Electronic structures and related properties of Ce2Fe17-based magnetocaloric material upon Nd/Si substitution

Abstract

The electronic structures and magnetocaloric properties of Ce2Fe17-based materials doped with Nd/Si have been investigated by means of experiments and first-principles calculations based on density functional theory (DFT). Ce1.6Nd0.4Fe17−xSix alloys crystallize in a rhombohedral Th2Zn17-type 2:17R main structure with trace amounts of the α-Fe secondary phase, and Si substitution for Fe contributes to the 2:17R phase. Compared with the parent Ce2Fe17 compound, Nd/Si substitution increases the Curie temperature (TC) to 273 K for Ce1.6Nd0.4Fe17 and to 297 K for Ce1.6Nd0.4Fe16.67Si0.33. DFT calculations reveal that Nd/Si addition increases the c/a values and Fe-Fe interatomic distances at the 6c site, thus leading to an enhanced TC. In addition, Si atoms in Ce2Fe17-based alloys energetically prefer to occupy the 18h site. The local density of states and charge density difference map for a single Si and its first-nearest-neighbor Fe atoms confirm a strong hybridization between the electronic orbitals of Si and Fe atoms, leading to slight lattice contraction and a decrease in the formation energy of the 2:17R phase. The Ce1.6Nd0.4Fe17−xSix alloys exhibit a maximum isothermal magnetic entropy change (ΔSM) of 3.7–4.1 J/kg K, working temperature range (∆TFWHM) of 90.5–95.5 K, and a relative cooling power (RCP) of 350–371 J/kg at μ0∆H = 5 T, suggesting that Nd/Si substitution contributes to the optimization of Ce2Fe17-based alloys as potential room-temperature magnetic refrigerants.