Magneto-elastic attenuation in austenitic phase of Ni–Mn–Ga alloy investigated by ultrasonic methods

Magneto-elastic ultrasound attenuation in single crystals of a Ni–Mn–Ga is studied by ultrasonic methods at different temperatures, ranging from temperatures above the Curie point down to the vicinity of the premartensitic transition temperature. The conventional pulse–echo method is used for analysis of the attenuation of longitudinal waves only, whereas the attenuation related to shear motion is investigated by the resonant ultrasound spectroscopy (RUS). Because of the strong attenuation (increasing with the distance from the Curie point), the analysis of the resonant spectra obtained from RUS measurements must be done in successive steps, tracing individual resonances from above the Curie point into the region of higher attenuation. This method is also verified as appropriate for accurate determination of the c ′ elastic coefficient. The overall character of the attenuation is shown to be strongly anisotropic and different for longitudinal and shear waves.