Abstract

Electromagnetic Generation of High Harmonics of Ultrasound in Magnets

R.Il'yasov, S.E.Babkin, M.Yu.Glavatskikh (Physical-Technical Institute, Ural Division of RAS, Izhevsk, Russia)

e-mail: emp@fti.udm.ru

The propagation of ultrasound in magnetoelastic materials is accompanied by generation of high harmonics due to elastic nonlinearity and effective anharmonicity of coupled acoustic and spin waves. Anharmonicity of the direct electromagnetic-acoustic conversion (EMAC) plays a most essential role in the electromagnetic generation of ultrasound. This mechanism is caused by the non-linearity of magnetoelastic interaction and results in the appearance of high harmonics along with the basic frequency during immediate action of the electromagnetic field on the magnet in the skin-layer. In the present work, the regularities of nonlinear EMAC for different types of elastic waves are studied both theoretically and experimentally. The generation of all harmonics of longitudinal and Rayleigh (or Lamb) waves is shown to be allowed. In contrast, generation of even harmonics of the transverse waves propagating normally to the surface, as well as of the SH waves in plates is impossible. The generation of high harmonics of surface acoustic waves is caused by the appearance of elastic deformations synchronized in space and time in magnet. The efficiencies of generation of even and odd harmonics depend differently on the magnetic state of the sample. The ultrasound generation at high harmonics near the Curie point and in the range of both spontaneous and magnetic field-induced spin-reorientation phase transitions for different ferromagnets is experimentally studied. The increase in generation efficiency near the magnetic phase transition turns out to be greater at high harmonics than at the basic harmonic.

Section : 2