Relaxation of twin boundaries in a Ni2MnGa single crystalline

The motion of twin boundaries in a Ni48Mn27Ga25 (at.%) single crystal has been investigated by a low-frequency mechanical relaxation spectrum analyser. A distinct internal friction peak was observed when cooling from room temperature to −70 °C at cooling rate of about 1 K/min in this single crystal with Ms temperature above 35 °C. This internal friction has been measured as a function of temperature at four frequencies: 0.1, 0.5, 1, and 5 Hz. The internal friction peaks were found to shift to high temperature with increasing frequency demonstrating a relaxation process. The activation enthalpy of the process was estimated as 0.6 eV according to the Arrhenius equation. Associated with the literature results, the underlying dynamic process was attributed to the movement of partial twin dislocations within the {1 1 2} twinning planes. Interaction between twin boundaries and defects during the movement in this magnetically induced shape memory alloy was briefly discussed.