Magnetocaloric properties of Mn5Sn3-xGax alloys

The structural and magnetocaloric properties of Mn₅Sn_3-xGa_x alloys with x = 0.1, 0.3, 0.5, 1.0 and 1.5 are investigated. Ingots of the alloys were prepared by arc melting stoichiometric amounts of Mn (99.9%), Sn (99.9%) and Ga (99.99%) in an argon atmosphere. The ingots were annealed at 1073 K for one week in evacuated quartz ampoules, followed by quenching into water. The powder X-ray diffraction (XRD) data were collected at room temperature with Cu K_α radiation in the range of 2 θ from 20° to 80°. The results show that all alloys investigated, crystallize in the Ni₂In-type hexagonal structure with space group P63/mmc. The lattice parameters a and c decrease with increasing x. Magnetization measurements were performed in the temperature range from 5 to 400 K and in fields up to 5 T. The magnetization of the alloys initially increases with increasing temperature, and then becomes flat which is probably related to the magnetic anisotropy of the alloys. The Curie temperature of these alloys monotonously increases from 236 K for x = 0.1 to 281 K for x = 1.5. Ga substitution leads to an increase in the average moment of Mn atoms and therefore, an increase in the magnetocaloric effects, though the effects are relatively small due to the relatively small moment and the second order nature of the transition.