Magnetocaloric Properties of MnBi Compound as a Function of Grain Size

MnBi is a magnetic material with many peculiar properties, interesting for different applications such as rare-earth-free permanent magnets and magnetic refrigeration. In this work the entropy change and the transformation kinetics of the magneto-structural transition are investigated, for two sets of samples with different grain size (“as-annealed” and “compacted pwd”). Both sets show a logarithm dependence on the temperature scan rate of the transition temperature upon cooling. This suggests that thermal activation effects are present. The estimated activation volume v0 of the magneto-structural transition corresponds to around 120 atoms.