NL8502314A - PROCESS FOR THE PREPARATION OF MICROCRYSTALLINE BARIUM FRYRITE POWDER. - Google Patents

Description

. * - «853095 / vdV / cd

Title: Process for the preparation of microcrystalline barium ferrite powder.

The invention relates to a method of preparing a microcrystalline barium ferrite powder and more particularly to a method of preparing a microcrystalline hexogonal barium ferrite powder having a particle size ranging substantially from about 0.05 yam to about 0.5 yam and is suitable for use in magnetic recording.

Barium ferrite is a hexagonal crystal and is widely used as a magnetic material in various fields, for example, for the preparation of hard ferrites, rubber magnets and vertical magnetic recording medium. It is necessary that barium ferrite has suitable shapes and particle sizes in accordance with the particular applications, while the shape and particle size of the barium ferrite varies considerably depending on the preparation methods. For example, barium ferrite must be microcrystalline and exist in the form of well-defined hexagonal plates for use in vertical magnetic recording.

The hexagonal plate barium ferrite powder is normally prepared by mixing barium carbonate with iron oxide and with a flux such as barium chloride} and then the resulting mixture is calcined at about 1100 ° C or higher. This process produces barium ferrite powders which may, however, contain particles with a particle size of several 25 microns, but does not yield uniform and microcrystalline hesagonal powders with a particle size of no more than about 0.5 yam.

Another method is also known in which barium ions and iron (III) ions react with each other in an aqueous alkaline solution at a pH of not less than 8 at normal temperature under atmospheric pressure to form precipitates which are then calcined or baked at temperatures of about 900 ° C or higher to form barium ferrite powders. However, in this process, during the calcination, the precipitate partially sintered together to form large particles, so that it is difficult to perform according to this process.

iSi) 23U

to obtain microcrystalline barium ferrite powders containing mainly particles of not more than about 0.5 µm.

United States Patent 4,414,124 has proposed an improved process for preparing a microcrystalline hexagonal barium ferrite powder. This method consists of two steps. In the first step, an aqueous alkaline solution with a pH of 12 or higher containing barium ions and iron ions is heated in sufficient amounts to obtain barium ferrite to elevated temperature to precipitate a precursor of the barium ferrite. The pre-product has essentially the same chemical composition as the barium ferrite, but the pre-product has a low crystallinity because of its incomplete crystallization, so that the pre-product is not suitable for practical industrial applications. In particular, it is virtually impossible to use the precursor to produce a magnetic recording medium since the product has low coercive force (iHc) and magnetic saturation (is). In the second step of the process, the precursor is heated to temperatures of about 800 ° C or higher to fully crystallize the product into hexagonal plates. However, in this calcination step, the precursor particles sinter together and, as a result, the resulting barium ferrite powder contains large particles that are ill-defined hexagonal platelets. The magnetic recording medium obtained using such a barium ferrite has unsatisfactory magnetic properties and, more particularly, the magnetic recording medium has a small square-to-square ratio and therefore poor electrical output power.

The object of the present invention is therefore to provide a method for preparing a microcrystalline hexagonal barium ferrite powder.

More particularly, the invention aims to provide a method for preparing a microcrystalline, uniform barium ferrite powder in the form of well-defined hexagonal spots, which has a particle size of substantially from 0.05 µm to about 0.5 µm and is therefore suitable for use in the manufacture of a vertical magnetic recording medium with a high square ratio.

According to the invention, there is provided a method of preparing a microcrystalline hexagonal barium-5 ferrite powder of a general formula:

BaO. n / Fe1_mMin) 2 ° 3 // in which M is at least one substituent element selected from the group consisting of Co, Ti, Ni, Mn, Cu, Zn, In, Ge and Nb, m 0-0.2 and n 4.5 -6.0 is characterized by: forming an aqueous alkaline dispersion containing coprecipitates of hydroxides of barium ions, iron (III) ions, and optionally ions of the substituent element M, in a molar ratio in accordance with the general formula of the barium ferrite and having a pH of not less than about 12; heating the dispersion to temperatures of about 150-300 ° C to convert the coprecipitate into a precursor of the barium ferrite; calcining the precursor together with a water-soluble barium halide at temperatures of about 700-1000 ° C; and washing the calcined product with water to remove the barium halide from the resulting barium ferrite.

In the process of the invention, the precursor particles do not sinter together since the calcination is performed in the presence of the barium halide separating the precursor particles, so that the resulting barium ferrite is a microcrystalline powder in the form of well-defined hexagonal platelets with is an even particle size.

Other advantages of the invention will become apparent from the following description with reference to the accompanying drawings, in which: Figure 1 is an electron microscope photograph (60,000 x magnification) of a precursor obtained in the hydrothermal reaction of an aqueous alkaline dispersion according to the method of the invention; Figures 2 through 5 electron microscope photographs (60,000 magnification) of barium ferrite powders prepared by the method of the invention; and FIG. 6 is an electron microscope photograph (60,000 times magnification) of barium ferrite powder prepared by a known method.

According to the method of the invention, an aqueous alkaline dispersion is first prepared containing coprecipitates of hydroxides of barium ions, iron (III) ions and optionally ions of the substituent element H, in a molar ratio according to the general formula: 10. BaO. n / (Fei, mV 2 ° 3 // ', wherein M is at least one substituent element selected from the group consisting of Co, Ti, Ni, Mn, Cu, Zn, In, Ge and Nb, m 0-0.2 and n is 4.5-6.0 and with a pH of not less than about 12.

For illustrative purposes only, the dispersion can be prepared as follows. First, an aqueous solution is prepared containing barium ions, iron (III) ions and optionally ions of the substituent element M dissolved therein in a molar ratio in accordance with the above general formula and then the solution is added to an I under aqueous solution of a alkalinization of an aqueous dispersion. It is important that the aqueous solution and the dispersion contain barium ions, iron ions and optionally ions of the substituent element in a molar ratio in accordance with the above general formula to provide a well-defined hexagonal barium ferrite. It is difficult to obtain such a well-defined crystalline barium ferrite powder with improved magnetic properties when the molar ratio is outside the indicated limits. The substituent element M serves to reduce the coercive force of the obtained barium ferrite powder so that it is suitable for special applications of the powder, as will be described later. In the preparation of the alkaline dispersion, the alkali is usually used in excess of the ions in the solution to form coprecipitates of the hydroxides of the ions almost quantitatively.

The aqueous solution can be prepared by dissolving water-soluble compounds of the ions in water.

8502 3 1 4 -5-

The water-soluble compound of barium, iron (III) and the suitable substituent element contains, for example, nitrates such as barium nitrate, ferric nitrate, cobalt nitrate, titanium nitrate, nickel nitrate, manganese nitrate, cupric nitrate, zinc nitrate, indium nitrate, germanium nitrate and niobium nitrate barium perchlorate, ferric perchlorate, cobalt perchlorate, titanium perchlorate, nickel perchlorate, manganese perchlorate, copper perchlorate, zinc perchlorate and indium perchlorate; chlorates such as barium chlorate, ferric chlorate, cobalt chlorate, nickel chlorate, cuprous chlorate and zinc chlorate.

Chlorides such as barium chloride, ferric chloride, cobalt chloride, titanium chloride, nickel chloride, cupric chloride, manganese chloride, zinc chloride and indium chloride? fluorides such as ferric fluoride, cobalt fluoride, titanium fluoride, cupric fluoride, germanium fluoride and niobium fluoride acetates such as barium acetate, ferric acetate, cobalt acetate, nickel acetate, manganese acetate and zinc acetate; and sulfates such as cobalt (II) sulfate, titanium sulfate, nickel sulfate, manganese sulfate, zinc sulfate and indium sulfate.

The aqueous dispersion must have a pH of not less than 12 to obtain microcrystalline barium ferrite powder with a particle size of substantially no more than about 0.5 µm. Preferably, the dispersion has a pH of not less than 13. The alkali suitable for preparing the dispersion is preferably a strong alkali such as sodium hydroxide, potassium hydroxide or lithium hydroxide.

The dispersion is then subjected to a hydro-thermal reaction in which the dispersion is heated to temperatures of about 150 to about 300 ° C in a sealed reaction vessel, for example, an autoclave. The reaction time is not limited, but usually ranges from a few tens of minutes to several hours.

The hydrothermal reaction of the alkaline dispersion converts the coprecipitates of the ions into particles of the precursor of the barium ferrite of the chemical composition as defined in the general formula. As shown in Fig. 1, the precursor particle is almost a hexagonal crystal, but the crystallization is not yet complete, so that it has too low a coercive force and magnetic saturation rr ί "*» *., ® ....... I. "4 * -6- property when used in the magnetic recording media.

According to the method of the invention, the particles of the precursor are calcined or baked in the presence of a water-soluble barium halide. The barium halide 5 prevents sintering of the particles during the complete crystallization of the precursor. In other words, the barium halide separates the particles of the precursor and dilutes the particles so that the precursor particles do not sinter together. As a result, the individual particles of the precursor can crystallize completely independently of the other particles to form a microcrystalline, well-defined hexagonal platelet, powder which is also uniform in particle size as shown in Figures 2 through 5.

The precursor is mixed with the water-soluble barium halide in amounts of not less than about 30 parts by weight to 100 parts by weight of the barium ferrite precursor. Use of barium halide in amounts of less than 30 parts by weight to 100 parts by weight of the precursor is insufficient to prevent sintering of the precursor during the calcination. On the other hand, as already mentioned above, since the barium halide is removed from the calcined product, the barium halide can be used in great excess. However, using such a large excess of barium halide, it takes a long time to remove it from the calcined product, while no special advantages can be expected. Consequently, the amounts of barium halide used are up to about 200 parts by weight relative to 100 parts by weight of the precursor, and preferably from about 50 parts by weight to about 150 parts by weight, relative to 100 parts by weight of the precursor.

Usually, the precursor is mixed wet with the barium halide, dried and granulated or powdered and the mixture is heated in an electric oven, however, the method of mixing and calcining is not limited to this. The useful water-soluble barium halide includes barium chloride, barium iodide and barium fluoride, with barium chloride being preferred.

8502 3 1 4

♦ Q

-7-

The calcination temperature is preferably about 700 ° C to about 1000 ° C. When the calcination temperature is less than about 700 ° C, the crystallization of the precursor is insufficient to obtain a barium ferrite powder which has unsatisfactory mechanical properties, in particular, low magnetic saturation, while at calcination temperatures above 100 ° C C partially sintering the particles of the precursor and the resulting barium ferrite powder may contain large particles having a size greater than about 0.5 µm.

Calcination of the precursor according to the method of the invention, as described above, prevents sintering of the particles of the precursor during the complete crystallization of the product into hexagonal platelets and consequently the barium ferrite powder can be obtained in microcrystalline, well-defined hexagonal form with a uniform particle size of substantially from about 0.05 µm to about 0.5 µ111. The barium ferrite powder is therefore much better than the known barium ferrite powder in the square ratio which is one of the most important magnetic properties.

The barium ferrite powder according to the invention is therefore particularly suitable for the production of vertical magnetic recording media.

Magnetic recording normally relies on magnetization according to the longitudinal direction of the plane of the recording medium. As a result, a magnetic powder used therein as the magnetic recording material has easy axes of magnetization along the longitudinal direction of the plane of the recording medium and acicular. maggemite powder, acicular magnetite powder or these powders with a second metal incorporated therein, such as Co, are used as the magnetic powder. However, since the demagnetization field in the recording medium increases as the recording density is increased, the known recording system has a limitation in the recording density.

The vertical magnetic recording is therefore now in a strong development phase, using magnetization in a direction perpendicular to 85 02 3 14 9 '9 -8- the plane of the magnetic recording medium. Since the demagnetization in this recording medium becomes smaller as the recording density increases, the recording density can be considerably increased.

The magnetic powder used in the vertical recording must have convenient axes of magnetization perpendicular to the plane of the recording medium, and barium ferrite powder in the form of microcrystalline hexagonal plates can be used effectively for this purpose.

10 A well-known barium ferrite, BaO. 6Fe2C> 2, a compound wherein m in the above general formula is m, usually has a coercive force (iHc) of about 3000 to about 6000 Oersted. This value of the coercive force is too high for use in normal vertical magnetic recording, but the partial replacement of iron (III) ions with one or more of the above substituent element M reduces the coercive force of the resulting barium ferrite. coercive force does not exceed about 2000 Oersted. This value of the coercive force is suitable for the head of normal magnetic recording devices. As mentioned above, the substituent element M is at least one element selected from the group consisting of Co, Ti, Ni, Cu, Zn, In, Ge and Nb. Preferably Co is chosen as the substituent element M alone or in combination with other metals.

Example 1.

(1) Preparation of barium ferrite and its properties.

3467 ml of a 3.0 mol / 1 aqueous ferric chloride solution, 1100 ml of a 1.0 mol / 1 aqueous barium chloride solution, 800 ml of a 1.0 mol / 1 aqueous solution of cobalt chloride and 800 ml of a 1.0 mol / l aqueous solution of titanium tetrachloride were mixed together and the resulting solution was added to 5093 ml of a 15 mol / l aqueous sodium hydroxide solution at 15 to 20 ° C to obtain an aqueous dispersion with a pH of 14 containing coprecipitates of hydroxides of Fe, Ba, Co and Ti.

The dispersion was placed in an autoclave and heated at 250 ° C for 4 hours to obtain precipitates of the precursor of barium ferrite of the formula BaO. 5.45 (Fe 2, 40 908 Ti0, 147 and CO 0.147, 3.3). The pre-product was washed with 8502314 water -9 until the pH of the wash water was not more than 8 and dried. Pig. 1 is an electron microscope photograph (60,000 times magnification) of the precursor.

The particulate precursor was mixed wet with 5 barium chloride in varying amounts and water using a kneader and the resulting mixture granulated into spherical granules about 3 mm in size and dried. The granulate was then calcined in an electric oven at a predetermined temperature for 3 hours, finely ground, and then wet-ground to powder with a land grinder. The finely divided powder was then washed with water to remove barium chloride, filtered and dried to obtain microcrystalline barium ferrite powder. The properties of the barium ferrite powder thus obtained are shown in the table.

Figures 2, 3, 4 and 5 show electron microscope photographs of the barium ferrite products prepared according to tests 3, 4, 6 and 8 according to this example. From these electron microscope photos, it can be clearly seen that the barium ferrite of the invention consists of well-defined hexagonal platelets which have a particle size from about 0.05 µm to about 0.3 µm.

The coercive force (iHc) and magnetic saturation (Sa) of the barium ferrite measured with a vibration magnetometer as well as the specific surface area determined according to the BET method are also shown in the table.

(2) Manufacture of magnetic tape and its magnetic recording properties.

78 parts by weight of the barium fer powder obtained above were mixed with 17 parts by weight of poly (vinyl) chloride-vinyl acetate (copolymer as binder), 4 parts by weight of dioctyl-phthalate as plasticizer, 1 part by weight of lecithin as dispersant 120 parts by weight of methyl ethyl ketone and 120 parts by weight of tolu-35 both as solvents, and the resulting mixture was kneaded in a sand grinder to form a magnetic paint. The magnetic paint was then coated on a polyethylene terephthalate base film and dried under a 4 KG magnetic field perpendicular to the plane 6322 314-10- of the base film to form a magnetic recording tape with a vertical anisotropic magnetic orientation.

The magnetic properties of the magnetic tape were measured with a vibration magnetometer. The coercive force (iHc) and square ratio are shown in the table. Example 2.

3397 ml of a 3.0 mol / 1 aqueous ferric chloride solution, 1000 ml of a 1.0 mol / 1 aqueous barium chloride solution, 896 ml of a 1.0 mol / 1 aqueous nickel chloride solution and 896 ml of a 1.0 mol / 1 aqueous titanium tetrachloride solution was mixed together and the resulting solution was added to 4746 ml of a 15 mol / 1 aqueous sodium hydroxide solution at 15 to 20 ° C to form an aqueous dispersion with a pH of 14 containing coprecipitates of hydroxides of Fev Ba, ZN and Ti.

The dispersion was then subjected to the same hydrothermal reaction as in Example 1, precipitating the barium ferrite precursor of the formula BaO. 5.60 (Fe λ TiQ 16NiQ can be obtained.

The precursor was washed with water until the wash water had a pH of no more than 8 and then dried.

The particles of the precursor were mixed with an equal amount of barium chloride, calcined and washed with water to remove barium chloride, filtered and dried in the same manner as in Example 1 to obtain a microcrystalline barium ferrite powder.

The magnetic properties of the barium ferrite thus obtained and the magnetic recording properties of the magnetic tape produced using this barium ferrite are shown in the table.

Example 3.

33.97 ml of a 3.0 mol / 1 aqueous solution of ferric chloride, 1000 ml of a 1.0 mol / 1 aqueous barium chloride-35 solution, 896 ml of a 1.0 mol / 1 aqueous solution of zinc chloride and 896 ml of a 1.0 mol / 1 aqueous titanium tetrachloride solution were mixed together and the resulting solution worked up in the same manner as in Example 1 to obtain an aqueous dispersion at a pH

8502 3 1 4 -11- of 14 containing coprecipitates of hydroxides of Fe, Ba,

Zn and Ti.

The dispersion was subjected to the same hydrothermal reaction as in Example 1 to obtain precipitates of the precursor of barium ferrite of the formula

Ba0 * 5.60 iFel, 82Tl0 / l6Zn0, l603.2) *

The precursor was washed with water until the wash water had a pH of no more than 8 and dried. The particles of the precursor were mixed with the same amount of barium chloride, calcined, and washed with water to remove barium chloride, filtered and dried in the same manner as in Example 1 to obtain a microcrystalline barium ferrite powder.

The magnetic properties of the barium ferrite thus obtained and the magnetic recording properties of the magnetic tape produced therewith are shown in the table.

Example 4.

4000 ml of a 3.0 mol / 1 aqueous ferric chloride solution and 1000 ml of a 1.0 mol / 1 aqueous barium chloride solution were mixed together. The resulting solution was then added to 6300 ml of a 15 mol / 1 aqueous sodium hydroxide solution at 30 ° C to obtain an aqueous dispersion with a pH of 14 containing coprecipitates of 25 hydroxides of Fe and Ba.

The dispersion was then subjected to the same hydrothermal reaction as in Example 1 to obtain precipitates of the precursor of barium ferrite of the formula BaO 6.0, 2, 2, 3. The precursor was worked up in the same manner as in Example 1 to form a microcrystalline barium ferrite powder.

The magnetic properties of the barium ferrite thus obtained and the magnetic recording properties of the magnetic tape manufactured using this barium ferrite are shown in the table.

Comparative example 1.

The precipitate of the pre-product obtained in Example 1 was washed with water, dried and the pre-product without addition of barium chloride was calcined for 3 hours in an electric oven at temperatures of 800 ° C to form a barium ferrite powder.

Fig. 6 shows an electron microscope photograph (60000 times magnification) of the barium ferrite thus obtained. The precursor particles were found to sinter together during the calcination to form a barium ferrite powder containing large and poorly defined hexagonal particles.

The magnetic properties of the barium ferrite thus obtained and the magnetic recording property of the magnetic tape manufactured using this barium ferrite are also shown in the table, which indicates that the magnetic recording tape has a smaller square ratio than the magnetic recording tape produced. using the barium ferrite according to the invention.

15 Comparative example 2.

Barium ferrite was prepared in the same manner as in Comparative Example 1 except that the calcination temperature was 900 ° C. The resulting barium ferrite was also found to contain large and poorly defined hexagonal particles. The magnetic properties of the barium ferrite and the magnetic recording properties of the magnetic tape made using this barium ferrite are shown in the table which shows that the magnetic recording tape has a much smaller square ratio than the magnetic recording tape made using the barium ferrite according to the invention.

8302314 -13-

CM

* 0 m LD O I 00 v «. in> «. o o o oo ^ o ino o ^

O- O O IflTPCN *. -H

<n <n o o -H

rH

in

rH

**

O

1 00 HO LO 00

^ - O - O

o o oo oo in co * · o ή \ o o o m in m o ® oj co σ '1-1 in F- (*

O

o σι l ^ ». ·. m oo o o oo oiro co o * · oo in cn cn x ooi m> -) oo σι o »m + *

. iH iM

M O Ό 2 I o 0

Tj m m oo u m »» o ·> Dj n o o oo n ιη <n * ° “J ^ U ^ mo inrHCNO 08 0 oo ^ g c *

o <U

[co X! o in r-

«. - o - C

o o oo * i o o x o og Φ co oo m i> oo o ^

"^ 00 * G

, N <1)

TL O «H

η o I i> ®

• y s. LD r-0

pj O O f0 ovo o ** * ^ oo m m> -i ** ° 2m co co o S. 8.

04 O

«. m o ro oo o r- * ή v V I - ΙΛ

o o n o in cn moo g

, _i ino in oo o cnro o * oo x ·>

Sd o i ^ <U 1 m 5 ~ «Ö 0 I δ T.

• H G Ή 2 ,, fj o ΛΛΜ-λΙΙο »® -rt o ^ + J φ ^ +>> Ό +> o go Φ> X! M Sf? r · 30 -d W \ 0 0) * Ö 00 ö MG GSM ft OG ΜΗ ^ Φ M Φ -Η Φ, * ooa U £ e B Φ Φ— M tj \ m Φ 0) 4J4J ^ d MWW · Η fö 0) w ti -PHo rj S (IJ il φ φ -H »Q +> Φ Ή Φ O) β -y ®, ¾

Tl Ij X 'ft> Ö X ’-W -P m * ro a lö · Η +> TJ

03φ S Φ Φ OM-Htn + J Λ> ipw W.

Φ 5-1 Λ Φ (öOGöiMMü ^ H 5 o • g -ro xlfttnG ΦΦ ΦΜ Φ X! Φ Φ Φ Λ φφφ-Η O (d-HOOCUgO) ü -H0O O ö & i + jp u® stu o- »i ^ fl 2> · ς! dd G ^ o φ O <D TJ ® rI UI Μ Cn GO '

8 Η ί Η Λ X

8502 3 14

<A

Ö <u -14-

+ J

λ; cm rj «. Γ »

rö O UJ

0 lil vo o m i * cm

I Γ0 iH O iH

Oh, <ι <o m u o o o>

CM

m Ό

HO CM

<D r- 'tn i vo 0 *> * »m» · o iXj uncle m o σι o o' t cqm o in in η »o tj> o σι σι o h

S O

H ï> v in

CM

• H ** h tl o m <D Η mo l io

Oi O »* m * · o ρ 0 uncle cm in ή o o oo d), q o in m m«> o

J> Sn co O O rH

o H

o> m na - H ^ d) co o I m dj * - m oo uncle mor ^ o * · o ^ oo m o cm * om O cm oo oo o σι o M1 ^> in

H

Ό

pj O

0 m m i> -i 0 v *. m co

Xj uncle σ> o o o * m

Mm oo o cm oo O cm oo oo o <Tl O ih m> in

iH

> 0 * CM

h (H in o co 0 *> * I - 0 uncle cm o σι m oo, q cm oo inincMO co ρ cm oo oo - σ>

o iH O> H

0>

rH

m Ό *. o H omo σι 0 uncle - - l *> 0 oo oooom oo, q co cm o ιη σι cm or ~ - PI h oo “_ σι 0 O -P o in OH 0 I r-» Ö> Λ Λ M tn Η 0 -v Ρ 0 \ -Ρ I Ό -Ρ g O c! <D> 2 £ M <D Ö S Λ 3 O 0 Ό M g O ^ O -P cö 00 • μ -> 0 oi o 0 -p ft -p> ΰ 4 iör%. p O S - Ρ Ό ft O £ Ρ Ρ Ό Η 0 p G ft H MJl 0 ^ O G 0 0 44 0

0 43 3 0 p 4h -P Οι Ρ 0 43> m -P

43 G ft O) 0) 0 til 44 \ Oi ft-P Μ 0M

0 Ö ft ft ~ ft 44 Π Öi Ή p 0CM W O, 0 + J Η P

ft 0 44 0 44 0 O H G -P 0) Ή g 0 0 0 G -P O

ρ -H p - ini +) τΐ · ηο 44 s4 0 · Η O

01 00 0 OH 0 O 'O w Ή ft o Oi 44 O -

H ÖM0ftT3 W-PÖ-HP O 44 H. W 0 Ρ P

0 HrQ'Og-m f! 0 OilJ Φϋ Φιβ (Dg Gg00ü

> U0H0H 0 G 0 0 O W ftH 0 ft (1) -HOK

M Η 0> Ρ -Ρ -P OÖi S N Ü-H 0)> Ό - "Oi> O H

0 0 -H 0 H 0> O Wg W? D - Conclusions - 8502 3 14

Claims (7)

1. Process for preparing a microcrystalline hexagonal barium ferrite powder of a general formula: BaO. n / (Fe. M), (K / 1-mm 2 3. element in which M is at least one substituent! selected from the group 5 consisting of Co, Ti, Ni, Mn, Cu, Zn, In, Ge and Nb, m 0-0.2 and n 4.5-6.0 is characterized in that this process comprises: forming an aqueous alkaline dispersion containing coprecipitates of hydroxides of barium ions, iron (III) ions, and optionally ions of the substituent element M, in a 10 molar ratio in accordance with the general formula of the barium ferrite and with a pH of not less than about 12; heating the dispersion to temperatures of about 150-300 ° C to convert the coprecipitate a pre-product of the barium ferrite, calcining the pre-product together with a water-soluble barium halide at temperatures of about 700-1000 ° C, and washing the calcined product with water to remove the barium halide from the resulting barium ferrite. 2. Process according to claim 1, characterized in that the pre-product is mixed with the water-soluble barium halide in amounts from about 30 parts by weight to about 200 parts by weight, relative to 100 parts by weight of the pre-product. 3. Process according to claim 1, characterized in that the pre-product is mixed with the water-soluble barium halide in amounts from about 50 parts by weight to about 150 parts by weight, relative to 100 parts by weight of the pre-product. Process according to claim 1, characterized in that the water-soluble barium halide is barium chloride, barium iodide or barium fluoride. A method according to claim 1, characterized in that the barium ferrite contains Co and Ti as a substituent element. 'Λ Λ * 7 i i, Ί L 0 t -V, «r r w -16- A method according to claim 1, characterized in that the barium ferrite contains Ni and Ti as a substituent element. Process according to claim 1, characterized in that the barium ferrite contains Zn and Ti as a substituent element. 8302 3 1 4