Abstract

Calculation of Magnetoacoustic Echo Signals in Ferrite Powders

S.N.Karpachev (Faculty of Physics, Moscow State University, Moscow, Russia); V.S.Vlasov, L.N.Kotov (Department of Radiophysics and Electronics, Faculty of Physics, Syktyvkar State University, Syktyvkar, Russia)

e-mail: snk@snk.phys.msu.su

The phenomenon of magnetoacoustic echo (MAE) in ferrite powders is investigated. The main point of it is generation of extra RF pulses after the powder excitation by a sequence of two powerful RF pulses. The echo signal amplitude of a ferrite powder is obtained on the basis of Landau-Lifshitz equation and the equation for the mechanical displacement vector. To simplify the solving of the problem, the following approaches are made: the system consisting of single-domain particles having a thin disc-shape and elastic oscillation of the particles are taken into account only along one direction. Analytical expression, describing MAE signals, is obtained for small amplitudes of the exciting impulses of the variable magnetic field. Interaction among powder particles is ignored. The method of numeric solving of the equation system above mentioned is taken for the case of large amplitudes of the exciting pulses and for the most precise calculation of MAE signal-echoes in the case of small amplitudes of the exciting impulses. The data obtained in the paper are compared with the existing experimental data.

Section : 2