Magnetic noises emitted during martensitic transformation in Ni49Fe18Ga27Co6 single crystalline shape memory alloys

Abstract Magnetic noises during martensitic transformations in single crystalline Ni 49 Fe 18 Ga 27 Co 6 (at. %) alloys were measured. The critical exponents of the acoustic and magnetic noises were slightly different from each other in contrast to those obtained in Ni 2 MnGa single crystals, measured so far. The presence of nano-sized γ-particles increased the noise activity and resulted in bipolar magnetic noise, in contrast to mostly unipolar signals observed in the homogeneous sample or in Ni 2 MnGa. Application of a moderate external magnetic field (20.9 mT) decreased the bipolar nature of the noise, which was qualitatively explained by the magnetoelastic coupling and by the more ordered magnetic domain structure. Nano-sized precipitates resulted in more fine steps of the jerky motion of the interface and caused barriers against of the easy development of the magnetic structure.