US2950251A

US2950251A - Magnetic materials having rectangular hysteresis characteristics

Info

Publication number: US2950251A
Application number: US534954A
Authority: US
Inventors: Robert S Weisz
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-09-19
Filing date: 1955-09-19
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. 23, 1960 R. s. WEISZ 2,950,251

MAGNETIC MATERIALS HAVING RECTANGULAR HYSTEREISIS CHARACTERISTICS MOL 2/26 [/1404 "/0 5 0 @5 MOL 240 [2 54mf2; 0

Filed Sept. 19, 1955 0 6' 5 M01 2710* 5mm 705 0 3- 3 INVENTOR. Foamr 5. W952 United rates Fatent Q MAGNETIC MATERIALS HAVINGJZECTANGU- LAR HY STERESIS CHARACTERISTICS Robert Weisz, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Sept. 19, 1955, Ser. No. 534,954

12 Claims. (Cl. 252-625) This invention relates to improved ferrospinel compositions and methods of making them. More particularly it relates to improved ferrospinel compositions having hysteresis characteristics particularly adapted for use in saturable reactor devices.

The term ferrospinel as used herein refers to ferromagnetic oxide compositions, also known as ferrites, which include iron oxide and have essentially a spinel crystal structure. Ferrospinel is more definite than the term ferrite which has been used to refer to any compound formed when ferric oxide is combined with a more basic metallic oxide. Ferrite is a broader term than ferrospinel and may be used to refer also to compounds that do not have a spinel crystal structure.

Many different ferrospinel compositions have been prepared and described previously. As a class these compositions exhibit advantageous magnetic properties including high magnetic permeability and low electrical losses. Certain of the previously described materials also have a nearly rectangular hysteresis loop and a low coercive force such that they are especially adaptable for use as saturable reactors. For example, in magnetic memory devices it is desirable to provide a magnetic core that may be saturated by a magnetizing pulse of unit magnitude but substantially unaffected by a magnetizing pulse of /2 unit magnitude. This requirement and the reasons for it are explained in detail in an article by Jan A. Rajchman in the Proceedings of the I.R.E., October 1953, page 1407. Only materials having hysteresis characteristics with a high degree of rectangularity satisfactorily meet this requirement. Previously lmown materials having substantially rectangular hysteresis loops include ferrospinels of the manganese-magnesium system and manganese-lithium ferrospinels including one or more of magnesium, zinc, cadmium, nickel and copper ferrospinels in solid solution.

One object of the instant invention is to provide novel ferrospinel compositions having improved magnetic characteristics particularly adaptable for use in saturable reactors. A further object is to provide improved methods of making these compositions to optimize their magnetic characteristics.

These and other objects are accomplished according to the instant invention by ferrite compositions comprising 40-47% Fe O 4055% MnO and 515% ZnO or CdO on a molar basis. ZnO and CdO are equivalents in the composition of the invention and may be substituded one for the other in any proportion, ZnO being preferred because of cost. The optimum processing temperatures are specified hereinafter for several specific compositions with n the scope of the invention. In general, optimum results are provided when the compositions are heated at about 1075" to 1275 C. for about one hour. After the compositions are fired they are cooled relatively rapidly by withdrawing them from the furnace and exposing them to the atmosphere at ordinary room temperatures.

The invention will be described in greater detail in ice connection with the accompanying drawing of which:

Figure l is a line graph illustrating the variation in a quality factor as a function of the zinc content of several compositions of the invention;

Figure 2 is a line graph of a different quality factor from that shown in Figure 1 but with respect to the same compositions and as a function of the same variant; and,

Figures 3 and 4 are line graphs of the same quality factors described in Figures 1 and 2, respectively, but showing the variations of the quality factors in different compositions, from those shown in Figures 1 and 2.

The compositions of the instant invention may be initially prepared in a manner similar to other ferrospinel compositions. Raw metallic oxides or their equivalents are mixed together and pulverized as by wet milling in a ball mill for one hour or more. Generally, it is not necessary to use the metallic oxides themselves as raw ingredients. Equivalent quantities of any compounds that will decompose at elevated temperatures to yield the desired oxides may be substituted therefor. For example, where extreme purity is desired it is preferred to use manganese carbonate instead of any of the commercially available forms of manganese oxide.

The milled oxide mixture is dried and calcined by heating it at about 900 C. for about one hour. After calcining, the mixture is again milled to reduce its particle size and to insure intimate mixing of the oxides.

An organic binder such as parafiin or a resin and a lubricant such as stearic acid are usually added to the mixture to facilitate molding. The particular binder and lubricant used are not critical. About 4% by weight of a 50% water suspension of parafi'in may be used as a binder and about 1% by weight stearic acid may be added as a mold lubricant, the weight percents being based on the total weight of the final mixture. The mixture is molded into core bodies by any convenient method such as by pressing in a die, after which the molded bodies are heated at about 400 to 500 C. to burn off the binder and the lubricant. The bodies are then fired for about one hour at a temperature between 1075 and 1275 C. The firing temperatures are relatively critical to provide optimum electrical properties in the compositions. A change of 25 C. almost invariably seriously affects the electrical properties of the materials, and in some cases, a change of as little as 5 C. may reduce the electrical properties to below commercially acceptable limits. The time for which the bodies are held at their firing temperatures, on the other hand, has been found not to be critical. This is shown, for example, by the composition code number 5 listed in the table, which was fired for 18 hours and still exhibits excellent electrical properties.

A representative group of different compositions within the scope of the instant invention is listed in the table.

TABLE Composition-M01. Percent Firing Code No. Temp., D H D/H lD/H ZnO C Fe O; or MnO CdO critlcal.

1 Fired and cooled in nitrogen atmosphere.

. air, or other oxidizing atmosphere.

states at different temperatures.

About 1 lb. a the hired oxides may be laced in a steel ball mill with about a pint of water or alcohol and milled for about one hour. The' milled mixture is calcined by heating it in air or an ordinary kiln atmosphere at about 1000 C. for about'one hour. The calcined mixture, now at least-partly reacted and comprising a substantial proportion of a ferrospinel composition together with some unreacted oxides is again wet ground in a ball mill for at least one hour and preferably for about six hours. About 4% by Weight of a 50% water changes of two hysteresis loops, one of the loops being emulsion of paraffin and about 1% by weight Trigazmine oleate' are added to the mixture after it is ground and 7 dried. The parafiin serves as a binder and the oleate as a mold lubricant in the subsequent molding step. The resulting mixture is a relatively thin paste which is dried so that it may be directly molded or cut into pellets for greater convenience in molding. The mixture in bulk or pellet form is molded by pressing in a die to form a shaped core body such as a toroid, or annulus. The core bodies are heated at'about 400 to 500 C. to burn oifthe binder and the lubricant. in a high temperature kiln where they are heated to about 1175 C. and maintained at that temperature for about one hour. After one hour the bodies are withdrawn They are then placed from the kiln and exposed to the atmosphere at room temperature so that they may be rapidly cooled.

The cooling step is preferably accomplished as rapidly as can possibly be donewithoutdamaging the core bodies. Generally, the bodies must be left on their setter plates for cooling; otherwise they may cool so rapidly that they develop cracks due tothermal strains. If the bodies are cooled slowly their electrical properties are usually adversely' afiected, especially if they are cooled in an to be due to the unstable, ambivalent nature of manganese.

This effect appears At the firing temperaturethe manganese, it is believed, assumes lattice sites corresponding to an optimum, but unknown, state of oxidation. If the bodies 'are cooled slowly the manganese has an opportunity to reorient itself in the crystal structure in less advantageous positions, or to change its condition in some other manner due to its tendency to assume different oxidation When the bodies are quenched, on the other hand, the manganese is frozen in the position and oxidation state it assumed at the firing temperature.

For purposes of comparing the magnetic properties of V l the materials of the invention test toroids' of the materials are prepared as heretofore described. They are all a made of a uniform size, having an outside diameter of about 0.5 cm., an inside diameter of 0.3 cm. and a height of about 0.1 cm. They are wound with a primary, input winding of five turns and a secondary, output winding of one turn, each of A.W.G. No. 33 copper wire. The

hysteresis characteristics of the materials are determined generated by an alternating current of unit magnitude, and the other one being generated by an alternating current of one-half unit magnitude. In most known material this ratio varies according to the absolute value of the unit magnitude, some materials requiring a relatively large driving current to'maximize the ratio, others requiring a relatively small driving current. H is. the current, expressed as ampere-turns, that results in the maximum ratio, .01. optimum discrimination.

Due to variations in individual test techniques the values of D as determined by dilferent experimenters cannot be expected to match perfectly. They should, however, correspond inthat, for any two given materials, all methods of determining D will agree as to which one is better than the other. The values of D stated herein are, therefore, relative only, and are not intended as absolute values.. i a

The composition of a suitable figure of merit taking both discrimination and driving current into account is relatively severe, the second figure of merit may be preferred.

The variations of these two figures of merit are shown in the drawing as functions of the various compositions shown in the table. Figure 1 describes the first figure of merit, D/H, as a function of the zinc oxide proportion in ferrospinel compositions including manganese oxide and 45 mol. percent iron oxide. It will be noted that the quality figure is at a maximum when the zinc oxide comprises about 5% of the total composition. Figure 2 illustrates the variation of the second figure of merit, D/H with respect to the same compositions described in Figure 1. This curve shows a relatively sharp maximum at about 10% Zinc oxide. Figure 3 corresponds in general to Figure 1 except that the compositions of Figure 3 comprise only 40 mol. percent Fe O instead of 45 mol. percent. Again it will -be noted that in these compositions, also, the D/H figure of merit reaches a maximum at about 5% zinc oxide. Figure 4 describes the variation of the second figure of merit, D/H with respect to the same compositions as described in Figure 3. It,'too shows a maximum at about 5% zinc oxide concentration.

Except for the firing'temperature the processing of the compositions of the invention is not critical but may be accomplished according to conventional techniques. The oxides,.for example, instead of being ground initially to pulverulent form may be precipitated from an aqueous solution in such form that they require no further grind- There have thus been described improved ferrospinel' compositions and methods of making them, which compositions. are particularly adapted for use in saturable reactors.

What is claimed is:

1. Magnetic composition having a substantially rectangular. hysteresis characteristic prepared by firing between 1075 and 1275 C, for at least about onehour and then rapidly cooling a formed body consisting essentially of:

M01. percent At least one material selected from the group consisting of ZnO and CdO MnO Balance 2. Magnetic composition having a substantially rectangular hysteresis characteristic prepared by firing between 1075 and 1275 C. for at least about one hour and then rapidly cooling a formed body consisting essentially of:

Mo]. percent F203 At least one material selected from the group consisting of ZnO and CdO 4-15 tangular hysteresis characteristic prepared by firing between 1075 and 1275 C. for at least about one hour and then rapidly cooling a formed body consisting essentially of on a molar basis about 45% Fe O 50% MnO and 5% of at least one material selected from the group consisting of ZnO and CdO.

5. Magnetic composition having a substantially rectangular hysteresis characteristic prepared by firing between 1075 and 1275 C. for at least about one hour and then rapidly cooling a formed body consisting essentially of on a molar basis about 45% Fe 45% MnO and 10% of at least one material selected from the group consisting of ZnO and CdO.

6. Magnetic composition having a substantially rectangular hysteresis characteristic prepared by firing between 1075 and 1275 C. for at least about one hour and then rapidly cooling a formed body consisting essentially of on a molar basis about 45% Fe O 40% MnO and 15% of at least one material selected from the group consisting of ZnO and CdO.

7. Magnetic composition having a substantially reotangular hysteresis characteristic prepared by firing between l075 and 1275 C. for at least about one hour and then rapidly cooling a formed body consisting essentially of on a molar basis about 47% Fe O 48% MnO and 5% of at least one material selected from the group consisting of ZnO and CdO.

8. Method of making a magnetic material having a substantially rectangular hysteresis characteristic comprising mixing together pulverulent metallic oxides in the molar proportions of about 40% Fe O 55% MnO and 5% of an oxide selected from the group consisting of Z n0 and 6 CdO, molding said mixed oxides to form a shaped body and firing said shaped body at about 1075 C. for at least one hour thereby to react said oxides and to sinter said body, and rapidly cooling said body from its firing temperature.

9. Method of making a magnetic material having a substantially rectangular hysteresis characteristic comprising mixing together pulverulent metallic oxides in the molar proportions of about 45 Fe O 50% MnO and 5% of an oxide selected from the group consisting of ZnO and CdO, molding said mixed oxides to form a shaped body and firing said shaped body at about 1175 C. for at least one hour thereby to react said oxides and to sinter said body, and rapidly cooling said body from its firing temperature.

10. Method of making a magnetic material having a substantially rectangular hysteresis characteristic comprising mixing together pulverulent metallic oxides in the molar proportions of about 45% Fe O 45% MnO and 10% of an oxide selected from the group consisting of ZnO and CdO, molding said mixed oxides to form a shaped body and firing said shaped body at about 1175 C. for at least one hour thereby to react said oxides and to sinter said body, and rapidly cooling said body from its firing temperature.

11. Method of making a magnetic material having a substantially rectangular hysteresis characteristic comprising mixing together pulverulent metallic oxides in the molar proportions of about 45 Fe O 40% Mn() and 15% of an oxide selected from the group consisting of ZnO and CdO, molding said mixed oxides to form a shaped body and firing said shaped body at about 1275 C. for at least one hour thereby to react said oxides and to sinter said body, and rapidly cooling said body from its firing temperature.

12. Method of making a magnetic material having a substantially rectangular hysteresis characteristic comprising mixing together pulverulent metallic oxides in the molar proportions of about 47% Fe O 48% MnO and 5% of an oxide selected from the group consisting of ZnO and CdO, molding said mixed oxides to form a shaped body and firing said shaped body at about 1200 C. for at least one hour thereby to react said oxides and to sinter said body, and rapidly cooling said body from its firing temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,551,711 Snoek et al. May 8, 1951 2,579,978 Snoek et a1 Dec. 25, 1951 2,636,860 Snoek et al. Apr. 28, 1953 2,640,813 Berge J1me 2, 1953 FOREIGN PATENTS 683,722 Great Britain Dec. 3, 1952 697,219 Great Britain Sept. 16, 1953 518,380 Belgium Mar. 1, 1953 1,093,965 r e -.-,---Y---. e 5

Claims

2. MAGNETIC COMPOSITIONS HAVING A SUBSTANTIALLY RETANGULAR HYSTERESIS CHARACTERISTIC PREPARED BY FIRING BETWEEN 1075* AND 1275*C. FOR AT LEAST ABOUT ONE HOUR AND THEN RAPIDLY COOLING A FORMED BODY CONSISTING ESSENTIALLY OF: