US2989474A - Ferrite with constricted magnetic hysteresis loop - Google Patents

Description

0. ECKERT June 20, 1961 FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP \Mn 2 0 H AYAYAYAYY AVA 4 YAVAVA \AA/km AMA A W I A/V v AVA 45W/W A AA MMA A A/ United States Patent Gfice 2,989,474 Patented June 20, 1961 2,989,474 FERRI'IE WITH CONSTRICIED MAGNETIC HYSTERESIS LOOP Oskar Eckert, L'auf (Pegnitz), Germany, assignor t Ste'atit-Magnesia Aktiengesellschaft, Lani (Pegnrtz), Germany, a corporation of Germany Filed Oct. 18, 1956, Sen-No. 616,818 Claims priority, application Germany Oct. 29, 1955 4 Claims. (Cl. 252-625) Ferromagnetic metals with constricted hysteresis loops (see, for example, Bozorth, Ferromagnetism, by Nostrand Co., Inc., 1951, pages 498 to 499), have, as is well known, at small field strength within the constriction area, constant permeability, i.e., permeability independent of the field strength equal to the initial permeability, very low hysteresis losses and, in general, small residual losses. As indicated in the above cited literature, such materials may be subjected to thermo-magnetic .treatment. By thermomagnetic treatment, in this connection, is meant the passing thru a thermic cycle during the simultaneous presence ofa magnetic longitudinal or transverse field. The concept of longitudinal or transverse field is, in this connection, to be understood as relative to the later measuring field; a longitudinal or transverse field, respectively, means that such field, during the thermomagnetic treatment, is parallel, respectively vertical, to the later measuring field. Thru this type of treatment, these ferromagnetic materials display a substantial alteration of the form of the hysteresis loop, and hence a change of the magnetic properties.

This invention is based on the discovery that it is possible to make specific ferrites showing a constricted magnetic hysteresis loop which are, consequently, capable of thermomagnetic treatment similarly as for metals.

The invention teaches the production of such ferrites of the manganese-nickel ferrite system which can be subjected to thermomagnetic treatment of the above type, and are distinguished from hitherto familiar ferrites by the fact that, under the same manufacturing conditions, they have constricted hysteresis loops.

In accordance with the invention, ferrites with this characteristic in the manganese-nickel-fenite system must have a composition of at least 50 mol-percent Fe O and a small addition of cobalt oxide. The addition of cobalt oxide is suitably determined between 0.1 and 5% by weight, calculated on the total basic batch of the manganese-nickel ferrite, expressed in metallic oxides. The invention has shown that it is particularly advantageous to choose the cobalt oxide content between 0.35 and 1.5% by weight, calculated on the basic batch. The manganesenickel-ferrites in question, which react strongly to the addition of cobalt oxide with a constricted loop, cover, in the three-component system Fe O -Mn O -NiO, the area defined in the attached diagram (FIG. 3) by the quadrangle A, B, C, D. The compositions at the corners in percent by Weight (see FIG. 3), are:

FezOz M11201 N 5 tween 1250 C. and 1380 C. To produce the constricted hysteresis loop in ferrites, in accordance with invention, it is necessary that the cooling takes place slowly, particularly in the temperature range between 700 C. and room temperature. The cooling speed is dependent upon the volume of the fired body. As a criterion, it may be stated that for a ring of about 46 mm. outside diameter, 34 mm. inside diameter, and 10 mm. height; the cooling time from 700 C. to room temperature should take not less than 12 hours. If the rings are cooled rapidly, the effect of loop constrictiondoes not occur. However, the constriction may be regained even for rings cooled too rapidly, by re-heating them to a temperature of about 700 C., and cooling them slowly, as above described.

An example of the invention follows hereafter:

In a steel ball mill are ground together 412.5 g. F8203, 37.5 g. M11 0 50 g. NiO, 3.25 g. C00. After 6 hours ,of grinding, the slip is poured through a 4900 mesh screen (4900 meshes per square cm.) into a porcelain dish, and dried. The powder thus obtained is pressed, according to ceramic pressing techniques, into rings having dimensions of 59 mm. outside diameter, 35.8 mm. inside diameter, and 12 mm. height, the amount of pressure applied being about 0.5 to 1 t./cm. The ferrite pieces, thus obtained, are sintered in a kiln at 1350" C. for two hours, whereupon the heat is shut off. The rings are cooled to room temperature in the kiln during a period of approximately 24 hours. The ferrite rings thus obtained are provided with 0.4 mm. copper enameled wire with windings as primary winding, and, as secondary winding, further 200 windings with 0.2 mm. copper enameled wire are applied. The oscillographic photograph of this ferrite, produced in accordance with the invention, is shown in FIG. 1, one can distinctly recognize the loop constriction of the hysteresis loop.

The following experiment proves that fern'tes produced in accordance with the invention are susceptible to thermomagnetic treatment:

.The ferrite toroid as prepared in the example, with 100 windings as a primary winding, is placed in a kiln. While heating to 600 C., and slow cooling for 12 hours to room temperature, a longitudinal magnetic field is maintained by means of the ring winding by 1 a. direct current, corresponding to a magnetic field strength of a about 15 a.-windings/cm. If the hysteresis loop of the fenrite after this thermomagnetic treatment is recorded in the same manner as described above, the result is analogous to that of metals when they are subjected to heat treatment in the longitudinal magnetic field; a complete change of the form of the hysteresis loop takes place, as may be seen in Fig. 2. In analogous manner, heat treatment in the transverse magnetic field may be carried out with corresponding effect; (see the above cited I book by Bozorth).

The technical progress obtained with such ferrites in accordance with the invention, may be seen in the following: with thermic longitudinal magnetization, for example, fem'tes with distinctly rectangular hysteresis loop may be produced which are of importance to the entire fields of electronics and for magnetic amplification, for telephone and high-frequency fields; with thermic cross magnetization, ferrites of high quality and a permeability independent of field strength may be produced, which are particularly suitable for the field of telecommunication.

I claim:

1. A process of making a cobalt-modified manganese nickel ferrite with a constricted hysteresis loop which ferrite responds to thermomagnetic treatment to alter the hysteresis loop characteristics comprising providing an intimately mixed powder composition consisting essentially of 71 to 90% by Weight of ferric oxide, 0.1 to 5% by weight of cobalt oxide and about 10% to about 2 9% by weight of metal oxides selected from the group consisting of Mn O NiO and mixtures of M11 and NiO, the proportion of said oxides being selected so that the Fe O is at least 50 mol percent of the entire mixture when the Mn O content is calculated as MnO, molding the resultant powder composition to shape and firing at about 1250 C. to 1380 C., and thereafter slowly cooling the fired product from a temperature of 700" C. down to room temperature over a period of at least about 12 hours.

2. The process as claimed in claim 1 in which the cobalt content is between 0.35 and 1% by weight of the composition.

3. A shaped and fired, cobalt-modified ferrite body of the manganese-nickel ferrite system having a constricted hysteresis loop, said ferrite being responsive to thermomagnetic treatment to alter the hysteresis loop characteristics, said ferrite containing 71 to 90% by weight of ferric oxide, from about 10% to about 29% by weight of manganese oxide, calculated as Mn O 0.1 to 5% by weight of cobalt oxide, the remainder consisting essentially of NiO, the proportion of said oxides being selected so that the ferric oxide is at least mol percent of the entire composition, said fired product being prepared by the process of claim 4.

4. The ferrite as claimed in claim 3 in which the cobalt content is between 0.35 and 1% by weight of the composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,723,239 Harvey Nov. 8, 1955 2,736,708 Crowley Feb. 28, 1956 2,882,236 Gorter et a1 Apr. 14, 1959 2,886,530 Greger May 12, 1959 FOREIGN PATENTS 735,375 Great Britain Aug. 17, 1955 1,117,385 France Feb. 20, 1956 1,125,577 France July 16, 1956 OTHER REFERENCES Economos: J. Amer. Ceramic 800., July 1955, page 242.

Weil: Comptes Rendus v. 234, pp. 1351, 1352, March 1952.

Bozorth et al.: Physical Review, Sept. 15, 1955, pages 1788-1798, particularly page 1792.

R.C.A. Review, September 1950, vol. 11, No. 3, pages 321-363, page 345 pertinent.

Claims (1)

1. 3. A SHAPED AND FIRED, COBALT-MODIFIED FERRITE BODY OF THE MANGANESE-NICKEL FERRITE SYSTEM HAVING A CONSTRICTED HYSTERESIS LOOP, SAID FERRITE BEING RESPONSIVE TO THERMOMAGNETIC TREATMENT TO ALTER THE HYSTERESIS LOOP CHARACTERISTICS, SAID FERRITE CONTAINING 71 TO 90% BY WEIGHT OF FERRIC OXIDE, FROM ABOUT 10% TO ABOUT 29% BY WEIGHT OF MANGANESE OXIDE, CALCULATED AS MN2O3, 0.1 TO 5% BY WEIGHT OF COBALT OXIDE, THE REMAINDER CONSISTING ESSENTIALLY OF NIO, THE PROPORTION OF SAID OXIDES BEING SELECTED SO THAT THE FERRIC OXIDE IS AT LEAST 50 MOL PERCENT OF THE ENTIRE COMPOSITION, SAID FIRED PRODUCT BEING PREPARED BY THE PROCESS OF CLAIM 4.

Images