US2982731A - Modified nickel ferrite - Google Patents

Description

United States Patent C MODIFIED NICKEL FERRITE Donald H. Baird, New York, Joseph John Dymon, Flushing, and Samuel Natansohn, Brooklyn, N.Y., assignors,

by, mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware No Drawing. Filed June 13, 1957, Ser. No. 665,591

1 Claim. (Cl. 252-625) Our invention is directed toward ferrite materials and more particularly relates to ferrite materials which find application at microwave frequencies.

It is known that when an electromagnetic wave propagated at microwave frequencies is supplied to a circuit element formed from magnetized ferrite material, the permeability of this element does not have a constant value but rather varies in accordance with variations in the wave polarization. This variable permeability is extremely useful in microwave applications.

.Ferrite materials of this type, when magnetized by a direct magnetic field, will absorb a large percentage of incident electromagnetic energy when this energy falls Within a given narrow band of frequencies, the frequency range being determined by the intensity of the magnetic field. The frequency band is defined as the ferromagnetic resonance absorption band. I V

In conventional circuit applications, ferrite materials are used at frequencies which exceed the frequencies falling within the absorption band. Since the frequencies in the absorption band are uniquely specified by a given value of field intensity, in order for a ferrite element to be operated at frequencies above those in the absorption band, the field intensity must be reduced below this given value.

The field intensity, however, cannot be reduced indefinitely. When the field intensity is reduced sufficiently to permit operation at relatively low, microwave frequencies, the permeabilities of conventional ferrites become erratic and unpredictable. More specifically, in conventional ferrites it is found that this erratic behavior can be expected when the frequencies to be used expressed in megocycles per second are less than approximately 2.8 times as large as the saturation magnetization of the ferrite expressed in gauss. Hence, it is desirable to adjust the saturation magnetization in accordance with the operating frequency desired.

In addition to the saturation magnetization, two other parameters of ferrite materials become important in microwave applications. The first of these, the Curie temperature, is a measure of the maximum temperature use to which ferrite materials can be subjected without losing their magnetic properties and hence becoming un-' usable. Since these materials necessarily absorb energy during operation and are thereby heated, the Curie temperature limits the power handling capacity of devices incorporating such materials. The second parameter, the dielectric loss, is a measure of energy absorbed by a ferrite during operation and, to reduce insertion losses and increase efiiciency in devices utilizing such material, must be as small as possible.

We have invented a new type of ferrite material which has a low dielectric loss, a relatively high Curie temperature, and a saturation magnetization which can be varied at will over a wide range.

Accordingly it is an object of our invention to provide new and improved ferrite materials characterized by a low dielectric loss, a relatively high Curie temperature, and a saturation magnetization variable over a wide range.

Another object is to improve ferrite materials operable at radio or microwave frequencies by increasing the Curie temperature and decreasing the dielectric loss of such materials at these frequencies.

Still another object is to provide new and improved ferrite materials operable over a wide frequency range and having a saturation magnetization which can be varied in accordance with any chosen frequency within said range.

These and other objects of our invention will either be explained or will become apparent hereinafter.

In accordance with the principles of our invention, the oxides of manganese, nickel, iron and aluminum are reacted together in the solid state to produce our ferrite material. The proportional concentration of each oxide in the total mixture, as expressed in molecular ratios, is defined by the approximate formula z s-l-( 2 3 wherein (a) ranges between 0.02-0.10, and the quantity (b-i-c) ranges between 0.95-0.99. The ratio c/b can in principle have any value, but our best results have been obtained when the ratio c/b falls within the approximate range 0-1.

We have found that depending upon the particular composition selected, the saturation magnetization can be varied at will within the approximate range -2700 gauss with a corresponding range of Curie temperature from 275 to 575 C. Further, the dielectric loss as expressed in terms of the dielectric loss tangent at a frequency of 10 megacycles per second (the dielectric loss tangent is a measure of the conductivity of a ferrite material when used as a dielectric in a capacitor) can be as low as 0.002 for compositions covering this entire range.

In the copending patent application of D. H. Baird and J. J. Dymon, filed January 3, 1956, Serial No. 557,- 429, there is disclosed a process for producing ferrites in which suitable compounds of the metallic elements are first mixed together in the proper proportions and fired in air at a temperature of about 950 C. The mixture is then subjected to one or more calcining operations with intermediate pulverizing steps if required. The material is then pulverized once more with addition of suitable binding or plasticizing agents and is pressure molded into a compact. The end product is then produced by firing in air at a temperature between 1350 C. and 1500" C. for a period of from 6 to 10 hours and then cooling this compact.

Our materials can be produced in accordance with the process taught in the above identified application or alternatively can be produced in accordance with more conventional ceramic processing techniques.

Our invention will now be described in detail with reference to the illustrative example which follows.

EXAMPLE Various ferrite materials satisfying the formula were prepared under such conditions that (a) was held constant at .06 and the quantity (b+c) was held constant at 0.970. The saturation magnetization, Curie temperature, and dielectric loss tangent (measured at a frequency of 10 megacycles per second) were then determined for each formation as indicated in Table I below.

As indicated by the above data, when quantities (a) and (b-l-c) are held constant and the ratio g is the values of the saturation magneization and Curie temperature of the material approach the corresponding values of nickel ferrite (which has a saturation magnetization of approximately 3000 gauss and a Curie temperature of approximately 580 C.) As the ratio c/ b is increased, the saturation magnetization decreases rapidly, and the Curie temperature decreases at a relatively slow rate. Since A1 0 and 'Fe O will always form a solid solution, irrespective of the relative proportions of each component, the ratio c/b can take any value between Zero and infinity. However, our best results have been obtained when the ratio c/b does not exceed 1.

When the quantity (b+c) is increased from .97 toward a maximum of about .99, and the ratio the values of the saturation magetization and Curie temperature of the material approach more closely the corresponding values of nickel ferrite. When this quantity (b-i-c) is decreased toward a minimum of about .95, the difierence between the values of saturation magnetization and the Curie temperature of the material and the corresponding values of nickel ferrite become more accentuated.

The manganese oxide content (a) determines, at least in part, the dielectric loss tangent of the material. When no manganese oxide is present for example, the dielectric loss tangent of the resulting ferrite can exceed 1; such material will have a very high insertion loss andvwill be extremely ineificient. In order to reduce the dielectric loss tangent to an acceptable low value, (a) should have a minimum value of about 0.02. On the other, hand,

as (a) is increased, the loss tangent tends to decrease. However, an excess of manganese oxide will adversely influence the magnetic properties of the ferrite, such as the Curie temperature, so that (a) should have a maximum value of about 0.10. Since the valencies of the manganese in this product cannot be accurately evaluated at present, it will be understood that the manganese in the product is not necessarily in the divalent state.

While we-have shown and pointed out our invention as applied above, it will be apparent to those skilled in the art that many modifications can be made Within the scope and sphere of our invention as defined in the claim which follows.

What is claimed is:

A ferrite material made by firing the oxides NiO, MnO, Fe O and A1 0 in air at a temprature of about 950 C., mixing the product with a binding agent and sintering in air at a temperature between 1350" C. and 1500 C. for a period of 6 to 10 hours, said original components of NiO, MnO, Fe O and A1 0 being defined by the approximate formula (1) NiO-l-(a) MnO-i-(b) Fe2 3+(C) A1 0 wherein the quantities (l), (a), (b), and (c) are mole ratios, the quantity (a) being equal to 0.06, the quantity ,(b-l-c) being equal to 0.97, and the ratio c/b falling within the approximate range 0084-0482, the dielectric loss tangent of said ferrite material falling within the range 0001-0008, the Curie temperature falling within the range 285 C.-530 C., and the saturation magnetization falling within the range -2000 gauss.

References Cited in the file of thispatent UNITED STATES PATENTS 2,179,810 Brill "Nov. 14, 1939 2,565,861 Leverenz et al. Aug. 28, 1951 FOREIGN PATENTS 82,278 Netherland Aug. 5, 1956 1,117,385 France Feb. 20, 1956 1,122,258 France May 22, 1956 OTHER REFERENCES