Spin-reorientation transitions in Nd2(Fe,Co)14B compounds and their hydrides

Magnetization and anisotropy field of Nd2Fe14-xCoxBH4.1 (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 (TSR). TSR of the initial compounds and hydrides decreases by the replacement of Fe by Co. Hydrogen insertion in the crystal lattice of Nd2Fe14-xCoxBH4.1 leads to a decrease of TSR by 15K 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 TSR decrease. The TSR 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