Reflection and refraction of acoustic waves at the boundary between a Heusler ferromagnetic alloy and dielectric

Reflection and refraction of longitudinal and transverse acoustic waves at a planar boundary between a dielectric and a ferromagnetic Heusler alloy Ni2+x+yMn1−xGa1−y in the range of premartensitic and martensitic phase transitions is considered. We show the possibility of efficiently controlling the angles of reflection and refraction of both longitudinal and, especially, transverse waves, as well as all four coefficients of conversion of the wave type, by the variation of temperature which induces strong anisotropy of elastic properties of the crystal. Conditions for the appearance of critical angles and accompanying surface vibrations as well as for total reflection are discussed. The possibility is analyzed of emission of the arising wave gliding along the interface between the two media into the bulk of the material with the development of a new complex damped dissipationless wave process in the vicinity of the phase transition. Based on Trivisonno’s experimental data on the temperature dependences of the sound velocity in an Ni2MnGa single crystal, the conclusions of the theory developed are illustrated by numerical calculations for a concrete Ni2MnGa-quartz structure.