US3246263A

US3246263A - Temperature stabilized gyromagnetic element

Info

Publication number: US3246263A
Application number: US269034A
Authority: US
Inventors: John G Clark
Original assignee: Sperry Rand Corp
Current assignee: Unisys Corp
Priority date: 1963-03-29
Filing date: 1963-03-29
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12

Description

3,246,263 TEMPERATURE STABILIZED GYROMAGNETIC ELEMENT Filed March 29, 1963 J. G. CLARK April 12, 1966 2 Sheets-Sheet l 100 AXIS HARD 111 AXIS EASY 110 PLANE FIG.2.

INVENTOR /0/-//V G CLARK QAmkM ATTORNEY April 12, 1966 J, CLARK 3,246,263

TEMPERATURE STABILIZED GYROMAGNETIC ELEMENT Filed March 29, 1965 2 Sheets-Sheet 2 ROOM TEMP 0 3O RE'hATIVE ELD STRENGHT INVENTOR. J0H/v GA CLARK ATTORNEY United States Patent Delaware Filed Mar. 29, 1963, Ser. No. 269,034 4 Claims. (Cl. 333-241) This invention relates to temperature stabilization of electromagnetic wave devices using magnetically polarizable gyromagnetic materials, and more particularly relates to the substantial elimination of variations in the magnitude of the effective internal magnetic field within the polarized material due to the change or drift in magnitude, as a function of temperature change, of the anisotropy field in an elliptically shaped member of a gyromagnetic material having a single cubic crystal structure.

Magnetically polarizahle gyromagnetic materials are used quite extensively in electromagnetic wave devices and circuits because of their ability to introduce into the circuits reciprocal or non-reciprocal coupling, attenuation, phase shilit, power limiting, frequency conversion, etc. The effective internal magnetizing field H within a magnetically polarizable gyromagneti-c material ordinarily is a function of the saturation magnetization M of the material, the applied biasing magnetic field H the anisotropy field H associated with the particular material, and the demagnetization fields H which are a function of the shape of the specimen of the material used. The saturation magnetization M the anisotropy field H and the demagnetization fields H all are temperature dependent so that the internal magnetization field varies as the temperature of the material changes due to changes in ambient temperature, and/or because of the rise in temperature resulting from the absorption of electromagnetic wave energy within the material. This change in internal magnetization field is undesirable because it results in changes in the operating characteristics of the material and thus of the device or circuit employing the material.

In recent years small, highly polished, single crystal spheres of gyromagnetic materials have been used in devices such as gyromagnetic couplers to perform the functions of power limiters and filters, for example. The small spheres have been used at least partially because the effects of the saturation magnetization term M and the demagnetization fields H, are substantially eliminated because of the spherical shape, thus eliminating the problem associated with temperature dependence of these two quantities. The temperature dependent variations in the operating characteristics of small, highly polished spheres of single crystal material are not entirely eliminated in known devices, however, because the anisotropy field associated with the crystalline structure of the material still is temperature dependent, and in devices employing the single crystal spheres as coupling elements between two waveguides, for example, the problem still is of concern. The reason for this is as follows. The single crystal sphere of gyromagnetic material is magnetized to its gyromagnetic resonance condition in order to efficiently accomplish its coupling action, and since the resonance line width of a single crystal sphere of yttrium iron garnet, or similar cubic crystal material that commonly is employed, is very narrow, any slight change in the internal magnetization field of the material results in a change in the resonant frequency of the mate rial, thus significantly affecting the gyromagnetic coupling action performed by the spheroid of material.

It therefore is an object of this invention to temperature stabilize the operation of an electromagnetic wave device employing a small, highly polished sphere of a gyromagnetic material having a single cubic crystal structure.

Another object of this invention is to substantially eliminate variations in operating characteristics, due to temperature changes, in an electromagnetic wave device employing a gyromagnetic material having a single cubic crystal structure by eliminating from the internal magnetic field within the material the effects caused by the variations in the anisotropy field resulting from the temperature changes.

A further object of this invention is to eliminate the influence of temperature dependent anisotropy field changes on the internal magnetic field of a magnetically polarized single cubic crystal ellipsoid of gyromagnetic material.

In accordance with this invention, the change in the internal magnetization field of a small spheroid of a single cubic crystal gyromagnetic material that results from the change or drift in magnitude of the anisotropy field associated with the crystal is substantially eliminated by aligning the crystalline structure of the material with respect to the biasing magnetic field so that said biasing field is applied parallel to the 110 plane of the crystal and is inclined at an angle of approximately 30 to the 100 axis of the crystal.

The present invention will be described by referring to the accompanying drawings wherein FIG. 1 is a simplified illustration of an electromagnetic wave device whose performance may be improved in accordance with the teachings of the present invention;

FIG. 2 is a diagrammatic illustration showing the crystallographic orientation of a single cubic crystal of a gyromagnetic material with respect to the direction of the applied biasing magnetic field so as to eliminate the temperature variations in the strength of the internal magnetic field that are caused by the temperature dependent anisotropy drift commonly associated with these materials; and

FIG. 3 is a graphic illustration substantiating the improved results achieved in a device constructed in accordance with this invention.

Referring now in detail to the accompanying drawings, the crystallographic alignment of an ellipsoid of gyromagnetic material having a single cubic crystal structure, as taught by this invention, is particularly useful in a gyromagnetic coupling limiter device of the type illustrated in FIG. 1. This device is adapted to propagate electromagnetic waves in the TEM mode and is comprised of a short cylindrical body member 10 having coaxial line input and output connectors 11 and 12 disposed at with respect to each other on the cylindrical surface of body member 10. Conductive bottom plate 14 completely encloses the bottom portion of body mem ber 10, and a similar conductive plate, not shown, is adapted to enclose the other end of body member 10. The

inner conductors

17 and 18 of coaxial line connectors 11 and 12 extend through apertures in body mem ber 10 and connect with thin

conductive strips

20 and 21 which extend radially in overlapping relationship with respect to each other. Disposed between

conductive strips

20 and 21 and in intimate contact therewith, is a small highly polished ellipsoid or sphere 22 of a low loss single cubic crystal gyromagnetic material such as yttrium iron garnet, gallium substituted yttrium iron garnet, lithium ferrite, or a similar single cubic crystal material suitable for use in known devices of this type. As is well known, the spheroid of gyromagnetic material functions in a manner similar to a resonator to couple electromagnetic wave energy between

conductive strips

20 and 21. In the typical use of the device of FIG. 1 as a gyromagnetic coupling resonator, high power pulses of electromagnetic waves may be coupled into coaxial line input terminal 11 and are coupled from strip conductor 2% through single crystal sphere 22 to strip con ductor 21. The spheroid 22 of gyromagnetic material operates in response to this high power pulse to couple to output coaxial connector 12 only the energy up to some threshold power level, the remainder of theenergy above this threshold level being dissipated in the spin waves associated with the precessing magnetic moments of the electrons of the gyromagnetic material. To operate in this manner the single crystal sphere 22 ofgyromagnetic material is magnetically polarized or biased in a direction transverse to the plane of the paper to its g'yromagnetic resonance condition. The single crystal sphere of yttrium iron. garnet, and other similar materials of single crystal cubic structure, is characterized.

by having a very narrow gyromagnetic resonance line width, and any etfect, such as a change in the internal magnetization field of the spheroid, which tends to change the gyromagnetic resonance frequency of the sphere, has an appreciable effect on the operating characteristics of the device. One reason for using the spherical shape for the element of gyromagnetic material is to eliminate the demagnetization fields and the influence of saturation magnetization M from the gyromagnetic resonance phenomenon since both of these quantities are temperature dependent and would cause a change in the internal magnetization of the sphere, and thus a change in the resonant frequency of the sphere as its temperature increases due to absorption of the electromagnetic Wave energy experienced as a result of its power limiting action.

With the saturation magnetization M and the demagnetizing fields eliminated from the gyromagnetic resonance equation, the effective resonance field for the single crystal sphere may be expressed in this simplified form:

ert mnll o+ annl wherein H is the effective internal magnetic field requlred for gyromagnetic resonance,

H is the external magnetizing field applied parallel to the 110 plane of the crystal.

H is the anisotropy field associated'with the cubic crystal structure of the material and is equal to K 4TrM where K is the first order anisotropy constant and M 7 is the saturation magnetization of the material,

magnetic field H is substantially eliminated so that the I efiective internal resonance field H is a function only of the applied magnetic field H which is, or can be made, substantially independent of temperature.

The effect of the anisotropy drift on the effective inwith respect to the applied magnetic field H so as to minimize this effect. This desired orientation may be arrived at as follows. Expanding Equation 1 above results in the following expression:

Further, theoretical and experimental evidence indicates that the H termis small with respect to the other terms in the equation and may be dropped. Equation 2 therefore reduces to Since the second term on the right side of Equation 3 is the only one involving the anisotropy field that has temperature dependent characteristics, the desired temperature stable operation of a device employing the single crystal sphere may be obtained if this term can be eliminated. This indeed may be accomplished by setting the quantity (A-l-B) equal to zero. This term reduces to zero when the value of in the expressions. for A and B is equal to 29 degrees minutes.

FIG. 2-is a diagrammatic illustration showing the angular alignment of the magnetic biasing field H with respect to the crystallographic structure of a single crystal sphere of yttrium iron garnet or other suitable gyromagnetic material having a single cubic crystal structure. As illustrated in FIG. 2, the magnetic biasing field H is 7 applied parallel to the 110 plane of the cubic crystal and ternal resonance field H is dependent upon the orienta- 7 tion of the crystalline structure of the gyromagnetic sphere with respect to the direction of the applied magnetic field 1-1 and in accordance with this invention, the crystal structure of the single crystal sphere is oriented is inclined at an'angle of 29 degrees 40 minutes to the 100 axis of the crystal. When the specimen of the single cubic crystal gyromagnetic material is crystallographically oriented with respect to the external biasing or polarizing field in the manner illustrated in FIG. 2, the temperature variations in the anisotropy field no longer have any appreciable effector influence on the magnitude of the effective internal resonance field H and the operation of an electromagnetic wave device that utilizes the crystal is substantially stabilized against temperature changes. i

The inclination of the magnetic biasing field H at an angle of 29 degrees 40 minutes with respect to the 100 axis, which is the hard axis of magnetization, represents a departure from known practice wherein it is customary to apply the magnetizing field H parallel to the 111 axis of the crystal, which is the easy axis of magnetization. The prior practice of magnetizing the crystal parallel to its 111 axis was followed in an attempt to reduce the required strength of the applied magnetizing field. However, as pointed out above, this leaves an effective H term in the'gyromagnetic resonance equation, and this term which is subject to change in magnitude with changes in temperature of the material causes a resultant change in the value of effective internal magnetic field H I r The effectiveness of the above-described means for temperature stabilizing'the operation of an electromagnetic wave device employing a single crystal sphere of yttrium iron garnet, for example, has been verified in practice and typical results are illustrated in the graph of FIG. 3 which is a polar plot, for various temperatures, of the effective resonance field H as a function of the angle between the direction of the magnetizing field H and the 100 axis of a single cubic crystal. As may be seen from FIG. 3, the effective field for resonance H varies considerably with temperature. It will be noted, however, that the curves for the three temperatures, room temperature, 55 C., and C. intersect whenever the direction of the magnetizing field is at an angle-of approximately 30 with respect to the axis of the crystal, which on the graph of FIG. 3 is the O180 axis, thus indicating that a change in operating temperature of the gyromagnetic material will have substantially no effect upon the operation of the device in which the single crystal sphere of material is utilized.

The above discussion assumes, of course, that the material is operating at temperatures below its Curie temperature.

While spherically shaped specimens of gyromagnetic materials presently are preferred for use in devices of the type illustrated in FIG. 1, there are other shapes that result in the elimination of demagnetization fields. The teachings of this invention may be applied to these other shaped specimens as Well.

In practice, any known means for identifying the respective axes of the crystal may be employed. In practice, I have used the well known X-ray alignment method with considerable success. Other known methods may be employed as well, without departing from the practice of this invention, since the method of identifying and aligning the crystal form no part of my present invention.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. In an electromagnetic wave device employing magnetized gyromagnetic material whose anisotropy field is substantially stabilized against changes due to temperature changes, the combination comprising.

electromagnetic wave supporting means,

means for coupling electromagnetic waves into said wave supporting means,

a specimen of a single cubic crystal of gyromagnetic material that exhibits gyromagnetic effects to said electromagnetic waves, said specimen being subject to temperature variations,

said specimen being positioned within said wave supporting means in the path of the magnetic field of said waves and being magnetically polarized in a given direction,

said specimen being crystallographically oriented relative to said given direction to be magnetically polarized parallel to its 110 plane and at an angle of approximately 30 degrees to its 100 axis thereby to temperature stabilize said anisotropy field, whereby the electrical properties of said device are stabilized against said temperature variations.

2. The combination claimed in claim 1 wherein said specimen of gyromagnetic material is ellipsoidal in shape.

3. The combination claimed in claim 1 wherein said specimen of gyromagnetic material is a spherically shaped element.

4. The combination claimed in claim 1 wherein said specimen of gyromagnetic material is magnetically polarized parallel to its 110 plane and at an angle of 29 degrees minutes to its axis.

References Cited by the Examiner Yager et al.: Article, Ferromagnetic Resonance in Nickel Ferrite, Physical Review, vol. 8, No. 4, Nov. 15, 1950; pages 744-748 relied on.

HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

W. K. TAYLOR, P. GENSLER, Assistant Examiners.

Claims

1. IN AN ELECTROMAGNETIC WAVE DEVICE EMPLOYING MAGNETIZED GYROMAGNETIC MATERIAL WHOSE ANISOTROPY FIELD IS SUBSTANTIALLY STABILIZED AGANIST CHANGES DUE TO TEMPERATURE CHANGES, THE COMBINATION COMPRISING. ELECTROMAGNETIC WAVE SUPPORTING MEANS, MEANS FOR COUPLING ELECTROMAGNETIC WAVES INTO SAID WAVE SUPPORTING MEANS, A SPECIMEN OF A SINGLE CUBIC CRYSTAL OF GYROMAGNETIC MATERIAL THAT EXHIBITS GYROMAGNETIC EFFECTS TO SAID ELECTROMAGNETIC WAVES, SAID SPECIMEN BEING SUBJECT TO TEMPERATURE VARIATIONS, SAID SPECIMENT BEING POSITIONED WITHIN SAID WAVE SUPPORTING MEANS IN THE PATH OF THE MAGNETIC FIELD OF SAID WAVES AND BEING MAGNETICALLY POLARIZED IN A GIVEN DIRECTION, SAID SPECIMEN BEING CRYSTALLOGRAPHICALLY ORIENTED RELATIVE TO SAID GIVEN DIRECTION TO BE MAGNETICALLY POLARIZED PARALLEL TO ITS 110 PLANE AND AT AN ANGLE OF APPROXIMATELY 30 DEGREES TO ITS 100 AXIS THEREBY TO TEMPERATURE STABILIZE SAID ANISOTROPY FIELD, WHEREBY THE ELECTRICAL PROPERTIES OF SAID DEVICE ARE STABILIZED AGAINST SAID TEMPERATURE VARIATIONS.