Structural, magnetic and magnetocaloric properties of NdPrFe~(14)B and its hydrides

摘要

A systematic study of the influence of interstitial hydrogen on the structure, morphology of surface, magnetic and magnetothermal properties in multicomponent (Nd_(0.5)Pr_(0.5))_2Fe_(14)BH_x (x = 0; 2.7; 4.3) are reported. Partial substitution of Pr for Nd allows a decrease of the spin-reorientation transition temperature from 135 K for Nd_2Fe_(14)B to 73 K for (Nd_(0.5)Pr_(0.5))_2Fe_(14)B. Hydrides (Nd_(0.5)Pr_(0.5))_2Fe_(14)BH_x crystallize in a tetragonal crystal structure (space group P42/mnm) of the Nd_2Fe_(14)B-type. Both lattice constants and unit cell volume increase upon hydrogen absorption. It was also found that the surface of the hydrogenated sample was very severely damaged by the introduction of hydrogen. Magnetic studies of both initial compound and the hydrides were performed on bulk and powder samples in static and pulsed magnetic fields up to 14 and 58 T, respectively. Hydrogenation has a significant effect on magnetic properties of a multicomponent alloy (Nd_(0.5)Pr_(0.5))_2Fe_(14)B: Curie temperature and saturation magnetization increase, while temperature of SRT decreases (T_(SRT) = 63 K for (Nd_(0.5)Pr_(0.5))_2Fe_(14)BH_x with x = 2.7 and 4.3). The magnetocaloric effect (MCE) in the range of spin-reorientation transition also decreases significantly. We analyzed magnetic properties of (Nd_(0.5)Pr_(0.5))_2Fe_(14)BH_x and compare them with that of Nd_2Fe_(14)BH_x. Magnetic phase diagrams are constructed.