JPH03124003A - Magnetic powder, manufacture thereof, magnetic recording medium and magnetic recording method - Google Patents

Abstract

PURPOSE:To acquire a magnetic recording medium of even frequency characteristics which is hard to erase after recorded using a magnetic powder having a good Curie point, high coercive force, high squareness ratio and stable properties by manufacturing and using a magnetic powder whose grain diameter and composition are specific. CONSTITUTION:Required materials are mixed, calcined, and ground by a vibrating mill, etc.; and burnt by an electric furnace, etc. Jet mill grinding is carried out to manufacture a magnetic powder of displacement M-type ferrite in a composition shown by an expression I, which is composed of a grain by 65% or more of an entire whose grain diameter is (0.5 to 5) X average grain diameter. Use of the magnetic powder of good Curie point, high coercive force, high squareness ratio and stable properties realizes a magnetic recording medium having even frequency characteristics which is hard to erase after recorded. In the expression, Me is one or more of Ba, Sr, Pb, Ca; and n, x, y: 4.5<=n<=6, x>=0, y>=0, x/3+y/4+z/6>=1/6, x/6+y/10+z/11<=1/6.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to magnetic powder, a method for producing the same, a magnetic recording medium using the same, and a magnetic recording method using the same.

<Prior art> A thermal transfer method is known as a contact transfer method for magnetic tape (for example, at the 1971 National Conference of the Institute of Electronics and Communication Engineers 59-7,
IEEE TRANSA(:Tl0N ONMAGNE
TICS, VOL, MAG-20, NO, 1,
JANUARY 1984P19-P23, etc.).

In the thermal transfer method, γ-F e 20 is used as the master tape.
Using a CrO□ tape or the like, the tape is heated to about 150° C. while running in contact with the CrO□ tape at high speed, and the signal is transferred by thermal transfer.

<Problems to be Solved by the Invention> However, in the conventional CrO* tape, the frequency characteristics of the transfer signal are not flat (it is necessary to apply emphasis when recording the master tape.

In addition, in the CrO□ tape, the coercive force H of Cr02 particles
Since a is as low as 0.4 to 0.7 kOe, it cannot be erased with a normal magnetic head, making it difficult to handle.

Therefore, the present inventors developed a magnetic powder having the composition shown by the following formula as a magnetic powder for magnetic recording media that has flat frequency characteristics and is difficult to erase after recording during thermomagnetic transfer and thermomagnetic recording. (Patent application No. 63-2816)
No. 79, Japanese Patent Application No. 1-144709) Formula MeO・n[Fez-X-y-zGaxcryA
ffizo3] (In the above formula, Me is Ba, Sr, Pb
and Ca.

Also, 4.5≦n≦6, X≧O, y≧012≧0, x/3 + y/4 + Z/6≧1/6
, x/6+y/l O+z/11≦1/6. ) This magnetic powder has a high Hc of 3 to 1 okoe and cannot be erased with a normal erasing head, making it convenient to handle.

And the Curie point Tc is 120 to 180°C,
Good thermomagnetic transfer and thermomagnetic recording can be performed.

Furthermore, the frequency characteristics during thermomagnetic transfer and thermomagnetic recording are extremely flat.

By the way, in order to manufacture such magnetic powder, it is generally preferable to do the following from the point of view of mass production.

In other words, the raw materials are first mixed, calcined, and then crushed.
Fire this.

Next, this is usually wet-pulverized using an attritor or the like, dried, and then crushed to obtain magnetic powder.

However, the magnetic powder obtained by such a method has a drawback that the particle size distribution is broad and the squareness ratio is particularly insufficient.

In addition, during wet pulverization, F from the media used for pulverization is
e and the like are mixed into the powder, resulting in an increase in Tc.

Furthermore, the characteristics of the magnetic powder vary due to variations in manufacturing conditions.

The objects of the present invention are to exhibit a good Curie point and high coercive force, a high squareness ratio, stable characteristics, flat frequency characteristics during thermomagnetic transfer and thermomagnetic recording, and a Magnetic powder realizes magnetic recording media that are difficult to erase,
A manufacturing method thereof, a magnetic recording medium using the magnetic powder,
The object of the present invention is to provide a magnetic recording method using the medium.

Means for Solving the Problems> Such objects are achieved by the present invention described in (1) to (8) below.

(1) It has a composition represented by the following formula, and is characterized in that the number of particles with a particle size of 0.5 to 1.5 J is 65% or more of the total, where J is the average particle size. magnetic powder.

Formula MeO・n[Fez-x-y-zGaxcryA
jzo3] (In the above formula, Me represents one or more of Ba, Sr, Pb and Ca.

Also, 4.5≦n≦6, X;ii:O, y≧0, Z≧0
, x / 3 + y / 4 + z / 6≧1/6
, x / 6 + y / 10 + z / 11≦
It is 1/6. ) (2) A magnetic powder having a composition represented by the following formula and characterized in that the Fe content on the particle surface is substantially equal to the Fe content inside the particle.

Formula MeO-n[Fez-++-y-zGaxcr,
ALO31 (In the above formula, Me represents one or more of Ba, Sr, Pb and Ca.

Also, 4.5≦n≦6, X≧0, y≧O1Z≧0, x/3 + y/4 +z/6≧1/6,
x / 6 + 3 / / 10 + z / 11≦
It is 1/6. ) (3) When the average particle size is ], the number of particles with a particle size of 0.5;
) Magnetic powder described in .

(4) The raw material powder is injected into the crushing chamber by a supply gas, and the supplied gas is injected as a high-speed airflow into the crushing chamber from a gas injection nozzle, and the raw material powder is crushed in the high-speed airflow inside the crushing chamber. . A method for producing magnetic powder, which comprises pulverizing it by forcibly colliding with a collision plate to obtain magnetic powder having a composition represented by the following formula.

Formula MeO-n[Fez-X-y-zGaxcryA
(In the above formula, Me represents one or more of Ba, Sr, Pb and Ca.

Also, 4.5≦n≦6, X≧0, y≧0, Z≧O1 x/3 + y/4 + z/6≧1/6
, x / 6 + y / 10 + z / 11≦
It is 1/6. ) (5) A method for producing magnetic powder, which comprises pulverizing raw material powder and then removing the surface by etching to obtain magnetic powder having a composition represented by the following formula.

Formula MeO・n[Fez-x-y-zGaxCryA
jzOx] (In the above formula, Me represents one or more of Ba%Sr, Pb, and Ca.

Also, 4.5≦n≦6, X≧o, y≧012≧01 x/3 + y/4 + z/6≧1/6
, x/6 + 3F/10 + z/11
≦1/6. (6) A magnetic recording medium comprising a magnetic layer containing the magnetic powder described in any one of (1) to (3) above in a binder.

(7) A magnetic recording method for performing thermomagnetic recording on the magnetic layer according to (6) above.

(8) A magnetic recording method in which thermomagnetic transfer is performed on the magnetic layer according to (6) above.

Effects> The magnetic powder of the present invention has a high Hc of 3 to 12 koe (it cannot be erased with a normal erasing head and is convenient in handling).

Further, it exhibits a stable Tc of 100 to 180°C, and can perform good thermomagnetic transfer and thermomagnetic recording.

At this time, the frequency characteristics during thermomagnetic transfer and thermomagnetic recording become extremely flat.

It also exhibits a high squareness ratio.

<Specific configuration> Hereinafter, a specific configuration of the present invention will be explained in detail.

The magnetic powder used in the present invention is a substituted M-type ferrite having a composition represented by the above formula.

In the above formula, Me represents Ba, Sr%Pb and Ca
When it is composed of two or more of these, the quantitative ratio is arbitrary, but it is particularly preferable that it contains one or more of Ba, Sr, and Pb as an essential component.

In this M type), the element substituting the elite is one or more of Ga%Cr and AI2.

The above relationships exist for the respective substitution amounts x, y, and z.

That is, x, y, and Z are x/3 + y/4 + z/6≧1/6, where x, y, Z≧O
And x/6+y/10+z/11≦1/6.

This is x/3 + y/4 + z/6 < 1
/ 6, the Curie point Tc is high, and x / 6 + y / 10 + z / 11 >
This is because at l/6, the saturation magnetization O3 decreases and Tc is too low, which is not practical.

In this case, the total 40a of Ga, Cr, Aρ
t% or less, In, Sc, Ti, Zn, Sn%Cr, T
It may be replaced with one or more of a, Sb, Bi, ■, Y, Mn, Co, Ni, etc.

Further, n is 4.5 to 6, particularly 5 to 6, but if it is a value other than this, σS will decrease or the Few 04 phase will precipitate.

The magnetic powder having such a composition is a hexagonal plate-like or crushed piece-like powder with a 60,000-piece structure.

When observing the SEM image of the powder, the average particle diameter J, which is the average (number average) of the maximum diameter of each particle under the field of view, is 0.3.
It is preferable that the number of houses is 3 to 3, particularly 0.5 to 2.

If J is less than 0.3 μs, the dispersibility will be poor and there will be a problem in the uniformity of the coating when applied, and if J is more than 3 scales, Hc will drop significantly.

On the other hand, as shown in FIG. 1, the particle size distribution of the powder is sharp.

The number of particles having a particle diameter in the range of 0.51 to 1.5 J is 65% or more, more preferably 80% or more of the total.

By creating such a sharp particle size distribution, the squareness ratio increases and the input/output characteristics are significantly improved.

The particle diameter (D large particle diameter) of each particle constituting the powder can be determined by image processing a SEM image using a known method.

Such a particle size distribution can be effectively achieved by jet milling as described below.

Note that the average grain size of each particle is 0.3 to
It is preferable to set it to about 3,0-.

Furthermore, it is preferable that the Fe content Cs on the particle surface of each particle constituting such magnetic powder is substantially the same as the Fe content C inside the particle.

These C8 and CL can be measured by Ouch analysis or ESCA while ion etching the powder, and when calculated as the initial Fe count Cs and the Fe count Ci after a predetermined time of ion etching, Cs
/Ci is preferably 0.9 to 1.1.

As mentioned above, in the usual method, Fe is mixed into the particle surface from the grinding media, etc., but as described later, the particle surface is etched after grinding, or the grinding is carried out using a jet mill. By doing so, it is possible to prevent or remove Fe from being mixed into the particle surface.

The magnetic powder of the present invention is produced as follows.

First, as a raw material, for example, 5rCO- AI2i 03 Crz Ox Gas 0sFe
Prepare a powder such as 20s BaCO5pbo with a particle size of about 0.3 to 2.0.

Next, this is blended using a ball mill attritor etc.
This is molded in air at 1000-1300℃, 2-4
Grill for hours.

Next, this is pulverized to a particle size of about 2 to 10 particles using a vibrating mill, a ball mill, an attritor, or the like.

Next, this is fired.

For firing, use an electric furnace or the like in air at a temperature of 1350 to 14
Bake at 50°C for about 2 to 4 hours.

Thereafter, the mixture is coarsely pulverized to about 2 to 5 particles using a vibration mill or the like, and then pulverized by a jet mill.

This jet mill pulverization is performed using a jet mill 10 as shown in FIG. 2, for example.

First, the hopper 2 of the jet mill pulverizer 10 is filled with coarse calcined powder 1 having an average particle size of 2 to 10%.

On the other hand, air is supplied from the gas supply port 3, and the fired powder 1 from the hopper 2 is supplied to the grinding chamber 6 at supersonic speed via the supply nozzle 4.

At this time, the flow rate of each supply gas is 500 to 1200 tn
/sec.

On the other hand, at a predetermined location of the ring-shaped crushing chamber 6,
A plurality of gas injection nozzles 5 that open in a direction slightly deviated from the tangential direction of the crushing chamber 6 are normally provided, and air is injected from the gas supply port 3 at supersonic speed.

With this configuration, the fired powder l supplied from the hopper 2 is pulverized by high-speed collision with each other or with the partition wall of the pulverizing chamber 6 in a supersonic air flow.

The thus finely pulverized fired powder l is classified by the high-speed swirling vortex flow and descends from the grinding chamber 6 into the cyclone 7.

Inside the cyclone 7, the fired powder 1 floats and swirls, and the extremely fine powder is discharged to the outside together with the inert gas through the discharge pipe 9. On the other hand, the fine powder is deposited at the bottom of the cyclone, and after stopping the supply of supersonic airflow, the cutting hopper 8 is opened.
Extracted as magnetic powder.

Note that in the jet mill crusher shown in FIG. 3, a collision plate 65 is provided in the crushing chamber 6.

After this, in the air at 300-1000℃ for 2-4 hours.
Annealing is performed for about an hour to remove distortion.

Thereafter, crushing is performed as necessary to obtain magnetic powder having the above-mentioned particle size distribution.

In the present invention, wet pulverization such as an attriter ball mill or a pearl mill may be used for pulverization after firing.

At this time, after pulverization, the surface is etched, followed by drying, annealing, and crushing.

For etching, an etchant such as hydrochloric acid is used, and the powder is immersed in this etchant at 20 to 40'C for about 10 to 30 minutes and stirred to mainly remove Fe mixed in from the media.

This etching is effective when wet pulverization is performed and is not necessary when jet mill pulverization is performed.

In addition, Hc of such powder is about 3 to 15 kOe, σ
S is about 5 to 15 emu/g, and σr is about 4 to 12 e
It is about mu/g, Tc is about 100 to 180°C,
The squareness ratio is 0.6 or more, preferably 0.7 or more, especially 0.
It is 7-0.9. The variation in these properties is extremely small.

The magnetic recording medium of the present invention has a magnetic layer containing such magnetic powder and a binder.

Dispersion in the binder improves flexibility and
Effects such as ease of handling are realized.

As the binder used, various known thermoplastic resins, thermosetting resins, radiation curable resins, reactive resins, etc. can be used.

The binder and the magnetic powder of the present invention have a weight ratio of 9:1 to 1:
9, particularly in a quantitative ratio of about 3:1 to 1:3.

Note that two or more types of binder and magnetic powder may be used,
Further, other magnetic powders may be used in combination as necessary.

In addition, the magnetic layer may contain known dispersants, abrasives, colorants,
A lubricant or the like may be contained.

The thickness of the magnetic layer may be approximately 0.5 to 30 pJn.

Note that a plurality of magnetic layers may be laminated.

As the substrate used, various known resins, metals, glasses, etc. can be used.

Note that various base layers, surface layers, intermediate layers, and back layers may be formed depending on the use of the medium.

There are the following methods for performing magnetic recording using such a magnetic recording medium.

The first is thermomagnetic recording.

At this time, the magnetic layer is heated to a temperature above the Curie point of the magnetic powder.
For example, normal recording may be performed by heating to about 120 to 180° C. using, for example, a laser beam.

The second one is thermomagnetic recording.

At this time, γ-Fe, which carries the mask signal, is
The signal may be transferred by heating to the above temperature while in contact with a magnetic layer such as zOx.

All of them exhibit a squareness ratio of 0.7 or more, have good input/output characteristics, and have extremely flat frequency characteristics of transferred or recorded signals.

<Example> Hereinafter, the present invention will be described in further detail by giving examples of the present invention.

Example 1 Raw materials were weighed, calcined in the air at 1300°C for 2 hours, and then ground to a particle size of 5 to 15-1, which was then molded and calcined in the air at 1420°C for 2 hours to obtain Sr0.・5.6 (Feazs(:r4.5zsAj+
, 5zs) were obtained.

This sintered body was coarsely ground to 5 pm or less using a vibration mill.

Next, this is passed through a jet mill pulverizer 1 shown in FIG.
It was pulverized at 0.

In this case, the nozzle outlet diameter is 10 mm, and the nozzle population diameter is 5 mm.
mm, and the flow rate of the supplied gas was 1000 m/sec.

Thereafter, it was annealed in air at 500° C. for 2 hours and crushed to obtain magnetic powder 1 of the present invention.

The SEM image of this magnetic powder was analyzed to calculate the maximum particle size of each particle, and the number average particle size J was calculated, which was 1.1-
Met.

In addition, 72% of the total number of particles were 0.5a-i,s
It was within the range of a.

Furthermore, while performing ion etching, Fe1l was counted by ESCA, and Cs/Ci was 0.
．． It was 95-1.05.

The properties of this magnetic powder 1 were as follows.

Tc 130°C1 Hc 11.0kOe, σS 6. Oemu/g.

Cr 5.1 emu/g.

The squareness ratio was 0.70.

Using this magnetic powder, the following composition was prepared.

Magnetic powder 120 parts by weight Carbon black 6 parts by weight Lecithin
2 parts by weight of nitrified cotton (H-1/2 seconds 15 parts by weight 70% chips of nitrified cotton in which 30% of isopropyl alcohol was replaced with 30% of VAGH, a salt-vinyl acetate copolymer manufactured by UCC) Methyl ethyl ketone, 50 parts by weight of methyl isobutyl ketone 50 Parts by Weight Among these compositions, after thoroughly dissolving the nitrified cotton chips, lecithin, methyl ethyl ketone, and methyl isobutyl ketone with a stirrer, these were placed in a ball mill together with magnetic powder and carbon black, and mixed for 3 hours (wetted). .

Next, a composition consisting of 15 parts by weight of polyurethane resin (Nisten 5701 manufactured by BF Gutdrich), 200 parts by weight of methyl ethyl ketone, 100 parts by weight of tetrahydrofuran, and 3 parts by weight of a lubricant (butyl myristate) was thoroughly mixed and dissolved. This was then put into the ball mill containing the previous composition, and mixed and dispersed again for 422 hours.

After dispersion, 5 parts by weight of an incyanate compound (Desmodur L manufactured by Bayer AG) capable of reacting with and crosslinking the functional groups, mainly hydroxyl groups, of the binder in the magnetic paint were added to the ball mill and mixed for 20 minutes.

The magnetic paint thus obtained was coated onto a 20 μm thick polyester film to make a magnetic tape, and after surface treatment, it was held at 80°C for 48 hours to advance the thermosetting reaction of the magnetic paint film. .

Furthermore, this was cut with a slitter.

The thickness of the magnetic layer was 10-.

The squareness ratio of this tape is 0.8, Hc10koe, B
r 2 , 7 emu/g.

Next, commercially available γ-Few O3 audio tape (TD
(manufactured by K Co., Ltd.) as the master tape, 60 Hz=
l OkHz signal was recorded.

This master tape and the above tape are connected at 2.5 m/s.
Thermomagnetic transfer was carried out while heating the film to 180° C. while running the film.

The output ratio between the output of the master tape and the output of the transfer tape is shown in Table 1 below. In this case, recording on the master tape is performed so that the output is flat in the range of 100Hz to 10kHz, and the OdB of the 1oOHz output of each transfer tape is
The output ratio of each frequency was calculated as follows.

Table 1 Invention (dB) Comparison (dB) 100Hz OO l kHz -1-1010k)lz
-1-5 For comparison, an example of CrO□ tape is also listed in Table 1.

In this case, the CrO□ magnetic powder used had an average particle size of 0.5-1
Hc 4000 e, a s 80 emu/g,
σ, 50 emu/g.

From the results shown in Table 1, the effects of the present invention are clear.

Comparative Example 1 In Example 1, attritor pulverization was performed instead of jet mill pulverization, and -pass drying was performed.

Hydrochloric acid was used as the etchant, and the surface was etched by immersing and stirring the magnetic powder in this at 25° C. for 30 minutes.

The characteristics of this magnetic powder 2 are as follows.

H1,3P 0,5 ] ~ 1.5; 748% Cs/Ci ≧ 1. I Tc 160℃Hc
7.5kOeσS
6. Oemu/g
σr4. 9em
u/g squareness ratio 0.51 Example 2 Etching was performed between the grinding and drying of the attritor in Comparative Example 1.

Drying was carried out at 80° C. in air.

The properties of this magnetic powder 3 were as follows.

H1,2m 015 ] ~ 1.5; 7 60% Cs/Ci 1 ±0.
05Tel 30℃
Hc 9.2kO
eσs 5. 9
emu/gσr 4
．． 8 emu/g squareness ratio 0.63 Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the magnetic powder 1 was changed to the following.

Magnetic powder 4 Sr0・5.8 (Fe5ieAlaitsOs) ■
1.8 胛0.5■～i, sg 71% Cs / Ci l±0.05Hc
12.3kOeas
4. lemu/gTc 160℃ Squareness ratio 0.73 Magnetic powder 5 SrO-5,6 (FeszaCrtzaOa)J
2.3 units 0.5zT ~1. FzT 73% Cs/C'i l±0.05Hc
8.6kOeas
5.2 emu/gTc 140°C Squareness ratio 0.72 Magnetic powder 6 SrO5,6 (FeazaGazzgCrzzeAj+
zaOs)a 1.5μ 0.5Go~1.5HT2% Cs/Ci l±0.05Hc
7.2kOeσs
6.2 emu/gTc 110° C. Squareness ratio 0.70 When each of the above magnetic powders was subjected to thermomagnetic transfer in the same manner as in Example 1, the same results as in Example 1 were obtained.

Example 4 Raw materials were weighed and sintered at 1450°C to obtain Ba0.5.
lll (Fea, 5zaGaazaCri, 57aO
After obtaining x), this was crushed in the same manner as in Example 1 to obtain magnetic powder 7 with Go = 1.3-.

The characteristics of this magnetic powder 7 were as follows.

J 1.4 units 0.5z
T ~1.51 71% Cs/Cil ±0.
05Hc 5
kOeO95.5emu/g Tc 120°C Squareness ratio 0.74 A medium was prepared using this magnetic powder 7 in the same manner as in Example 1,
When thermomagnetic transfer was performed, the same results as in Example 1 were obtained.

Example 5 The following magnetic masks 8 to 12 were produced in the same manner as in Example 3.

Magnetic powder 8 Ba0・5.8 ] 0.5■~1°Cs / Cia σ S Hc Square ratio Magnetic powder 9 Bad-5,8 (Fet 035a~1°Cs / Ci Hc σ S Hc Square ratio (Fe7zsGa3zaCrzzs04 ) 1, 2-70% 1 ± 0, 05 kOe 8, 5 emu/g 40°C 0, 74 5] 5zecr4.S/603) 1, 2- 5 71% 1 ± 0, 05 7.1 kOe 8, lemu/g 180°C 0,70 Magnetic powder 10 Ba0・5.8 ■ 0.5■～1.5 Cs / Ci Hc S Hc Square specific magnetic powder 11 Ba0・5.6 O,5H-1,5 Cs / Ci Hc σ S Hc Squareness ratio (Fe4/scrazaAg+t/a04) 1, 2- 1% 1 ± 0.05 koe 4, 1 emu/g O℃ 0, 73 CFe4ysAls7ao<) 7 3 1, 2p H72% 1 ± 0 , 05 1kOe 4, 1 emu/g 180°C 0, 73 Magnetic powder 12 BaO・5.6 (Fe5.azsGa+zaCr+z
++AL, 5zsO<)] 11.
1 unit, 5■~1.5'2r70% Cs/Ci 1±0.05Hc
7.2kOeas
7.2 emu/gT0 140°C Squareness ratio 0.75 For these magnetic powders 8 to 12, a medium was prepared in the same manner as in Example 1, and thermomagnetic transfer was performed, and results equivalent to those in Example 1 were obtained. .

Example 6 When magnetic recording was performed on the tapes of Examples 1 to 5 at 100 to 180°C, output with flat frequency characteristics could be obtained.

<Effects> According to the present invention, a magnetic layer having a high Hc and difficult to erase after recording can be replaced.

In addition, the squareness ratio is high (thermal magnetic transfer and thermomagnetic recording at temperatures of 100 to 180°C can be performed well;
Output with good frequency characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a photograph substituted for a drawing, and is a scanning electron micrograph showing the particle structure of the magnetic powder of the present invention. FIG. 2 and FIG. 3 are schematic vertical cross-sectional views each showing a jet mill pulverizer used in the present invention. Explanation of symbols 10... Jet mill pulverizer 1... Permanent magnet raw powder 2... Hopper 3... Gas introduction pipe 4... Supply nozzle 5... Gas injection nozzle 6... Grinding Chamber 65... Collision plate 7... Cyclone 8... Cutting hopper 9... Discharge pipe

Claims (8)

[Claims] (1) It has a composition represented by the following formula, and when the average particle size is represented by ■, the number of particles with a particle size of 0.5■ to 1.5■ is 65% or more of the total. magnetic powder. Formula MeO・n[Fe_2_−_x_−_y_−_zG
a_xCr_yAl_zO_3] {In the above formula, Me is
Represents one or more of Ba, Sr, Pb and Ca. Further, 4.5≦n≦6, x≧0, y≧0, z≧0, x/3+y/4+z/6≧1/6, x/6+y/10+z/11≦1/6. } (2) A magnetic powder having a composition represented by the following formula, and characterized in that the Fe content on the particle surface is substantially equal to the Fe content inside the particle. Formula MeO・n[Fe_2_−_x_−_y_−_zG
a_xCr_yAl_zO_3] {In the above formula, Me is
Represents one or more of Ba, Sr, Pb and Ca. Further, 4.5≦n≦6, x≧0, y≧0, z≧0, x/3+y/4+z/6≧1/6, x/6+y/10+z/11≦1/6. } (3) The magnetic powder according to claim 2, wherein the number of particles having a particle size of 0.5 to 1.5 is 65% or more of the total, where the average particle size is . (4) The raw material powder is injected into the crushing chamber by a supply gas, and the supplied gas is injected as a high-speed airflow into the crushing chamber from a gas injection nozzle, and the raw material powder is crushed in the high-speed airflow inside the crushing chamber. . A method for producing magnetic powder, which comprises pulverizing it by forcibly colliding with a collision plate to obtain magnetic powder having a composition represented by the following formula. Formula MeO・n[Fe_2_−_x_−_y_−_zG
a_xCr_yAl_zO_3] {In the above formula, Me is
Represents one or more of Ba, Sr, Pb and Ca. Further, 4.5≦n≦6, x≧0, y≧0, z≧0, x/3+y/4+z/6≧1/6, x/6+y/10+z/11≦1/6. } (5) A method for producing magnetic powder, which comprises pulverizing raw material powder and etching away the surface thereof to obtain magnetic powder having a composition represented by the following formula. Formula MeO・n[Fe_2_−_x_−_y_−_zG
a_xCr_yAl_zO_3] {In the above formula, Me is
Represents one or more of Ba, Sr, Pb and Ca. Further, 4.5≦n≦6, x≧0, y≧0, z≧0, x/3+y/4+z/6≧1/6, x/6+y/10+z/11≦1/6. } (6) A magnetic recording medium comprising a magnetic layer containing the magnetic powder according to any one of claims 1 to 3 in a binder. (7) A magnetic recording method for performing thermomagnetic recording on the magnetic layer according to claim 6. (8) A magnetic recording method in which thermomagnetic transfer is performed on the magnetic layer according to claim 6.