Structural, magnetic and magnetocaloric study of Sm₂Fe_17−xNi_x (x = 0, 0.25, 0.35 and 0.5) compounds

Abstract

Magnetic refrigeration could eventually replace the conventional refrigeration, for ecological reasons and for its potential superior efficiency. Iron-rich intermetallic compounds Sm$_2$Fe$_ {17}$ are considered very interesting candidates for magnetocaloric materials because of their important magnetocaloric properties. For this purpose, three samples of $\hbox {Sm}_2\hbox {Fe}_{17-x}\hbox {Ni}_x$ ($x = 0; 0,25;0,35; 0,5$) 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 $\hbox {Th}_2\hbox {Zn}_{17}$-type structure (Space group $R\bar{3}m$). 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 $\hbox {Sm}_2\hbox {Fe}_{17-x}\hbox {Ni}_x$ exhibits a second-order ferromagnetic to paramagnetic phase transition around the Curie temperature. These curves were also used to determine the magnetic entropy change $\Delta S_M$ and the relative cooling power. For an applied field of 1.5 T, $\Delta S_M$ increases from 1.5 J/kg.K for $x=0$ 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 $\Delta S_M$ shape.