Hypersound spin-wave resonances in strained crystal of iron borate

Abstract

Antiferromagnets (AF) and simultaneously “weak” ferromagnets with anisotropy of the “easy plane” tape, such as hematite (a-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and iron borate (FeBO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), possessesa number of the unique characteristics. Their high Neel's temperature and a tremendous effective uniform exchange fieldresult in a strong magnetoelastic (ME) coupling. Due to above reasons, the peculiarities of dynamic effects of ME coupling in the iron borate present a physical interest, as the dynamic and static elastic deformations can change the magnetic properties of the crystal.In the direction of longitudinal sound propagation q ∥ C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ( q - is the sound wave vector, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> - is the threefold axis normal to the {111} basal “easy plane” of crystal)the ME coupling is due to a piezomagnetic (PM) mechanism [1], and a magnetostriction coupling between the longitudinal elastic oscillations along C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and magnetic subsystem is negligibly small due to a large energy gap for the high-frequency branch of spin-wave spectrum.At propagation of longitudinal hypersound wave along the axis of symmetry C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> of FeBO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal in the magnetic field, the oscillation structures (OS) of amplitude and phase of a transmission coefficienthave been found out, and the physical model of that phenomenon was offered by us [2]. The idea is that in the mode of standing sound wave, a magnetic modulation (incommensurable) structure (MMS) there can be in a sample. In present work the frequency dependence of the resonances observed is experimentally investigated in the external magnetic field and their numerical simulation is conducted.