Influence of nanocrystallization on the magnetocaloric properties of Ni-based amorphous alloys: Determination of critical exponents in multiphase systems

Traditionally the study of the magnetocaloric effect (MCE) in amorphous and nanocrystalline alloys has been focused on Fe and rare earth based compositions. However, they present problems that hinder their application such as the high price of rare earths or the necessary addition of a large fraction of non-magnetic elements in Fe-based alloys in order to tune their response to temperatures close to room temperature. Alternatively, Ni-based amorphous alloys have the Curie temperature (TC) well below room temperature and with a good glass forming ability. For these alloys, Fe addition provides a good tool to tune TC close to room temperature. In this work, the magnetocaloric properties of Ni82−xFexSi2B16 (x = 8, 12, 13.2, 16) have been studied in the amorphous and nanocrystalline state. Besides compositional dependence of MCE in this series, a detailed analysis of the critical exponents of the magnetic transition of both amorphous and nanocrystalline alloys has been performed using the magnetic field dependence of MCE. Results were compared with those derived from the Kouvel-Fisher method, requiring a deconvolution of the different magnetization contributions in the Kouvel-Fisher case for nanocrystalline alloys.