The influence of processing, composition and temperature on the magnetic characteristics of nanophase RE-Fe-B alloys

The effects of Pr:Nd and RE:Fe (RE=Rare Earth) ratios, Co substitution for Fe and of mean crystallite size dg on the spin reorientation temperature Tsr of the RE2Fe14B phase have been systematically investigated. Increasing Pr:Nd and Co:Fe ratios and reduction in dg result in reduced Tsr, owing to inter-grain exchange coupling, while changes in the RE:Fe ratio, surprisingly, have no significant effect on Tsr. The elevated temperature magnetic properties of nanocrystalline REFeB alloys have also been studied as functions of Nd:Pr, RE:Fe and Fe:Co ratios. The influence of these factors and of dg on the temperature coefficients of both the remanence Jr and the coercivity jHc are discussed in the context of optimizing the thermal stability with respect to both reversible and irreversible losses. Nanocomposite alloys have lower coefficients of Jr than single-phase and RE-rich counterparts, owing to exchange coupling effects, while Co substitution for Fe has the largest effect in decreasing the coefficients for both Jr and iHc. On the other hand increasing Pr:Nd has little effect on either coefficient.