Spin reorientation and magnetohistory of DyFe12-xNbx compounds

Structural and magnetic properties, especially the magnetocrystalline aniso tropy of DyFe12-xNbx compounds with x = 0.55-0.85, have been investigated. The easy magnetization directions at room temperature for all the compounds are along the c-axis. With decreasing temperature the magnetocrystalline a nisotropy changes from easy axis to easy cone at T-sr2, then to easy plane at T-sr1. A spin phase diagram has been constructed for DyFe12-xNbx. The ch ange of magnetocrystalline anisotropy was further investigated by the angul ar dependence of magnetization with respect to the magnetic field at variou s temperatures. The temperature dependence of the cone angle was determined for DyFe11.3Nb0.7. It is noteworthy that with increasing Nb content both T -sr1 and T-sr2 decrease monotonically while the Curie temperature is almost independent of Nb content. The cone angle increases monotonically with dec reasing temperature from T-sr2 and discontinuously comes up to 90 degrees a t T-srl. The temperature dependence of the cone angle can be quite well def ined in terms of crystal field theory. In addition, an obvious magnetohisto ry effect was observed for all compounds at low temperature. The critical f ield of magnetohistory was found to be smaller than 0.5 T for DyF11.3Nb0.7.