Microstructures and magnetic domain configurations of NdFe11Ti and Nd2(Fe,Ti)17 aggregates

Abstract

Nd:11Fe:Ti alloys produced by arc melting and splat quenching have been investigated by scanning electron microscopy, transmission electron microscopy, magnetic force microscopy and magnetic measurements. Both the as-cast and splat-quenched materials crystallized adopting essentially the ThMn12-type structure. However, the RFe11M (where R is a rare-earth element and M is an early 3d element or other non-magnetic element) stoichiometry was not strictly followed and α-Fe(Ti) and Nd2(Fe,Ti)17 could be detected in the microstructures. Magnetic force microscopy showed that the critical size for single-domain behavior in the splat-quenched aggregates was close to 100 nm. Annealing treatments induced a NdFe11Ti → Nd2(Fe,Ti)17+α-Fe(Ti) + Fe2Ti reaction. Transmission electron microscopy investigations showed that this solid-state transformation produced a fine intergrowth of the two ternary rare-earth compounds with a specific crystallographic orientation relation. The lower saturation magnetization of the splat/annealed condition as compared to the splat-quenched condition may reflect the disorderly intergrown Nd2(Fe,Ti)17 phase in NdFe11Ti. On the other hand the higher coercivity obtained for the splat-quenched condition seems related to the smaller scale of the microstructure due to a possible, albeit weak, pinning effect by the grain boundaries.