Structural, magnetic and magnetocaloric study of Sm2Fe17-xNix (x=0, 0.25, 0.35 and 0.5) compounds

Magnetic refrigeration could eventually replace the conventional refrigeration, for ecological reasons and for its potential superior efficiency. Iron-rich intermetallic compounds Sm2Fe17 are considered very interesting candidates for magnetocaloric materials because of their important magnetocaloric properties. For this purpose, three samples of Sm2Fe17-xNix (x=0;0,25;0,35;0,5) were prepared by arc melting and subsequent annealing at 1073 K for a 7 days. Structural analysis by Rietveld method on X-ray diffraction (XRD) has determined that these alloys crystallize in the rhombohedral Th2Zn17-type structure (Space group R3<overbar></mml:mover>m). Measurements of the magnetic properties revealed that the Curie temperature increases, while the unit cell parameters decrease. For each sample, the isothermal magnetization curves have been measured, for different temperatures in the vicinity of the Curie temperature, with an applied field up to 1.5 T. Based on the Arrott plot, these analyses show that Sm2Fe17-xNix exhibits a second-order ferromagnetic to paramagnetic phase transition around the Curie temperature. These curves were also used to determine the magnetic entropy change Delta SM and the relative cooling power. For an applied field of 1.5 T, Delta SM increases from 1.5 J/kg.K for x<mml:mo>=0 to 4.9 J/kgK for x = 0,5. In addition, the RCP increases monotonously. This is due to an important temperature range for the magnetic phase transition, contributing to a large Delta SM shape.