Optimizing the intrinsic magnetic properties of REFe_12-xM_xphases

Collecting energy from renewable resources, using e.g. wind power plants has become important and goes hand in hand with a growing demand for new permanent magnets (PM) with magnetic performance comparable to Nd-Fe-B magnets. A key task is to identify new PM with less rare earth (RE). Systems with ThMn₁₂ structure are of special interest. They have the lowest RE concentration of all known phases. However, Fe-based 1:12 systems with light RE need a phase stabilizer which goes on the Fe sites.
Two types have been studied, (Nd_1-xY_x)Fe_12-yTi_y and SmFe_12-yV_y, using state of the art density functional theory methods (VASP; FP LMTO RSPt). The phase stability and the magnetic properties were calculated depending on the Ti and V concentration. Aiming to reduce the RE amount the performance depending on the Nd/Y ratio was monitored.
We find that the Nd-Y (Sm) system is stable down to y = 0.5 (y=1) which leads to an increase of the magnetization by 17% compared to the commonly used concentrations of Ti (V). In viev of the MAE a replacement of Nd by Y turned out to be preferable over a reduction of Ti. MAE values of 1.3 MJ/m³ ((NdY)Fe₁₁Ti) and 1.7 MJ/m³ (SmFe₁₁V) are predicted. The latter could be verified in recent experiments.