Abstract
Abstract Using two complementary ultrasonic methods the complete set of elastic constants of the austenite phase of Ni Mn Ga ferromagnetic shape memory alloy was measured in magnetic field up to saturation and in temperature range 295–400 K. While the coefficients c 11 and c 44 were nearly independent of the field and the temperature, the shear coefficient c ′ increased strongly with increasing field and temperature. Experiment indicates that two independent mechanisms contribute to the anomalous shear softening of the c ′ coefficient in Ni Mn Ga austenite; the structural softening of the bcc lattice and the softening due to magneto-elastic coupling. Above the Curie point and in the saturation field only the structural softening took place with rate about 10 MPa/K. In the demagnetized state the combined softening was approximately 35 MPa/K. Similar dependencies on the temperature and the magnetic field were also observed for the ultrasound attenuation of the shear mode.
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