Spin-reorientation transitions in Nd 2(Fe,Co) 14B compounds and their hydrides

Abstract

Magnetization and anisotropy field of Nd 2Fe 14− x Co x BH 4.1 ( x=0–8) hydrides have been measured on powder aligned specimens. It was found that the unit cell volume increases after hydrogenation. At room temperature all compounds show “easy axis” anisotropy and “easy cone” anisotropy at temperatures below the spin-reorientation temperature ( T SR). T SR of the initial compounds and hydrides decreases by the replacement of Fe by Co. Hydrogen insertion in the crystal lattice of Nd 2Fe 14− x Co x BH 4.1 leads to a decrease of T SR by 15 K at Co concentrations x ⩽ 6 . The anisotropy field at room temperature decreases under hydrogenation. We can conclude that the replacement of Fe by Co causes both the unit cell volume and T SR decrease. The T SR decrease is determined by a change of electron structure and magnetocrystalline anisotropy rather than by a decrease of the unit cell volume with the Co concentration increasing.