Effect of Ga and Nb addition on the magnetic properties of the Nd 2(Fe, Co) 14B compound

Abstract

The Curie temperature, saturation magnetization and ac-susceptibility of Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B compounds in the concentration range O⩽ x⩽0.2 and O⩽ y⩽0.3 are determined. The Curie temperature of the compounds lying in the single phase region is approximately 480°C irrespective of the variation of Ga(Nb) content. Both room temperature saturation magnetization and spin reorientation temperature determined by ac-susceptibility measurements between 70 and 300 K were found to decrease with increasing Ga(Nb) concentration. Room temperature anisotropy field of single phase Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B decreases with increasing Nb content when Ga is kept constant, whereas when the Nb-content is constant it increases first with increasing Ga, and decreases again after reaching a maximum. The results of temperature dependence of anisotropy field of Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B series show that the effect of addition of Ga(Nb) on the anisotropy field is different in different temperature ranges. It is thought that different Fe crystallographic sites of the 3d- sublattice of Nd 2Fe 14B type structure may contribute differently to the anisotropy field and that the temperature dependence of the anisotropy field indicates that the contribution to anisotropy field from a specific Fe site is different at different temperatures.