Magnetoacoustic Resonance Research Articles

The Fermi surface of antimony from magneto-acoustic resonances

Geometric resonances and deHaas-van Alphen type oscillations in ultrasonic attenuation at 150 Mc sec give a Fermi surface of antimony consisting of three electron ellipsoids tilted by 35° each containing 1.40 × 10 25 electrons m 3 and three hole ellipsoids each containing 1.46 × 10 25 holes m 3 . Comparison with available information in literature from cyclotron resonances give Fermi energies of 18 × 10 −21 J and 13 × 10 −21 J respectively.

Azbel'-Kaner Cyclotron Resonance in Gold

The results of a study of Azbel'-Kaner cyclotron resonance in gold are reported. Resonances were observed for all orientations of applied magnetic field in the (110) crystallographic plane, but identification of the observed masses with specific orbits was limited to angular regions near the principal crystallographic axes because of a relatively small experimental $\ensuremath{\omega}\ensuremath{\tau}$. Partial agreement was found between the masses observed with magnetic field parallel to principal crystallographic axes and masses obtained by Shoenberg from de Haas-van Alphen measurements. Resonances were also observed with the magnetic field tipped out of the sample surface plane at small and large angles. Differences between the effects observed at small angles and those observed by other workers in copper and silver are discussed. The resonances observed at large angles are identified with orbits. The angular ranges over which these resonances were observed provide additional confirmation of the correctness of the Fermi-surface neck dimensions established by de Haas-van Alphen and magnetoacoustic geometric resonance experiments.

Observation of Magnetoacoustic Geometric Resonances for Magnetic Field at Arbitrary Direction

Oscillations have been observed in the magnetoacoustic attenuation of Sb for sound propagated along the binary axis, and the magnetic field in the binary-bisectrix plane and the binary-trigonal plane. The oscillations were of sinusoidal, rather than of resonant character, even for $q\ensuremath{\parallel}H$, and were therefore interpreted as geometric resonances. Expressions are given for the period as a function of angle, and the data were compared with the resulting theoretical curves. Of the eight effective mass parameters necessary to evaluate the theoretical expressions, all seven of the parameters measured in a previous Shubnikov-de Haas experiment were used, and the remaining parameter was taken from the present experiment. The resulting curves are in good agreement with the data. The reciprocal effective mass tensors have been re-evaluated by using the new parameter.

The fermi surface of antimony from magnetoacoustic resonances

The fermi surface of antimony from magnetoacoustic resonances

Relation of bonding and electronic band structure to the creation of lattice vacancies in TiO

Following along the same line of approach as in a previous paper in which dissipative mechanisms were ignored, the present paper discusses the attenuation of coupled magnetoelastic oscillations in a simple deformable antiferromagnet of which the material symmetry has been broken by a relatively weak bias magnetic field. The linearized equations needed in the analysis are deduced from a fully dynamical nonlinear, rotationally invariant and thermodynamically admissible theory of deformable antiferromagnets. Three types of dissipative mechanisms are taken into account: viscosity, Spin-lattice relaxation and electrical conduction. While all these mechanisms affect to a greater or lesser degree the propagation of essentially transverse elastic modes outside resonance regions, electrical conduction modifies the absorption of spin waves due to spin-lattice relaxation and both viscosity and spin-lattice relaxation are shown to contribute, collaboratively and equally, to the damping of mixed elastic-spin modes in the two magnetoacoustic resonance regions which correspond to the interaction of left-circularly polarized transverse elastic waves and an upper spin-wave branch and right-circularly polarized transverse elastic waves and a lower spin-wave branch, respectively. The analytical discussion of the resulting dispersive and attenuated coupled modes is achieved in terms of characteristically small parameters in a quasi-magnetostatic approximation. The phenomenon of heat conduction, important as it may be, is left out of the analysis.

Spin waves in the spin-flop phase of an antiferromagnet, and metastability of the spin-flop transition

Following along the same line of approach as in a previous paper in which dissipative mechanisms were ignored, the present paper discusses the attenuation of coupled magnetoelastic oscillations in a simple deformable antiferromagnet of which the material symmetry has been broken by a relatively weak bias magnetic field. The linearized equations needed in the analysis are deduced from a fully dynamical nonlinear, rotationally invariant and thermodynamically admissible theory of deformable antiferromagnets. Three types of dissipative mechanisms are taken into account: viscosity, Spin-lattice relaxation and electrical conduction. While all these mechanisms affect to a greater or lesser degree the propagation of essentially transverse elastic modes outside resonance regions, electrical conduction modifies the absorption of spin waves due to spin-lattice relaxation and both viscosity and spin-lattice relaxation are shown to contribute, collaboratively and equally, to the damping of mixed elastic-spin modes in the two magnetoacoustic resonance regions which correspond to the interaction of left-circularly polarized transverse elastic waves and an upper spin-wave branch and right-circularly polarized transverse elastic waves and a lower spin-wave branch, respectively. The analytical discussion of the resulting dispersive and attenuated coupled modes is achieved in terms of characteristically small parameters in a quasi-magnetostatic approximation. The phenomenon of heat conduction, important as it may be, is left out of the analysis.

Magnetoacoustic Resonance in Lithium Ferrite

The parametric coupling of magnetostatic and elastic modes (magnetoacoustic resonance) has been observed in a single-crystal lithium ferrite sphere. Observation of this effect was made possible by the development of highly ordered stoichiometric lithium ferrite which has the narrowest ferromagnetic resonance linewidth of the spinel ferrimagnets [ΔH(300°K)=1.7 Oe, ΔH(134°K)=0.9 Oe at 5.4 G/sec]. The Q of the oblate-prolate elastic mode for this sphere was found to be 175 000 at 300°K. An estimate of one of the two magnetoelastic coupling constants resulted in a value B1=65×106 erg cm−3. This estimate was made by comparing the magnetoacoustic threshold for a sphere of this material with the threshold for a sphere of yttrium iron garnet (YIG), for which the coupling constants are known. A figure of merit for magnetoelastic materials is presented on the basis of which it appears that lithium ferrite may be superior to YIG in some transducer applications.

Mapping of the fermi surface by means of magneto-acoustic resonances in the amplification of sound

The quasiparticle energy spectrum of an isolated vortex in a clean layered d-wave superconductor is calculated. The Bogoliubov–de Gennes equations are solved perturbatively, within the model of step-variation of the gap function, adjusting the Caroli, de Gennes and Matricon approach for low-lying excitations in cuprates. A large peak in the density of states in a `pancake' vortex is found, as a consequence of two-dimensionality and strong coupling.

Propagation of Ultrasound in Ferromagnetic Metals at Low Temperatures

The theory of cyclotron resonance absorption of microwaves and of ultrasonic waves in ordinary metals is extended to ferromagnetic metals. First some arguments are given about the value of the force on the conduction electrons in a ferromagnet. If this force is known, the calculation of the current can be carried out in the same way as in ordinary metals. The elastic waves are coupled to the ferromagnetic resonance through the magnetostriction (magnetoacoustic resonance), and the absorption of elastic waves arises from two entirely different sources but depends in both cases essentially on the conductivity, that is, eddy currents are created by the motion of the magnetization in addition to the effects as in ordinary metals (viscosity of the electron gas, etc.). Formulas for velocity and attenuation of elastic waves are derived. For the case of microwave absorption, the surface impedance in the anomalous skin-effect region, including ferromagnetic resonance, is calculated.

THEORY OF THE PARAMETRIC OSCILLATION OF MAGNETOACOUSTIC MODES

By combining the equation of motion of a magneto-elastically coupled system derived from a classical hamiltonian and the Maxwell equations with the propagation factor neglected, we obtained a differential equation which determines the magnetic oscillations accompanying elastic vibrations of a ferrite specimen of the usual size for magnetic resonance experiments. To each normal mode of elastic vibration of the specimen there exists an associated magnetic oscillation (namely, a magneto-acoustic mode). We pointed out that the magneto-acoustic resonance phenomenon discovered by Spencer and Le Craw is a special case of the parametric oscillation involving a magnetoacoustic and a magnetostatic mode. The arrangements for observing the oscillation involving a certain magnetostatic mode and magnetoacoustic modes and the theoretical estimate of the threshold pumping power were discussed. We derived the equations coupling a magnetoacoustic and a magnetostatic mode under pumping. By analysing the (even or. odd) symmetry of the field quantities involved, we arrived at the selection rules for possible combinations of modes taking part in the parametric oscillations in a small sphere of ferrite. Finally, it was mentioned that attention should, be paid to the parametric amplification of the magnetic field accompanying thermal phonons as a possible source of noise in a ferrite microwave amplifier through the modulation of the pumping power.

Magnetoacoustic Resonance in Yttrium Iron Garnet

Additional information is given on the conditions under which magnetoacoustic resonance is observed in polished single crystal spheres of yttrium iron garnet.

Interaction of Conduction Electrons with Acoustic Phonons

The interaction of conduction electrons with acoustic phonons is studied from the general point of view. Parmenter's theory of acousto-electric effect in the high frequency range is criticized for several reasons. It is shown that Weinreich's relation between acousto-electric effect and the absorption coefficient of acoustic waves holds only in the high frequency range, and the limitation to its application is also discussed. New magneto-acoustic resonance suggested by the present author is examined qualitatively.

A proposal for determining the fermi surface by magneto-acoustic resonance

(1957). A proposal for determining the fermi surface by magneto-acoustic resonance. The Philosophical Magazine: A Journal of Theoretical Experimental and Applied Physics: Vol. 2, No. 21, pp. 1147-1148.