Premartensitic transition in Ni2MnGa Heusler alloys: Acoustic emission study

This paper deals with the study of the acoustic emission generated during the intermediate (premartensitic) transition to a micromodulated phase that precedes the martensitic transition in a nearly stoichiometric ferromagnetic Heusler Ni52Mn23Ga25 crystal under applied magnetic fields. In the range of applied fields, the field stabilizes the high-temperature cubic phase by shifting the transition to lower temperatures. At low fields the amplitude, energy, and duration distributions of the acoustic emission events show power-law behavior which reflect the absence of characteristic scales associated with the transition. The corresponding exponents increase with the applied field, which indicate a weakening of the first-order character of the transition. No acoustic emission has been detected above similar to 2.5 kOe which is close to the field at which magnetic saturation is reached.