Assessment of the magnetic entropy change in the metallic antiperovskite Mn3GaC1−δ (δ=0, 0.22)

The character of the magnetic phase transitions in the metallic antiperovskite Mn3GaC1−δ (δ=0, 0.22) was analyzed to better evaluate the associated magnetic entropy changes under various field and temperature conditions. The stoichiometric Mn3GaC compound exhibits an abrupt magnetostructural transition at T=159K that produces a large entropy change ΔSM with a plateau-like temperature dependence. A unique spike in ΔSM of Mn3GaC at T=156.5K, associated with the abrupt magnetic transformation, is attributed to the interplay between the temperature- and field-induced transitions. The peak magnitude of this entropy change spike approaches 33 J/kg K, over two times the averaged ΔSM. It was observed that the field development of ΔSM mimics the analogous magnetization behavior. An analytical phenomenological model based on the temperature and field dependence of the magnetization of this type of magnetic transition was developed to account for these results.