Premartensitic transition inNi2MnGaHeusler alloys: Acoustic emission study

Abstract

This paper deals with the study of the acoustic emission generated during the intermediate ͑premartensitic͒ transition to a micromodulated phase that precedes the martensitic transition in a nearly stoichiometric ferromagnetic Heusler Ni 52 Mn 23 Ga 25 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 ϳ2.5 kOe which is close to the field at which magnetic saturation is reached.

Investigation of the intermediate phase and magnetocaloric properties in high-pressure annealing Ni–Mn–Co–Sn alloy

“…[5][6][7]14,19 As a result, the intermediate phase transition temperature T I would decrease with increasing magnetic field. 5,16,17 As stated in the Landau expansion model, 6,14,16 F em is quasilinear with the squared magnetic moment of intermediate phase ͑M 2 ͒. Figure 3 shows T I dependence of applied magnetic field for HPA Ni-Mn-Co-Sn alloy.…”

Magnetic-Field-Induced Effects in Martensitic Heusler-Based Magnetic Shape Memory Alloys

“…The latent heat is about one-tenth of that of the martensitic transition , and anomalies in several thermodynamic quantities have been reported at the transition temperature. These are mainly in data on specific heat , internal friction , ac susceptibility (Planes et al, 1997), strain (Wu andFinlayson, 2007) and acoustic emission (Ludwig et al, 2009b).…”

An acoustic emission study of the effect of a magnetic field on the martensitic transition in Ni2MnGa

“…In order to confirm this result, we have checked that this increase in AE corresponds to a good approximation to the AE generated during isothermal rearrangement of martensitic variants under magnetic field in a zero field cooled martensitic state. 16 In summary, we have studied the AE during the martensitic transition in a Ni-Mn-Ga magnetic shape-memory alloy. Results show that nucleation and growth are influenced by the presence of a magnetic field.…”