-magnetic support surface opposite to the magnetic layer in order to obtain effects such as antistatic and curl correction. As this back coat layer, a known one can be used, and its thickness is
It is 0.1 to 4 μm, preferably 0.3 to 2.0 μm.

As is apparent from the above description, according to the present embodiment, carbon is contained in hexagonal ferrite powder having a small particle size, and the carbon content, the squareness ratio, the peak value of δM, By controlling the surface electric resistance and the coercive force respectively within predetermined ranges, the S / N is improved, and
A magnetic recording medium that can be reproduced with low noise by the R head can be obtained.

Therefore, the magnetic recording medium of the present embodiment is also suitable as a magnetic tape of a magnetic recording system using an MR reproducing head. As the MR reproducing head, M
A recording / reproducing apparatus is configured by using a shield type MR head in which an R element is sandwiched between shields and mounting the same on a rotating drum. By combining a magnetic recording system using an MR reproducing head with the magnetic recording medium of the present invention, an unprecedented high-density recording system can be constructed. An example of a helical scan magnetic recording system using an MR reproducing head will be described below.
This is effective in all magnetic recording systems using the R reproducing head.

The magnetic recording / reproducing apparatus of the helical scan magnetic recording system is a helical scan type magnetic recording / reproducing apparatus which performs recording / reproducing using a rotating drum, and uses an MR head as a reproducing magnetic head mounted on the rotating drum. I do.

FIGS. 2 and 3 show one configuration example of a rotary drum device mounted on the magnetic recording / reproducing apparatus. Note that FIG.
FIG. 3 is a perspective view schematically showing the rotary drum device 1, and FIG. 3 is a plan view schematically showing a magnetic tape feed mechanism 10 including the rotary drum device 1.

As shown in FIG. 2, the rotary drum device 1
A cylindrical fixed drum 2, a cylindrical rotary drum 3, a motor 4 for rotating the rotary drum 3, and a pair of inductive magnetic heads 5a, 5a mounted on the rotary drum 3;
b and a pair of MR heads 6 mounted on the rotating drum 3
a, 6b.

The fixed drum 2 is a drum that is held without rotating. On the side of this fixed drum 2,
A lead guide portion 8 is formed along the running direction of the magnetic tape 7. The magnetic tape 7 is attached to the lead guide portion 8.
Follow along. The rotating drum 3 is arranged so that the center axis of the fixed drum 2 coincides with that of the fixed drum 2.

The rotary drum 3 is a drum that is driven to rotate at a predetermined rotation speed by the motor 4 during recording and reproduction on the magnetic tape 7. The rotating drum 3 is formed in a cylindrical shape having substantially the same diameter as the fixed drum 2.
And the central axes are aligned. A pair of inductive magnetic heads 5a, 5b and a pair of MRs are provided on a side of the rotary drum 3 facing the fixed drum 2.
Heads 6a and 6b are mounted.

Inductive magnetic heads 5a, 5b
Is a recording magnetic head in which a pair of magnetic cores are joined via a magnetic gap and a coil is wound around the magnetic core, and is used when recording a signal on the magnetic tape 7. The inductive magnetic heads 5a and 5b are mounted on the rotating drum 3 so that the angle formed therebetween with respect to the center of the rotating drum 3 is 180 °, and their magnetic gaps protrude from the outer periphery of the rotating drum 3. Have been. The inductive magnetic heads 5a and 5b are set so that the azimuth angles are opposite to each other so that azimuth recording is performed on the magnetic tape 7.

On the other hand, the MR heads 6a and 6b are reproducing magnetic heads having an MR element as a magnetic sensing element for detecting a signal from the magnetic tape 7, and are used when reproducing a signal from the magnetic tape 7. . These MR heads 6a and 6b are mounted on the rotating drum 3 such that the angle formed therebetween with respect to the center of the rotating drum 3 is 180 °, and their magnetic gap portions protrude from the outer periphery of the rotating drum 3. I have. These MR heads 6a and 6b are set so that the azimuth angles are opposite to each other so that signals recorded azimuthally on the magnetic tape 7 can be reproduced.

Then, the magnetic recording / reproducing apparatus records a signal on the magnetic tape 7 and reproduces a signal from the magnetic tape 7 by sliding the magnetic tape 7 on the rotating drum device 1. That is, at the time of recording / reproduction, the magnetic tape 7
As shown in FIG. 3, the recording medium is sent from the supply reel 11 via guide rollers 12 and 13 so as to be wound around the rotary drum device 1, and recording and reproduction are performed by the rotary drum device 1. The magnetic tape 7 recorded and reproduced by the rotary drum device 1 is sent to a take-up roll 18 via guide rollers 14 and 15, a capstan 16 and a guide roller 17. That is, the magnetic tape 7 is fed at a predetermined tension and speed by a capstan 16 which is driven to rotate by a capstan motor 19,
Is wound up on the winding roll 18.

At this time, the rotary drum 3 is driven to rotate by the motor 4 as shown by an arrow A in FIG. On the other hand, the magnetic tape 7 is attached to the lead guide 8 of the fixed drum 2.
Along the fixed drum 2 and the rotating drum 3 so as to slide obliquely. That is, the magnetic tape 7
2 is fed along the tape running direction from the tape entrance side along the lead guide portion 8 so as to be in sliding contact with the fixed drum 2 and the rotating drum 3 as shown by the arrow B in FIG. As shown by arrow C, the tape is sent to the tape exit side.

Next, the internal structure of the rotary drum device 1 will be described with reference to FIG. As shown in FIG.
In the center of the fixed drum 2 and the rotating drum 3, a rotating shaft 21
Is inserted. The fixed drum 2 and the rotating drum 3
The rotating shaft 21 is made of a conductive material, these are electrically conductive, and the fixed drum 2 is grounded.

Further, two bearings 22 and 23 are provided inside the sleeve of the fixed drum 2, whereby the rotating shaft 21 is rotatably supported with respect to the fixed drum 2. That is, the rotating shaft 21 is
By 23, it is rotatably supported by the fixed drum 2. On the other hand, the rotary drum 3 has a flange 24 formed on the inner peripheral portion thereof.
1 is fixed to the upper end. Thereby, the rotating drum 3 is configured to rotate with the rotation of the rotating shaft 21.

In order to transmit signals between the fixed drum 2 and the rotating drum 3, a rotary transformer 2, which is a non-contact type signal transmission device, is provided inside the rotating drum device 1.
5 are arranged. The rotary transformer 25 has a stator core 26 attached to the fixed drum 2 and a rotor core 27 attached to the rotating drum 3.

The stator core 26 and the rotor core 27 are
A magnetic material such as ferrite is formed in an annular shape around the rotation shaft 21. The stator core 26 has a pair of signal transmission rings 26a, 26b corresponding to the pair of inductive magnetic heads 5a, 5b and a pair of signal transmission rings 2 corresponding to the pair of MR heads 6a, 6b.
6c and a power transmission ring 26d for supplying power required for driving the pair of MR heads 6a and 6b are arranged concentrically. Similarly, the rotor core 27 also has
A pair of signal transmission rings 27a and 27b corresponding to a pair of inductive magnetic heads 5a and 5b, and a pair of M
Signal transmission ring 27c corresponding to R heads 6a and 6b
And a power transmission ring 27d for supplying power required for driving the pair of MR heads 6a and 6b are arranged concentrically.

These rings 26a, 26b, 26c,
26d, 27a, 27b, 27c, and 27d are rotating shafts 2
1 and each of the rings 26a, 26b, 26c, 2
6d and each ring 27a, 27b, 27 of the rotor core 27
c and 27d are arranged to face each other.
The rotary transformer 25 is connected to the stator core 2
Signals and electric power are transmitted in a non-contact manner between the respective rings 26a, 26b, 26c, 26d of No. 6 and the respective rings 27a, 27b, 27c, 27d of the rotor core 27.

The rotary drum device 1 is provided with a motor 4 for rotating and rotating the rotary drum 3. This motor 4 has a rotor 28 as a rotating part and a stator 29 as a fixed part. The rotor 28 is attached to the lower end of the rotating shaft 21 and includes a driving magnet 30. On the other hand, the stator 29 is attached to the fixed drum 2 and has a driving coil 31. By supplying a current to the driving coil 31, the rotating shaft 21 attached to the rotor 28 is supplied.
Rotates, and accordingly, the rotating drum 3 fixed to the rotating shaft 21 is rotationally driven.

Next, recording and reproduction by the above-described rotary drum device 1 will be described with reference to FIG. 5, which shows a schematic circuit configuration of the rotary drum device 1 and its peripheral circuits.

When recording a signal on the magnetic tape 7 using the rotary drum device 1, first, an electric current is supplied to the drive coil 31 of the motor 4, whereby the rotary drum 3 is driven to rotate. Then, while the rotary drum 3 is rotating, a recording signal from the external circuit 40 is supplied to the recording amplifier 41 as shown in FIG.

The recording amplifier 41 amplifies the recording signal from the external circuit 40, and when the signal is recorded by one of the inductive magnetic heads 5a, the signal transmission of the stator core 26 corresponding to the inductive magnetic head 5a is performed. The recording signal is supplied to the inductive magnetic head 5b and the recording signal is supplied to the signal transmission ring 26b of the stator core 26 corresponding to the inductive magnetic head 5b at the timing when the signal is recorded by the other inductive magnetic head 5b. I do.

As described above, the pair of inductive magnetic heads 5a and 5b are arranged so that the angle formed between them with respect to the center of the rotary drum 3 is 180 °, as described above. Head 5a,
5b is recorded alternately with a phase difference of 180 °. That is, the recording amplifier 41 alternates the timing of supplying a recording signal to one inductive magnetic head 5a and the timing of supplying a recording signal to the other inductive magnetic head 5b with a phase difference of 180 °. Switch to.

The recording signal supplied to the signal transmission ring 26a of the stator core 26 corresponding to one inductive magnetic head 5a is transmitted to the signal transmission ring 27a of the rotor core 27 in a non-contact manner. And
The recording signal transmitted to the signal transmission ring 27a of the rotor core 27 is supplied to the inductive magnetic head 5a, and a signal is recorded on the magnetic tape 7 by the inductive magnetic head 5a.

Similarly, the recording signal supplied to the signal transmission ring 26b of the stator core 26 corresponding to the other inductive magnetic head 5b is transmitted to the signal transmission ring 27b of the rotor core 27 in a non-contact manner. And
The recording signal transmitted to the signal transmission ring 27b of the rotor core 27 is supplied to the inductive magnetic head 5b, and a signal is recorded on the magnetic tape 7 by the inductive magnetic head 5b.

When reproducing a signal from the magnetic tape 7 using the rotary drum device 1, first, a current is supplied to the drive coil 31 of the motor 4 so that the rotary drum 3
Is driven to rotate. Then, while the rotary drum 3 is rotating, a high-frequency current from the oscillator 42 is supplied to the power drive 43 as shown in FIG.

The high-frequency current from the oscillator 42 is converted into a predetermined alternating current by the power drive 43 and then supplied to the power transmission ring 26 d of the stator core 26. Then, the alternating current supplied to the power transmission ring 26d of the stator core 26 is transmitted to the power transmission ring 27d of the rotor core 27 in a non-contact manner. The AC current transmitted to the power transmission ring 27d of the rotor core 27 is rectified by the rectifier 44 to become a DC current, and is supplied to the regulator 45. The DC current is set to a predetermined voltage by the regulator 45.

The current set to a predetermined voltage by the regulator 45 is applied to the pair of MR heads 6a and 6b.
Is supplied as a sense current. A reproducing amplifier 46 for detecting signals from the MR heads 6a and 6b is connected to the pair of MR heads 6a and 6b, and the current from the regulator 45 is also supplied to the reproducing amplifier 46. You.

Here, each of the MR heads 6a and 6b includes an MR element whose resistance value changes according to the magnitude of an external magnetic field. The MR heads 6a and 6b are
The resistance value of the MR element changes due to the signal magnetic field from the sensor element, thereby causing a voltage change in the sense current.

Then, the reproducing amplifier 46 detects this voltage change and outputs a signal corresponding to the voltage change as a reproduced signal. The reproducing amplifier 46 outputs a signal detected by the MR head 6a at the time of reproducing a signal by one MR head 6a, and outputs a signal at the timing of reproducing a signal by the other MR head 6b. The reproduced signal detected by the MR head 6b is output.

Here, the pair of MR heads 6a and 6b
As described above, the MR heads 6a and 6b are alternately reproduced with a phase difference of 180 ° since they are arranged so that the angle between them with respect to the center of the rotary drum 3 is 180 °. Will be. That is, the reproduction amplifier 46 alternately switches the timing of outputting the reproduction signal from one MR head 6a and the timing of outputting the reproduction signal from the other MR head 6b with a phase difference of 180 °. .

The reproduction signal from the reproduction amplifier 46 is supplied to the signal transmission ring 27c of the rotor core 27, and the reproduction signal is transmitted to the signal transmission ring 26c of the stator core 26 without contact. Stator core 26
The reproduction signal transmitted to the signal transmission ring 26c of FIG.
Supplied to Then, the reproduction signal is subjected to predetermined correction processing by the correction circuit 48, and then output to the external circuit 40.

In the case of the circuit configuration shown in FIG. 5, a pair of inductive magnetic heads 5a, 5b,
The pair of MR heads 6a and 6b, the rectifier 44, the regulator 45, and the reproducing amplifier 46 are mounted on the rotating drum 3 and rotate together with the rotating drum 3. On the other hand, the recording amplifier 41, the oscillator 42, the power drive 43, the reproducing amplifier 47, and the correction circuit 48 are arranged on a fixed portion of the rotary drum device 1, or
And an external circuit configured separately.

Next, the MR mounted on the rotary drum 3
The heads 6a and 6b will be described in detail with reference to FIG. Note that the MR head 6a and the MR head 6b are set so that the azimuth angles are opposite to each other.
It has the same configuration. Therefore, in the following description, these MR heads 6a and 6b are collectively referred to as the MR head 6.

The MR head 6 is mounted on the rotating drum 3,
This is a read-only magnetic head that detects a signal from the magnetic tape 7 using the magnetoresistance effect by the helical scan method. Generally, MR heads are more inductive than magnetic heads that perform recording and reproduction using electromagnetic induction.
Because of its high sensitivity and high reproduction output, it is suitable for high-density recording. Therefore, by using the MR head 6 as the reproducing magnetic head, higher density recording can be achieved.

As shown in FIG. 6, the MR head 6 has a pair of magnetic shields 51 and 52 made of a soft magnetic material such as Ni—Zn polycrystalline ferrite, and a pair of magnetic shields 51 with an insulator 53 interposed therebetween. A substantially rectangular MR element portion 54 sandwiched between the magnetic shields 51 and 52 is provided. In addition,
A pair of terminals is led out from both ends of the MR element section 54, and a sense current can be supplied to the MR element section 54 through these terminals.

The MR element section 54 includes an MR element having a magnetoresistive effect and a SAL (Soft Adjustable).
ayer) film and an insulator film disposed between the MR element and the SAL film. The MR element is made of a soft magnetic material, such as Ni-Fe, whose resistance changes according to the magnitude of an external magnetic field due to the anisotropic magnetoresistance effect (AMR). The SAL film is for applying a bias magnetic field to the MR element by a so-called SAL bias method, and is made of a magnetic material having a low coercive force and a high magnetic permeability such as permalloy. The insulator film insulates between the MR element and the SAL film and prevents electronic shunt loss.
And the like.

The MR element portion 54 is formed in a substantially rectangular shape, and a pair of magnetic shields 51 and 52 is provided so that one side surface is exposed to the magnetic tape sliding surface 55.
3. More specifically, the MR element 54 has a pair of magnetic shields such that the short axis direction is substantially perpendicular to the magnetic tape sliding surface 55 and the long axis direction is substantially perpendicular to the magnetic tape sliding direction. It is sandwiched between insulators 51 and 52 via an insulator 53.

The magnetic tape sliding surface 55 of the MR head 6
Is cylindrically polished along the sliding direction of the magnetic tape 7 so that one side surface of the MR element 54 is exposed on the sliding surface 55 of the magnetic tape. Polished along the orthogonal direction. Thus, the MR head 6 is configured such that the MR element portion 54 or a portion near the MR element portion protrudes the most, so that the
The contact characteristics of the element portion 54 to the magnetic tape 7 can be improved.

When reproducing a signal from the magnetic tape 7 using the MR head 6 as described above, the magnetic tape 7 is slid on the MR element 54 as shown in FIG.
Note that the arrows in FIG. 7 schematically show how the magnetic tape 7 is magnetized.

Then, with the magnetic tape 7 slid on the MR element section 54, the MR element section 5 is connected via the terminals 54a and 54b connected to both ends of the MR element section 54.
4 is supplied with a sense current, and a voltage change of the sense current is detected. Specifically, a predetermined voltage Vc is applied from a terminal 54a connected to one end of the MR element 54, and a terminal 54b connected to the other end of the MR element 54 is
It is connected to the rotating drum 3. Here, the rotating drum 3 is electrically connected to the fixed drum 2 via the rotating shaft 21, and the fixed drum 2 is grounded. Therefore, one terminal 54b connected to the MR element 54 is
The rotating drum 3, the rotating shaft 21 and the fixed drum 2 are grounded.

Then, when a sense current is supplied to the MR element 54 while the magnetic tape 7 is slid, the M formed on the MR element 54 in response to the magnetic field from the magnetic tape 7.
The resistance value of the R element changes, and as a result, a voltage change occurs in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic tape 7 is detected, and the signal recorded on the magnetic tape 7 is reproduced.

In the MR head 6 to be used, the MR head
The MR element formed in the element section 54 may be any element that exhibits a magnetoresistance effect. For example, a so-called giant magnetoresistance effect is obtained by stacking a plurality of thin films so as to obtain a greater magnetoresistance effect. An element (GMR element) can also be used. The method of applying a magnetic field to the MR element may not be the SAL bias method, for example, a permanent magnet bias method, a shunt current bias method, a self-bias method, an exchange bias method, a barber pole method,
Various methods such as a split element method and a servo bias method can be applied. The giant magnetoresistance effect and various bias methods are described in detail in, for example, "Magnetoresistance Head Basics and Applications Translated by Kazuhiko Hayashi" by Maruzen Co., Ltd.

[0083]

The present invention will be described below in more detail with reference to examples. (Example 1) First, magnetic particles having a carbon content of 5% by weight were produced by applying carbon to the particle surfaces of hexagonal barium ferrite powder. The magnetic properties and powder properties of the magnetic powder are shown below. The magnetic properties were measured using a sample vibration magnetometer, and the specific surface area was measured using an automatic specific surface area meter (S
The measurement was performed using Himazu Corporation, Model 2200-02).

<Hexagonal barium ferrite particles> Particle size (hexagonal plate diameter): 30 nm Plate ratio (plate diameter / plate thickness): 5 Specific surface area: 57 m ² / g Saturation magnetization σs: 55 Am ² / kg Coercive force Hc : 170 kA / m <Carbon particles> Particle size: 20 nm Specific surface area (BET): 135 m ² / g

Next, an upper magnetic paint containing the above magnetic powder and a lower nonmagnetic paint containing the following pigment were prepared by mixing and kneading the following raw materials according to a usual production method. <Upper layer magnetic coating composition> Magnetic powder 100 parts by weight Binder resin (MR110 manufactured by Zeon Corporation) 20 parts by weight Abrasive (α-Al ₂ O ₃ , particle size 0.2 μm) 3 parts by weight Lubricant (myristic acid) 1 part by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexane 50 parts by weight <Lower layer nonmagnetic paint composition> Iron oxide powder (α-Fe ₂ O ₃ , major axis length 0.15 μm, specific surface area 55 m ² / g) 100 parts by weight Binder resin ( MR110 manufactured by Zeon Corporation) 20 parts by weight Lubricant (myristic acid) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexane 50 parts by weight

Next, polyethylene terephthalate (PE)
T) A lower non-magnetic paint was applied on the film, an upper magnetic paint was further applied, and then dried to form a lower non-magnetic layer and an upper magnetic layer, thereby producing a sample tape having a two-layer structure. The coating thickness is 0.3 μm for the upper magnetic layer and 1.5 μm for the lower non-magnetic layer.
An alignment magnetic field of 0 kA / m was applied. Thereafter, the sample tape was cut into a width of 8 mm to obtain a tape-shaped magnetic recording medium (hereinafter, simply referred to as a magnetic tape).

With respect to the magnetic tape produced as described above, the squareness ratio SQ, the peak value of δM, the surface electric resistance E
R, coercive force Hc, and electromagnetic conversion characteristics were measured. Regarding the electromagnetic conversion characteristics, after recording a signal at a recording wavelength of 0.5 μm using a modified 8 mm VTR, the shield type M
The reproduction output, noise level, and error rate were measured by the R head. The error rate indicates a symbol error rate. The MR head element used for reproduction is FeNi-AM
R (anisotropic magnetoresistance effect element), and the saturation magnetization is 80
0 emu / cc, thickness 40 nm, shield material is NiZ
n, the distance between the shields is 0.17 μm. The track width is 18 μm and the azimuth angle is 25 °. Table 1 shows the results of these measurements together with the carbon content of the magnetic powder.
And Table 2. Hereinafter, similarly, the following Example 2
Tables 1 and 2 show the measurement results of Comparative Examples 1 to 5 and Comparative Examples 1 to 5.

(Examples 2, 4, 11, 12, 13, 1
5) A magnetic tape was produced in the same manner as in Example 1 except that the carbon content was changed as shown in Table 1. (Examples 3, 9, 10) A magnetic tape was produced in the same manner as in Example 4, except that the coercive force of the hexagonal barium ferrite particles was changed. (Examples 5 and 6) A magnetic tape was produced in the same manner as in Example 4, except that the square magnetic ratio was changed as shown in Table 1 by changing the orientation magnetic field when producing the magnetic tape. (Example 7) A magnetic tape was produced in the same manner as in Example 4, except that the same amount of carbon was added and mixed at the time of producing the coating material without applying the carbon. (Example 8) Except that 10% by weight of carbon of 15% by weight of carbon content was applied to the surface of ferrite particles, and the remaining 5% by weight of carbon was added and mixed at the time of preparing a coating material, and was the same as Example 4. Similarly, a magnetic tape was produced. (Example 14) Compared with Example 13, the peak value of δM was changed by changing the plate ratio of the hexagonal barium ferrite powder, the method of dispersing the magnetic powder in the paint, and the orientation magnetic field after coating.
In the same manner as in Example 13, a magnetic tape was produced according to Example 13.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the carbon content was set to zero. Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the carbon content was 1% by weight. Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the carbon content was 35% by weight. Comparative Example 4 A magnetic tape was produced in the same manner as in Example 1, except that a hexagonal barium ferrite powder having a plate ratio of 10.5 was used. Comparative Example 5 A magnetic tape was produced in the same manner as in Example 1, except that a hexagonal barium ferrite powder having a coercive force Hc of 101 kA / m was used. Comparative Example 6 A magnetic tape was produced in the same manner as in Example 1, except that a hexagonal barium ferrite powder having a coercive force Hc of 231 kA / m was used.

[0090]

[Table 1]

[0091]

[Table 2]

In Tables 1 and 2, Examples 2, 4,
As is clear from 11, 12, and 13 and Comparative Examples 1 to 3, as the carbon content increases, the conductive component increases and the effect of reducing the surface electrical resistance increases, while the nonmagnetic component in the magnetic powder increases. However, when the carbon content is in the range of 3 to 30% by weight, preferably 5 to 30% by weight, the surface electric resistance of 9 × 10 ¹³ Ω / sq or less can be obtained. The required reproduction output can be secured, and the peak value of δM can be controlled in the range of −0.1 to 0.5,
S / N can be sufficiently improved by suppressing magnetic interaction between ferrite particles. In Comparative Example 1, since no carbon was present, the surface electric resistance was increased, the peak value of δM was increased, and the S / N was degraded. In Comparative Example 2, since the carbon content was small, it was difficult to uniformly infiltrate carbon between the ferrite particles, and the peak value of δM indicating the dispersion state of the ferrite particles was 0.5%.
Is getting bigger. In Comparative Example 3, since the content of carbon as a nonmagnetic component was large, a sufficient reproduction output could not be obtained, and the peak value of δM was smaller than -0.1, and the S / N was deteriorated. are doing.

As is clear from comparison between Examples 3, 4, 9 and 10, and comparison between Example 1 and Comparative Examples 4 and 5, the coercive force of the magnetic tape was 110 to 230 kA / m.
, The noise is prevented from increasing and the S / N
Degradation can be prevented. In Comparative Example 5 in which the coercive force is smaller than 110 kA / m, and in Comparative Example 6 in which the coercive force is larger than 230 kA / m, the noise increases and the S / N is deteriorated.

As is apparent from Examples 4 to 6,
By including carbon, even if the orientation magnetic field is strengthened to increase the squareness ratio, the magnetic interaction between ferrite particles does not increase as shown by the peak value of δM, and the S / N can be improved. it can.

Further, as is apparent from Examples 4, 7, and 8, the effect of improving the S / N was recognized irrespective of the method of containing carbon, but the effect of applying carbon was relatively improved. Is preferred.

As is clear from the comparison between Example 13 and Example 14 and the comparison between Example 1 and Comparative Example 4, δ
By controlling the dispersion state of the ferrite particles so that the peak value of M is -0.1 to 0.5, the magnetic interaction between the ferrite particles can be suppressed and the S / N can be improved. In Comparative Example 4, the peak value of δM was large, and the noise increased due to the magnetic interaction between the ferrite particles and the S / N was degraded.

[0097]

As described above, according to the first aspect of the present invention, carbon is contained in the hexagonal ferrite powder, and the carbon content, the squareness ratio, and the peak value of δM are controlled within predetermined ranges. Thereby, stacking of the ferrite powder can be prevented, and a magnetic recording medium having low surface electric resistance and excellent dispersibility and S / N characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one embodiment of a magnetic recording medium of the present invention.

FIG. 2 is a perspective view showing an example of a rotary drum device mounted on a helical scan type magnetic recording / reproducing apparatus.

FIG. 3 is a plan view schematically showing an example of a magnetic tape feeding mechanism including the rotary drum device of FIG. 2;

FIG. 4 is a sectional view showing an internal structure of the rotary drum device of FIG.

5 is a block diagram showing a circuit configuration of the rotary drum device of FIG. 2 and its peripheral circuits.

FIG. 6 is a perspective view illustrating a part of an MR head mounted on the rotary drum device of FIG.

FIG. 7 is a diagram schematically showing how a signal from a magnetic tape is reproduced using an MR head.

[Explanation of symbols]

101: Non-magnetic support, 103: Lower non-magnetic layer, 1
05: Upper magnetic layer, 107: hexagonal ferrite,
109 ... carbon, 111 ... magnetic powder, 113 ...
Organic binder

Claims (5)

[Claims] In a magnetic recording medium comprising a magnetic layer containing a magnetic powder formed on a non-magnetic support, the magnetic powder is added to the hexagonal ferrite powder in an amount of 3% by weight or more.
It contains 0% by weight or less of carbon and has a squareness ratio of 0.1%.
80 or more, the peak value of δM is -0.1 or more,
5 or less, and the coercive force is 110 kA / m or more, 230 k
A / m or less. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder is formed by depositing carbon on the particle surface of a hexagonal ferrite powder. 3. The magnetic recording medium according to claim 1, wherein the surface electric resistance is 9 × 10 ¹³ Ω / sq or less. 4. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is used in a magnetic recording system using a magnetoresistive read head. 5. The magnetic recording medium according to claim 4, wherein said magnetic recording system is a helical scan magnetic recording system.