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

Magnetic noises during martensitic transformations in single crystalline Ni49Fe18Ga27Co6 (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 Ni2MnGa 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 Ni2MnGa. 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. •Determination of magnetic noises during martensitic transformation in NiFeGaCo.•Micro- and nano-sized precipitates led to different noise characteristics.•Magnetic field affects the noise differently for samples with nano-precipitates.•Critical exponents were different from those obtained in Ni2MnGa single crystals.