A new magnet material with ThMn12 structure: (Nd1−xZrx)(Fe1−yCoy)11+zTi1−zNα (α=0.6–1.3)

Abstract We previously reported a new compound for permanent magnets, (Nd 0.7 Zr 0.3 )(Fe 0.75 Co 0.25 ) 11.5 Ti 0.5 N 0.56 , which has a high saturation polarization ( J s ) of 1.68 T and a high magnetocrystalline anisotropy field ( H a ) of 2.88–4.0 MA/m. Here, we examined the effects of substituting Co and Ti at the Fe sites and Zr at the Nd sites. J s increased with Co substitution at the Fe sites, and higher Fe and Co content could be achieved by decreasing the Ti content to −Ti 0.5 . The ThMn 12 structure with high Fe and Co content (i.e. low Ti content) was stabilized mainly by −Zr 0.3 substitution at the Nd sites. The Zr substitution resolves the local mismatch in atomic size in the structure. Specifically, the atomic radius of Zr is about 88% that of Nd, so the local structure surrounding Nd (2a site) shrinks as a result of the substitution and resolves the size mismatch in the three types of local Fe six-fold symmetric hexagons in the structure. The effect of the α-(Fe, Co) phase on J s was evaluated from the phase's volume fraction measurement of 7.7% (8.1 wt%) by electron backscatter diffraction. Nitrogenation of the starting alloy also resulted in augmentation of the c -axis magnetocrystalline anisotropy. Finally, we confirmed a high J s (−N 1.3 ) of 1.71 T (=1.67 T, −0.04 T for the α-(Fe, Co) phase) and H a of 2.9–5.25 MA/m ( H a (−N 1.3 )=5.25 MA/m) in the (Nd 0.7 Zr 0.3 )(Fe 0.75 Co 0.25 ) 11.5 Ti 0.5 N α ( α =0.60–1.30) compounds.