US3087122A - Electromagnetic wave generation utilizing electron spins in magnetic materials - Google Patents

Electromagnetic wave generation utilizing electron spins in magnetic materials Download PDF

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Publication number
US3087122A
US3087122A US68413A US6841360A US3087122A US 3087122 A US3087122 A US 3087122A US 68413 A US68413 A US 68413A US 6841360 A US6841360 A US 6841360A US 3087122 A US3087122 A US 3087122A
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energy
field
pressure
frequency
materials
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US68413A
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John H Rowen
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to US68413A priority Critical patent/US3087122A/en
Priority to DE19611416470 priority patent/DE1416470B2/de
Priority to SE10615/61A priority patent/SE301500B/xx
Priority to BE609914A priority patent/BE609914A/fr
Priority to GB39934/61A priority patent/GB949645A/en
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/26—Automatic control of frequency or phase; Synchronisation using energy levels of molecules, atoms, or subatomic particles as a frequency reference
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F7/00—Parametric amplifiers
    • H03F7/02—Parametric amplifiers using variable-inductance element; using variable-permeability element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
    • H03K3/78—Generating a single train of pulses having a predetermined pattern, e.g. a predetermined number

Definitions

  • This invention relates to methods and means for electromagnetic wave generation, and more particularly, to the production of either pulses or continuous radiation of high frequency wave energy in the microwave and millimeter wave range by direct conversion of low frequency, ultrasonic acoustical energy into high frequency radio energy.
  • a physical or mechanical distorting pressure applied to an anisotropic material will alter the magnetocrystalline anisotropy energy of the material. Since the crystalline energy implies an equivalent magnetic field equal to the second derivative of the energy with respect to orientation, the effect on the magnetic spins is substantially identical to the effect of altering the external magnetic field. Particularly, a distorting pressure will alter either the direct-ion or magnitude or both of the effective internal magnetic field of the material determined by the magnetocrystalline energy, even though the external field remains unchanged. It will be recalled that an anisotropic mate- "Ice rial is one having magnetic properties that are different in different directions so that the magnetization tends to be directed along certain definite crystallographic axes.
  • the principles of the invention may be practiced with any material that shows strong magnetostrictive effects, that is, a change in the magnetocrystalline structure of the materials and its internal magnetic energy with deformation even though the material is not ordinarily considered as gyromagnetic.
  • the total magnetocrystalline energy of the spin system of all crystalline solids containing atoms having uncompensated spins is made up of the sum of three components: the energy due to spin-orbit interaction, the energy due to dipole-dipole interaction, and the energy of exchange interaction between neighboring spins.
  • the exchange energy is small while the dipole-dipole energy and/ or the spin-orbit energy are significant in causing so-called zero-field-sp-litting or magnetic anisotropy.
  • the exchange energy is also large, and its effect is to produce either parallel or antiparallel alignment of the spins of neighboring atoms. In the case of ferromagnetic and ferrimagnetic materials this gives rise to a large magnetic moment due to the spins of many atoms acting in concert while in antiferromagnetic materials the spins are divided into two equal anti parallel sublattices whose magnetic moments just neutralize each other so that the material has no appreciable external magnetic moment.
  • the dipole-dipole energy and/ or the spin-orbit energy determine the anisotropy energy and the specific crystallographic directions along which the spins of one or more sublattices prefer to lie.
  • the exchange energy determines the extent to which the spins of neighboring atoms tend to remain aligned (parallel or antiparallel) with each other.
  • the resonance frequency of the material in the following way.
  • all spins act in concert at a resonance frequency proportional to a magnetic field function, designated the internal effective field H which essentially comprises the vector sum of the external biasing field and the anisotropy field.
  • the mode of resonance is characterized by one of the sublattices moving with respect to other, and so the effective field H is expressed by a function to be set out hereinafter which includes a term representing also the exchange energy field.
  • This exchange field is so large that the contribution of the externally applied field to the resonance frequency is small and, therefore, the external field is not essential to produce resonance at high microwave frequencies in anti-ferromagnetic materials.
  • the pressure is applied along the hard axis of magnetization of a sample that is biased by a static magnetic field at an acute angle to the easy axis.
  • the pressure produces a shift in the position of the anisotropy field and, therefore, a shift in the position of the total magnetic moment of the mation with respect to pressure;
  • Electron precession from the original position to the new position of the moment will produce radiation alignment during the transit period following, thcede formation as the sublattices returnto equilibrium with their surroundings and will radiate electromagnetlc wave energy at the antiferromagnetic resonance frequency during this period. This radiation takes place whether or not the material is biased by an externalfield.
  • the resulting microwave energy fromjeitheremb'odiw f ment constitutes a primary source of energy useful for pumping masers and parametric tamplifiers,lfor use in high resolution radar systems, or for any other application requiring simply generated high frequency energy.
  • FIG. 1 is a schematic showing of an illustrative embodiment of the invention utilizing the properties of ferromagnetic, ferrimagnetic or paramagnetic. materials;
  • FIG. 1A is a representation of the crystal structure of a preferred cubic material for use in the embodiment of FIG. 1;
  • FIG. 2 is a polar plot of a typical anisotropy energy surface given for the purpose of explanation
  • FIG. 5' is a schematic showingof an illustrativeernr-,.
  • FIG. 5A is a representation of a crystal of a preferred material having a tctragonal structure for use in the em bodiment of FIG. 5.
  • Sphere 11 represents the active element of material which is mechanically connected to an ultrasonic transducer 12.
  • emodimcnt sphere 21 may be made of any of the several non-conductive, high anisotropy magnetic materials exhibiting pronounced piezomagnetic' effects and aiso gyromagnetic effects atrnicrowave frequencies and;
  • it may be one of the cubic ferrim'agnctic spinels such as single crystal. ferrite, a ferrimagused to practice the invention. to understand that theganisotropy. ,energy of a fcrro-.
  • T The size of sphereli is such thatv it'is mechanically resonant to the ultrasonic pressure] waves andso depends uponthe frequency of the pres sure, waves and their wavelength within the particular material.
  • an yttrium I iron garnet sphere of approximately fifteen milsin diameter is resonantat approximately ten rnegacycles. Such a resonance intensifies the pressure variations upon the crystal lattice of the material.
  • transducer 12 comprises a segment 13 of barium titanate shaped as a circular segment of a spherical shell. The ultransonic frequency generated by transducer 12 is determined by the resonant thickness of segment 13.
  • Electrodes 14 and 15 are connected to the conductors of the coaxial line 16 which, in turn, is connected to an electrical source 17 of wave energy of ultrasonic frequency.
  • transducer 12 further includes a focusing member 19 which makcsthe mechanical connection between seg meat 13 andsphere 11.
  • member 19 takes'the form of a cone of dense dielectric material, such as fused silica or quartz, having aspherical base surface that mates with andissuitably bonded to electrode 14.- The oppositeend is slightly truncated to mate with sphere 11. it is ofparticularimportance that sphere 11 be oriented withits axis of hard magnetization aligned with the direction'ot' pressure for the;
  • 1A illustrates the crystal structure and the conventionally designated axes for the particular case of cubic yttrium iron garnet.
  • the cube edges are designated the [100], [010] and [001] axes and are the directions of hard magnetization.
  • the body diagonals are designated [111] and equivalent axes and are the easy directions.
  • the coupling may comprise -a coaxial conductor 21 which terminates in a small loop 22 in close proximity to element 11. Since the time varying component of the flux exists substantially normal to the biasing field, the plane of loop 22 is substantially parallel to the biasing field H The size of loop 22 and its spacing from element 11 are such as to produce a condition of tight coupling. For this condition the radiation damping is approximately equal to the spin-lattice damping and corresponds to a perfect match between the electromagnetic structure and the spherical sample at ferromagnetic resonance. This affords the maximum transfer of energy to the useful load represented by 23 which is connected to the other end of coax 21.
  • sphere 11, loop 22 and all or part of transducer 12 may be included in a conductive shield which may or may not play a part in the coupling between loop 22 and sphere 11.
  • this shield takes the form of a resonant cavity, which itself provides the coupling means to receive the generated energy.
  • the solid curve 31 represents a polar plot of the anisotropy energy surface of a cubic crystal in its unstressed condition.
  • the hard axis of magnetization represented by [100] has the largest anisotropy energy.
  • the easy axis represented by [111] has the smallest anisotropy energy.
  • the anisotropy energy along the axis [111] can be represented approximately by a magnetic field of magnitude K /M where a K is the first term of the anisotropy constant and M is the magnetization.
  • the total effective field H within the material is the vector sum of H and K /M and may be represented on FIG. 2 by the vector H between H and K /M.
  • FIG. 3 The Way this shift in the easy direction of magnetization takes place is shown in FIG. 3 by the plot of the angle of the easy direction from an arbitrary reference versus the pressure applied. The curve indicates that for pressures below the pressure designated P the direction of the easy magnetization is not changed. At the pressure P the angle begins to increase rapidly to reach its maximum at P for which the easy axis is now substantially aligned with the direction of pressure.
  • the frequency of this pressure wave will be in the ultrasonic range and of the order of ten megacycles.
  • the change in orientation of the easy axis will take place at approximately 10* seconds. Since materials such as single crystals of yttrium iron garnet have relaxation times as long as l0 seconds, the precessional motion produced during each interval of rapidly changing internal field will persist substantially 'undiminished until the next cycle of the ultrasonic wave reinforces the precession. Thus, a continuous radiation of microwave energy is produced.
  • the precessional motion has a selectable frequency within a broad range in the microwave and millimeter wave bands, that is, a frequency of several thousand megacycles and higher.
  • FIG. 4 illustrates one of the many possible ways in which the principles of the invent-ion may be applied to a physical waveguide embodiment and also illustrates the important principle of static pressure biasing.
  • Reference to FIG. 3 above will indicate that valuable time and exciting energy is expended in the embodiment of FIG. 1 in varying the pressure through the region from zero to the pressure P It is thus proposed to pressure bias the sample with a static pressure just below the pressure P Thus, the required excursion of variable pressure is substantially reduced.
  • FIG. 4 static pressure is applied by backing sphere 11 with a plate 40 of dielectric material.
  • a section 41 of conductively bounded waveguide of circular crosssection is employed.
  • the right end of guide 41 is connected to the utilizing load and the left end thereof contains the ultrasonic transducer 12. Since transducer 12 may be identical to the one described with reference to FIG. 1, corresponding reference numerals have been emapplied at an angle as described above.
  • the cavity is excited by sphere 11 in a more or less circularly polarized mode.
  • paramagnetic materials have known gyromagnetic ratios and known relaxation times with respect to whichthe preceding analysis can be applied. While they are not usually thought of as having hard and easy directions of magnetization they do have known directions along which the application of pressure will alter the energy level distribution which, for the purposes of the present invention, is equivalent to altering the direction of easy magnetization.
  • a particular example of a suitable paramagnetic material is cerium ethyl sulfate, known to have a large zero-fieldsplitting for small distortions.
  • FIG. 5 The case of antifetromagnetic materials is slightly different and thewmodifications necessary to employ this material are illustrated in FIG. 5. Since the details of the ultrasonic transducer 12 are identical to those employed in FIG. 1, conresponding reference numerals have been used to identify corresponding components. Referring to FIG. 5, modification will be seen to reside in the orientation of sample 51 of antiferromagnetic material, the absence of a'biasing magneticfield, andthe orientation of the pick-up loop 53. Specifically, sample 51 is orientated so that the known antiparallel direction oii the particular material is at some angle to the direction of pressure from transducer 12.
  • the antipar'alleldireo tion is that defined above as the direction along which the individual sublattices of the particular material prefer to be aligned in the orientation typical of antiferromagnetic materials.
  • the optimum angle between. the axis 7 of pressure and the antiparallel direction cannot be gen eralized for all materials since it depends upon the crystal symmetry of the particular material employed.
  • a preferred example of antiferromagnetic material is cobalt fluoride and the tetragonal crystal structure of this mia tcrial as shown in FIG.
  • the antiparallel axis 52 is the [001] and [001] axes with the oppositely directed vectors designating the antiparallel alignment of the two sublattices. For this particular material (and others of similar crystal symmetry) pressure applied along.
  • the resonance frequency may be modified by the presence of an external biasing field H directed along the antiparallel [001] axis in which case it adds or. subtracts from the crystalline field as. shown in the equation.
  • the wave generator according to claim 1 including means for applying a steady external magnetic field to said body
  • said body being of ferromagnetic material for which said internal effective field comprises substantially the vector sum of said anisotropy field of said material and said external field.
  • a generator of high frequency wave energy comprising a body of material having an anisotropy crystalline field that varies with deformation of the material and an electron system that will precess in response to changes in said field,
  • means including an ultrasonic transducer for applying a deforming physical pressure to said body that varies at an ultrasonic rate
  • a source of high frequency wave energy comprising an element of material having magnetic properties that are changed by the application of stress to the material
  • said means coupled to said element comprises a coupling loop having the plane thereof extending parallel to the direction of said applied field.
  • said means coupled to said element comprises a resonator including a conductively bounded cavity surrounding said element.
  • a source of high frequency wave energy compris- 2 an element of magnetic material having easy and hard axes of magnetization that are changed by the application of stress to the material, means for applying a magnetic field to said element at an acute angle to said easy axis, means for applying periodic pressure to said element along said hard axis, and means coupled to said element for receiving electromagnetic wave energy radiated by said element.
  • said element is a sphere of yttrium iron garnet.
  • a source of high frequency wave energy compris- No references cited.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
  • Gyroscopes (AREA)
  • Hall/Mr Elements (AREA)
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US68413A 1960-11-10 1960-11-10 Electromagnetic wave generation utilizing electron spins in magnetic materials Expired - Lifetime US3087122A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US68413A US3087122A (en) 1960-11-10 1960-11-10 Electromagnetic wave generation utilizing electron spins in magnetic materials
DE19611416470 DE1416470B2 (de) 1960-11-10 1961-10-24 Generator für hochfrequente Schwingungsenergie mit einem Körper aus einem ein magnetokristallines Feld aufweisenden Material
SE10615/61A SE301500B (enrdf_load_stackoverflow) 1960-11-10 1961-10-25
BE609914A BE609914A (fr) 1960-11-10 1961-11-03 Procédé et moyen pour engendrer des ondes électromagnétiques
GB39934/61A GB949645A (en) 1960-11-10 1961-11-08 Improvements in or relating to generators of high frequency wave energy

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US68413A US3087122A (en) 1960-11-10 1960-11-10 Electromagnetic wave generation utilizing electron spins in magnetic materials

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BE (1) BE609914A (enrdf_load_stackoverflow)
DE (1) DE1416470B2 (enrdf_load_stackoverflow)
GB (1) GB949645A (enrdf_load_stackoverflow)
SE (1) SE301500B (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3235819A (en) * 1962-04-02 1966-02-15 Gen Precision Inc Microwave modulator using single crystal ferrite
US3252111A (en) * 1962-04-24 1966-05-17 Varian Associates Pulsed ferromagnetic microwave generator
US3398383A (en) * 1965-07-28 1968-08-20 Air Force Usa Microwave modulator using anisotropic effects of ferromagnetic resonance in single crystals
US3409823A (en) * 1966-07-01 1968-11-05 Air Force Usa Method of eliminating magnetocrystalline anistropy effect on spin resonance of ferrimagnetic materials
US3441837A (en) * 1964-03-12 1969-04-29 Thomson Houston Cie Franc Gyromagnetic resonance magnetometer with ferrimagnetic sample

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2944255A1 (fr) 2009-04-10 2010-10-15 Stx France Cruise Sa Module de production d'energie pour un navire et ensemble de navire associe

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3235819A (en) * 1962-04-02 1966-02-15 Gen Precision Inc Microwave modulator using single crystal ferrite
US3252111A (en) * 1962-04-24 1966-05-17 Varian Associates Pulsed ferromagnetic microwave generator
US3441837A (en) * 1964-03-12 1969-04-29 Thomson Houston Cie Franc Gyromagnetic resonance magnetometer with ferrimagnetic sample
US3398383A (en) * 1965-07-28 1968-08-20 Air Force Usa Microwave modulator using anisotropic effects of ferromagnetic resonance in single crystals
US3409823A (en) * 1966-07-01 1968-11-05 Air Force Usa Method of eliminating magnetocrystalline anistropy effect on spin resonance of ferrimagnetic materials

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DE1416470A1 (de) 1969-02-06
BE609914A (fr) 1962-03-01
SE301500B (enrdf_load_stackoverflow) 1968-06-10
GB949645A (en) 1964-02-19
DE1416470B2 (de) 1970-08-06

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