Vibrational and magnetic behavior of transforming and nontransforming Ni-Mn-Ga alloys

Temperature dependences of the vibrational and magnetic properties of the high symmetry parent phase in three different alloys Ni51.1Mn24.9Ga24.0, Ni49.7Mn24.1Ga26.2, and Ni49.6Mn21.9Ga28.5 are measured in the temperature range between 4.2 and 3000.3em0exK. While in the first two alloys an intermediate transformation precedes the subsequent martensitic transformation (MT), the MT is not detected in the analyzed temperature range in the third one. The features of both the intermediate phase transformation and the intermediate phase in these alloys are determined. It is found that the elastic characteristics of the high symmetry phase are similar independent of the closeness of the martensitic transformation. Besides, the magnetic susceptibility shows also a similar behavior in the parent phase of the three alloys, while in the intermediate phase, this behavior differs in the nontransforming alloy. In the latter case, the susceptibility shows an anomalous increasing during cooling down to 4.20.3em0exK. The continuous increase of the resonance frequency measured by resonant ultrasound spectroscopy and the anomalous increase of the magnetic susceptibility during cooling must be an intrinsic characteristic of the intermediate phase with no obvious relationship to the appearance of the martensitic transformation.