US3038860A - Lithium nickel ferrites - Google Patents

Description

June 12, 1962 F. E. VINAL ETAL 3,038,360

' LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet l A A AVAYAYAYMYAYAYAYAYAVAYAVA #YLYAYAVAVYAYAYYAYAYAYAVA 'o.5 2 5 4)1 AAA AAAAAAAA AVAVYAVAYA AVAYAYAVAYAVAYAYAYAYAYA AVAVAYAVAVAKYMVAVAYAYAYAVAVAVAVAVA vvvvvvvnvvvvvvvvvv N'Q NiFe204 2 3) CURIEY TEMPERATURES IN c 2 4) AND SQUARENESS RATIO CONTOURS INVENTORS.

FRANCIS E. VINAL y DANIEL L. BROWN AGENT June 12, 1962 -F. E. VINALI ETAL 3 I LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 2 5 5 3 I (Zn Fe O AYAAAA AYAYAVAYAYA AYAYAYAYAVAYA I AVAYAYAYAYAYAYA YYYYYYV /V\/\/\/\/\/\/\/\/\/\ SQUARENESS RATIO CONTOURS AND CURIE TEMPERATURES IN C INVENTORJI.

FRANCIS E. VINAL BY DANIEL Lv BROWN AGENT June 12, 1962 F. E. VINAL ETAL 3,038,860

LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 3 SQUARENESS R ATIO, R S

O V 25 5O 75 100 MOLE PERCENT NICKEL FERRITE IN LITHIUM'NICKEL FERRITE INVENTORS.

, FRANCIS E. VINAL BY DANIEL L. BROWN AGENT June 12, 1962 F. EQVINAL ETAL 3,038,360

LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 4 OUTPUT (m.v.)

CALCINATION TEMPERATURE (C) INVENTORS.

FRANCIS E VINAL DANIEL L. BROWN AGENT Unite tats 3,038,360 LITHIUM NECKEL FERRITES Francis E. Vinal, Weston, and Daniel L. Brown, Boston, Mass, assignors, by mesne assignments, to the United States of America Filed Dec. 20, 1956, Ser. No. 629,666 6 Claims. (Cl. 252-625) This invention relates to a process for manufacturing ferromagnetic ceramic products and to the products so produced. More particularly, this invention relates to improved materials of the class known as ferrites,.composed of spinel compounds formed from the oxide group including lithium oxide, nickel oxide, iron oxide, zinc oxide and cadmium oxide. Ferromagnetic ceramic bodies have wide technical applications, two examples for bodies having hysteresis loops of substantially rectangular shape being switching arrays and multi-coordinate memory devices for use in the computing field. Ferrite cores with usable properties are now available, the cores normally being formed from compositions containing compounds of manganese, magnesium and iron.

Magnesium-manganese ferrite cores posses a Curie temperature in the vicinity of 250 C., such that elevated ambient operating temperatures must be avoided, yet the.

cores normally have high coercive forces resulting in the requirement of comparatively high driving currents to alter their magnetic state. Such conflicting requirements have been met in part by air cooling and close temperature control. The materials of the present invention have been found to possess improved magnetic properties, Le. a higher Curie temperature in the order of 600 C. and with substantially rectangular hysteresis loops. Thus, products made from the materials of this invention can be used at higher ambient temperatures or, more important, with higher energy dissipation than hereto-fore. The coercive force is approximately the same as that of materials in present use, being somewhat higher or somewhat lower depending upon which of the compositions disclosed is employed.

In some applications ferromagnetic ceramic bodies which have high saturation flux densities, but not necessarily rectangular hysteresis loops, are desirable. Magn esium-managanese ferrites have been modified by additional elements to increase saturation flux densities. These modifications normally produce a lowering of the Curie temperatures to values too low for satisfactory use in many applications. Materials of the present invention provide high saturation flux densities with Curie temperatures higher than unmodified magnesium-manganese ferrites.

In general, it is known that the ferrites, which are cubic crystalline materials containing Fe O and at least one other oxide, may be considered to be polycrystalline preparations of mixed crystals of the constituent compounds. The present invention, therefore, contemplates combining the constituents in proportions calculated to make chemically stoichiometric mixtures and controlling the conditions of the process to minimize loss of any metal oxide during the sintering operation. Although there have been references to lithium-nickel ferrites in the literature, notably 3,938,86 Patented June 12, 1962 Wijn et al. in Philips Technical Review, August 1954, pages 49 to 58, the processes by which useful products are obtained are not taught therein.

An obiect of this invention is to provide lithium-nickel ferrite compositions and processing methods suitable for the production of ferromagnetic ceramic products with hysteresis loops of substantially square or rectangular s ape.

Another object of this invention is to provide lithiumnickel ferrite compositions and processing methods suitable for the production of cores with short switching times.

Another object of this invention is to provide lithiumnickel ferrite compositions and processing methods suitable for the production of square loop products with high Curie temperatures.

A further object of this invention is to provide high saturation flux density lithium-nickel ferrites with high Curie temperatures.

These and other objects are obtained by utilizing a composition composed of compounds from the group including iron oxide, lithium oxide, nickel oxide, zinc oxide, and cadmium oxide and processing the composition as specified in this invention.

FIGURE 1 is a chart of composition ranges.

FIGURE 2 is a chart of composition ranges.

FIGURE 3 is a chart of composition ranges.

FIGURE 4 is a graph of squareness ratio plotted against percent nickel ferrite.

FIGURE 5 is a plot of a hysteresis loop.

FIGURE 6 is a graph of output voltages for a core being tested for use in coincident current. memory application.

FIGURE 7 is a graph of calcination temperature plotted agalnst squareness ratio.

The process of this invention is in its general aspects very similar to that currently employed for the production of ferromagnetic ceramics from compositions composed of the oxides of iron, magnesium and manganese. The first step is the intimate mixing of the proper proportions of the oxides involved, each in a fine state of subdivision. Instead of startingwith the oxides themselves it is possible to start with a mixture materials in other than the oxide form, provided the starting materials will be changed to the specified oxide duringprocessing. For example, it has been found that the use of the carbonates is convenient. The next step, if carbonates have been used, is calcining at approximately 600 C. to 850 C. for two to twenty hours. Calcining for a longer period, while unnecessary, does not appear to be harmful. The calcining step drives off the CO from the carbonates and may result in some reaction. The fact that Li CO melts at approximately 635 C. is of no concern because this compound is present in such a relatively small amount and its de composition is effected during the reaction that takes place during calcining. Experimental results have shown that the magnetic properties of the final product can be improved by controlling the calcination temperature.

In general, for each compositional mixture there can be found a combination of calcining temperature and time which results in the greatest squareness.

Most of the data in this specification is taken from range surveys. Therefore, characteristics of specific compositions are subject to some improvement by adjusting processing parameters for the specific composition.

FIGURE 7 contains plots of the squareness ratio versus calcination temperature for mixtures lying at the NiO point on line 1 of FIGURE 1. It will be seen that optimum squareness results over a to range of calcination temperature. In general, as the percent NiO.Fe O increases, the optimum calcining temperature increases. The temperature is, however, kept below that required for sintering and full reaction. Calcining as described results in material soft enough that no grinding is required at this point, although a grinding operation may be employed if desired. The third step is the addition of a binder. The particular binder used is not criti- URE 1. This figure represents all possible combinations within the ternary system:

Fe O I I TABLE I Magnetlc Properties of Lrthmm-Nzckel Ferrztes Mol percent as mixed R, Bm H H0 B,1 H Slnterlng temp. 0. L110 NlO F9203 16. 7 0 83.3 .50 1,080 2. 5 1. 5 2,960 2. 3 1, 200 15.8 2.5 81.6 .70 1, 480 2.0 1.2 2,600 1.6 1,200 15.0 5. 0 80.0 .81 1, 600 2. 3 1. 5 3, 000 2. 0 1,250 13. 3 10.0 76. 7 .81 1, 700 2. 2 1. 2 3, 200 1. 5 1,275 11.7 15. 0 73. 3 .72 1, 340 1.8 1.1 2, 750 1. 5 1,275 10. 0 20. 0 70. 0 72 1, 040 2. 0 1. 3 2, 610 1. 7 1,275 a. 3 25. 0 66. 7 .41 770 2. 3 1. 4 2, 780 2. 0 1, 275 6. 7 30. 0 63. 3 .48 490 2. l 1.3 2, 300 2.0 l, 275 3. 3 40. 0 56. 7 .57 600 1. 9 1.3 2, 300 1.8 1, 275 0 50.0 50. 0 .40 1, 060 6. 9 2. 4 2, 100 5. 3 1, 250

H... is in oersteds.

cal. The trade preparation Flexalyn, for example, has proved quite satisfactory. The fourth step is pressing the resulting mixture into the desired form. The pressure of forming should be suflicient to form a closely coherent body. The pressures used should be simply those necessary to obtain this result. 30,000 pounds per square inch has proved to be quite satisfactory. The forms may be produced by extrusion processes if desired. Usually extrusion processes are less costly but make it more difficult to hold close tolerances. The fifth step is the sintering of the resulting forms. Satisfactory results have been obtained with sintering temperatures from 1150 C. to 1325 C. and sintering times from one to ten hours. Excessive coercivity results if sintering temperatures below that recommended are employed. In general, the highest sintering temperature permissible for satisfactory products increases with a decrease in the percentage of lithium in the composition. A slab containing compounds of lithium is used to support the forms being fired. It is desirable that the percentage of lithium in the slabs be at least equal to that in the forms. The use of slabs of the same composition as the ferrites being fired is a convenient expedient. The use of these slabs containing lithium appears to minimize the loss of lithium from the forms during the firing operation. It is in this step that this invention differs importantly from processes currently in use.

The forms are not quenched after firing, but rather held in the furnace at 1000 C. to 1125 C. for six to ten hours. This anneal appears to improve magnetic properties, and inadequate annealing may be corrected by a refiring at annealing temperatures. This refiring need not be in a neutral atmosphere but may be in the normal atmosphere of the furnace. In fact, refiring in a moving neutral atmospherethe customary technique for refiring in a protective atmosphere-has proved harmful, probably because of increased loss of lithium.

The compositions involved in this embodiment of the invention may best be understood by reference to FIG- Referring to FIGURE 5, the squareness ratio R is defined as The denominator and enumer ator of the latter represent respectively the magnetization for a field |I-I and that for a field /2H It will be clear that R is also a function of the maximum field H determining the size of the loop. When R is measured as a function of H,,,, a value of 11 will be found for which R is at a maximum. In practice, an effort is normally made to use cores under conditions such that R is at or near the maximum value. If the hysteresis loop were perfectly rectangular, the squareness ratio would, of course, be 1. Practically achieved squareness ratios are always less than 1 with .80 being the figure most often used as the minimum acceptable for applications requiring substantially square or rectangular hysteresis loops. It will be noted that'FIGURE 4 shows that squareness ratios as high as .83 have been obtained. The maximum squareness ratio shown in the aforementioned Wijn paper is .78. If .80 is taken as the minimum acceptable squareness ratio, satisfactory results with the particular processing conditions used to obtain the data for FIGURE 4 were obtained over that portion of the line included between 7 to 30 percent NiO.Fe O If the cores are to be used in applications with less stringent squareness requirements so that squareness ratios of 0.6 and above may be tolerated, satisfactory results were obtained over that portion of the line included between 3 to 45 percent NiO.Fe O

The hysteresis loop obtained with a sample from the 9% nickel ferrite point on line 1 of FIGURE 1 is shown in FIGURE 5. The squareness ratio of this particular sample is .81. The dynamic result obtained in a test of the suitability of this sample for use in a magnetic core memory is illustrated in FIGURE 6. Line 10 in FIGURE 6 is the maximum allowable output from a half selected core; line 11 is the minimum allowable output from a fully selected core. For this particular memory, these limits are 30 and 80 millivolts respectively. The driving current for the test was 900 milliampe'res with a 2 to 1 selection ratio. The smallest divisions along the horizontal or time axis are .2 of a microsecond. It will be seen that this core switches in approximately 1 microsecond. It will be noted that the output as a selected core is substantially greater than the accepted minimum for this particular memory and that the output as an unselected core is substantially less than the accepted maximum.

Table II contains a tabulation of squareness ratios for varying compositional mixtures including mixtures which are not s'toichiometric and, therefore, do not lie on line 1 of FIGURE 1. These compositions and some of the Curie temperatures are plotted in FIGURE 2.

TABLE II Magnetic Properties of Lithium-Nickel Ferrites (N on-Stoichiometric) included as one of the components in the lithium nickel ferrite, the coercive force is substantially reduced. Lithiurn Zinc fenrites are not rectangular hysteresis loop materials. However, by includingzinc in the lithium nickel ferrite materials that possess rectangular hysteresis loops, relatively low coercivities and substantially higher flux densities can be obtained. Coercivity is reduced with increasing proportions of Zinc ferrite in the composition,

M01 percent as mixed R Bm H... H.; B H Sintering temp. 0.

L110 N10 F6203 17. 7 O 82.3 .63 1, 140 2. 4 1. 5 2,660 2. 1 1, 175 17. 2 1. 3 81. 5 63 1, 300 2. 5 1. 6 2, 900 2. 1 1, 175 1G. 8 2. 5 80. 7 78 1, 320 2. 4 1. 5 2, 800 2.0 1,175 16. 8 3. 8 79.8 78 1, 300 2. 4 1. 6 2, 720 2.] 1,175 15. 9 5. 1 79. 81 1, 400 2. 4 1. 2, 710 2. 0 1, 175 15.5 6. 4 78.1 77 1, 210 2. 4 1. 5 2, 790 2.0 1,175 15.0 7. 7 77. 3 .76 1, 230 2. 6 1. 7 2, 750 2. 0 1, 175 14. 1 10. 2 75. 7 75 1, 030 4. 2 2. 6 2, 680 3. 6 1,175 13. 3 12. 7 74. 0 69 830 3. 8 2. 4 2, 580 4. 2 1, 175 12. 4 15. 3 72. 3 .48 750 2. 7 1.6 2, 660 2.6 1, 175 10. 6 20. 4 69. 0 .27 840 4. 0 2. 3 2, 490 3. 4 1, 175 16. 3 3.8 79. 8 .63 1,000 2.0 1. 2 2, 980 1. 9 1, 250 15.9 5. 1 79. 0 78 1,070 2.0 1. 3 2, 310 1. 7 1, 250 15.5 6. 4 78. 1 74 1, 450 2.0 1. 3 3,080 1. 8 1, 250 15.0 7. 7 77.3 70 1, 340 2. 2 1. 4 2, 800 1. 9 1,250 14. 1 10.2 75. 7 68 1, 290 2. 7 1. 7 2, 800 2. 2 1, 250 16. 3 3.8 79.8 .62 1, 300 2. O 1. 2 2, 780 1. 8 1, 300 15. 9 5.1 79. 0 .68 1, 260 1. 8 1. 2 2, 690 1. 6 1, 300 15.5 6. 4 78. 1 .69 1, 360 1.8 1. 2 2,750 1. 7 1, 300 15.0 7. 7 77.3 63 1, 230 1. 9 1. 2 2, 830 1. 7 1, 300

and H... is in oersteds.

The ternary system of FIGURE 2 is F203L1FO2IN1F204 This system, which is actually a portion of that shown in FIGURE 1, has been chosen to expand the scale at which these results are plotted. It will be noted that lower squareness ratios and increased coercivity results from compositional variations in directions normal to the stoichiometric line. It is thought that excess Fe O gives precipitated iron oxide and/ or solid solution magnetite in the resulting material. It is thought that excess Li O gives a rock salt structure (LiFeO instead of a spinal structure Li Fe O The degradation of characteristics occurs more rapidly for excesses of Fe O than for excesses of Li O. The aforementioned use of slabs containing lithium to minimize the loss of lithium during the firing operations is important in that it minimizes unwanted compositional variations from the stoichiometric line with the resulting degradation of magnetic properties.

The values tabulated in Table II are from a range survey, and the magnetic properties of any specific composition may be improved by adjusting processing parameters. The previously noted variation of squareness ratio with calcination temperatures shown in FIGURE 7 is an example of the improvement possible by adjustment of but to maintain squareness, the percentage of nickel ferrite must also be increased. Increasing the percentage of nickel ferrite tends to increase coercivity. The best compromises with respect to high squareness and low coercivity are normally obtained from compositions with approximately one to one mol percent ratios of zinc and nickel ferrites. The addition of Zinc ferrite to the lithium nickel ferrite lowers the Curie temperature. However, the Curie temperature of the lithium nickel ferrite is relatively high so that even after an appreciable amount of Zinc ferrite has been added, about 35 mol percent, the Curie temperature of the resulting composition is still around 400 C., considerably higher than that for magnesium manganese ferrites in current use. Theprocessing considerations are the same whether or not Zinc ferrite is a component, with the exception that longer annealing times, up to twenty-four hours, are desirable.

Compositions within the ternary system are shown in FIGURE 3. Table III contains a tabulation of properties for several of these compositions.

TABLE III Magnetzc Properties of Lzzhzum-Nlckel-Zmc F errztes Ferrites, mole percent as mixed Sintering s in Hm H B 5 H55 Temp. "C

Li Ni Zn 90 5 5 .45 1, 580 1. 63 0. 99 3,690 1. 63 1,250 85 16 5 .60 1, 490 1. 66 1. 02 3, 420 1. 66 1,250 80 16 .69 1, 996 1. 66 1. 65 3, 650 1. 66 1, 256 75 16 .40 1, 366 1. 74 1. 02 3, 396 1. 86 1, 256 75 5 .73 1, 660 2. 65 1. 23 3, 136 2. 69 1,250 70 15 15 .59 930 1. 47 6. 93 3, 696 1. 47 1,250 65 36 5 .65 1, 450 2. 31 1. 49 3, 266 2. 39 1, 200 65 20 15 67 1,176 1. 31 6. s4 3, 420 1. 35 1, 256 66 23 17 72 1, 340 1. 21 0. 7s 3, 576 1. 23 1,206 60 20 20 63 1, 340 1. 15 0. 73 3, 470 1. 15 1,260 60 15 39 0 1. 18 6. 70 3,230 1. 14 1, 260 55 40 5 .44 1, 360 2. 21 1. 33 3, 166 2, 21 1,260 55 3 15 .76 1, 0 1. 34 6. 86 3, 600 1. 32 1, 206 55 25. 7 19. 3 75 1, 540 1. 22 6. 73 3, 956 1. 20 1, 250 55 20 25 50 1, 396 1. 22 0. 73 3, 390 1. 17 1, 250 56 28. 5 21. 5 71 1,610 1. 0.82 3, 650 1. 26 1,225 50 25 25 67 1, 890 1. 20 0. 77 3, 560 1. 10 1,225 56 20 30 43 1, 250 1. 19 0. 72 3, 330 1. 10 1,250 43 32 20 46 1, 440 1. 62 0. 60 3, 650 0.89 1, 175 45 20 35 1, 160 1. 69 0. 63 3, 610 0. 99 1,250 45 31. 5 23. 5 65 1, 440 1. 20 0. 74 3, 916 1. 20 1, 225 45 35 2 64 1, 416 1. 4o 6. 88 3, 390 1. 1,225 30 25 69 1, 896 1. 20 0. 77 3, 560 1.16 1,225 42 2s 30 64 1, 676 1. 14 0. 73 3,850 1. 14 1, 175 40 45 15 65 1, 550 1. 10 0. 65 3, 630 6. 97 1,225 40 46 20 .44 1, 170 1. 40 0. 90 3, 396 1. 30 1, 225 40 30 36 68 1, 520 1. 16 0. 76 3,790 1. 10 1,225 40 25 35 60 1, 640 1. 19 0. 73 3, 390 1. 09 1,225 46 20 46 .31 916 0. 91 0. 53 3, 470 6. 84 1,200 35 37. 5 27. 5 .46 1, 160 1. 15 0. 69 4, 020 1. 09 1,225 35 35 30 88 ,350 1. 02 0. 59 3, 896 0. 90 1,225 35 30 25 53 1, 230 1. 69 o. 66 3, 460 6. 98 1,225 35 25 40 .35 1, 050 0. 90 o. 53 3, 346 0. 83 1, 200 36 46 30 .48 1, 410 1. 28 0. 76 3, 440 1. 09 1,225 30 37 33 .41 1, 050 1. 07 0. 62 3, 700 0. 65 1, 256 30 35 35 .64 1, 550 1. 09 0. 65 3, 630 6. 97 1,225 30 36 40 .38 1, 010 0. 91 6. 53 3, 080 0. 86 1,260 20 30 36 1, 690 0. 94 6. 56 4,250 0. 94 1,250 20 42 3s 32 970 0. 95 0. 66 3, 580 0. 68 1, 260 100 0 o .59 1,260 2.9 1. 9 2, 766 2.8 1,260 90 0 1O 44 l, 080 1. 5 9 3, 130 1. 4 1, 200 80 0 20 .24 180 1. 5 .9 3, 810 1. 4 1,260 70 6 30 13 1, 570 1. 4 .8 4, 216 1. 2 1,200 0 40 16 1, 446 1. 1 6 4, 646 .9 1, 206 50 0 50 09 1,140 .9 .4 3, 920 .7 1, 206

H5, is in oersteds.

The values tabulated above are from a range survey, and the magnetic properties of any specific composition may be improved by adjusting processing parameters.

If 0.80 is taken as the minimum acceptable squareness ratio, satisfactory results can be obtained with compositions lying approximately within area A in FIGURE 3. If the cores are to be used in applications with less stringent requirements so that squareness ratios of 0. 6 and above may be tolerated, satisfactory results can be obtained with compositions lying approximately within area C on FIGURE 3. The change in squareness ratio with compositional variations is not as rapid in the system of FIGURE 3 as in the system of FIGURE 2. Therefore, area B has been outlined on FIGURE 3 to show the approximate area in which squareness ratios of 0.7 and above can be obtained. It may be noted that the region of highest squareness in the lithium nickel zinc ferrite when extrapolated to the stoichiometric line between lithium ferrite and nickel ferrite shown on FIGURE 1 coincides very well with the optimum region indicated on FIGURE 2 for lithium nickel ferrites which do not include zinc fenrite.

' For applications which do not require rectangular hysteresis loops, the compositions lying within area D on FIGURE 3 provide high saturation flux densities with relatively high Curie temperatures. The area of high permeability extends, theoretically, to some point near 100% ZnFe O However, increases in the zinc ferrite content progressively lower the ferromagnetic Cun'e temperature. Therefore, unless the ambient temperature is lowered as the Curie temperature is decreased, the permeability goes through a maximum as the amount of ZnFe O is increased. By virtue of the high Curie temperature of the lithium-nickel ferrites, around mol percent ZnFe O can be tolerated if the products are to be used at normal ambient room temperatures. If elevated temperatures must be encountered, Curie temperatures plotted on FIGURE 3 show that with lesser percentages of zinc ferrite Curie temperatures of 400 C. and above may be obtained for high saturation flux density compositions. The high saturation flux density area includes the areas of squareness, so that-high saturation flux density may be obtained with or without squareness as desired.

While exhaustive tests have not been made with cadmium ferrite as a component, research indicates that cadmium ferrite may be substituted on a one-for-one basis for zinc ferrite with substantially the same results.

There have thus been described improved ferrite materials exhibiting unexpected improvements in several of their useful magnetic properties. The proportions of the ingredients used should, in general, be within the percentage ranges given since use of other proportions results in products which either are not significantly improved or are inferior to previously known ferrites.

Ranges of time and temperature of heating for the calcining and sintering steps have also been given. The size of the body influences the sintering time necessary to bring about the desired properties. Very small bodies require shorter sintering times than large bodies. Also, for both steps, the required time of heating is usually in inverse ratio to the temperature used. There is usually an optimum value for heating temperature and other parameters for each composition.

Having thus described improved ferromagnetic products and processes for their manufacture, what is claimed 1. A process for manufacturing shaped lithium nickel ferrites having hysteresis loops of substantially rectangular shape comprising maintaining said shaped ferrites in direct contact with a slab containing lithium during the firing thereof, wherein the percentage of lithium in said slab is at least equal to the percentage of lithium in the lithium nickel ferrite.

2. A process for manufacturing shaped lithium nickel ferrites having hysteresis loops of a squareness greater than 0.6 and relatively low coercivity comprising maintaining said shaped ferrites in direct contact with a slab containing lithium during the firing thereof, wherein the percentage of lithium in said slab is at least equal to the percentage of lithium in the lithium nickel ferrite.

3. The process of claim 1 wherein the lithium nickel ferrite material consists essentially of Li Fe O ZnFe O and NiFe O in the proportions of about 30 to about 98 mol percent Li Fe O about 2 to about 70 mol percent NiFe O and up to 40 mol percent ZnFe O 4. The process of claim 1 wherein the lithium nickel ferrite material consists essentially of Li Fe O NiFe O and CdFe O in the proportions of about 65 to about 95 mol percent Li Fe O about 7 to about 35 mol percent Nile 0,, and up to about 35 mol percent CdFe O 5. The process of claim 2 wherein the lithium nickel ferrite material consists essentially of Li Fe O ZnFe O and NiFe O in the proportions of about 30 to about 98 mol percent Li Fe Q, about 2 to about 70 mol percent NiFe O and up to 40 mol percent ZnFe O 10 6. The process of claim 2 wherein the lithium nickel ferrite material consists essentially of Li Fe O NiFEzO and CdLFe O in the proportions of about to about mol percent Li Fe O about 7 to about 35 mol percent NiFe O and up to about 35 mol percent CdFe O References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,565,861 Leverenz et al Aug. 28, 1951 2,734,034 Crowley Feb. 7, 1956 2,736,708 Crowley et al. Feb. 28, 1956 2,751,353 Gorter June 19, 1956 2,754,172 Went et al. July 10, 1956 2,785,095 Pankove Mar. 12, 1957 2,882,234 Gorter et al. Apr. 14, 1959 FOREIGN PATENTS 759,244 Great Britain Oct. 17, 1956 1,110,819 France Oct. 19, 1955 1,115,324 France Dec. 26, 1955 1,116,092 France Ian. 23, 1956 1,116,093 France llan. 23, 1956 OTHER REFERENCES Ceramic Industry, vol. 58, No. 4, April 1952, pp. 130434.

Ceramic Industry, vol. 58, No. 5, May 1952, pp. 76-79.

Phillips Technical Review, vol. 16, No. 2, pp. 49-5 8.

Claims (1)

1. A PROCESS FOR MANUFACTURING SHAPED LITHIUM NICKEL FERRITES HAVING HYSTERESIS LOOPS OF SUBSTANTIALLY RECTANGULAR SHAPE COMPRISING MAINTAINING SAID SHAPED FERRITES IN DIRECT CONTACT WITH A SLAB CONTAINING LITHIUM DURING THE FIRING THEREOF, WHEREIN THE PERCENTAGE OF LITHIUM IN SAID SLAB IS AT LEAST EQUAL TO THE PERCENTAGE OF LITHIUM IN THE LITHIUM NICKEL FERRITE.

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