Study on the solidification path and magnetic properties of the ternary Nd6Fe13M (M=Cu, Ga, Ge) compounds

Abstract

The intergranular Nd₆Fe₁₃M phase can effectively enhance the coercivity and thermal stability of NdFeB magnets. Investigating the magnetic properties and solidification path of Nd₆Fe₁₃M is crucial for understanding its mechanism in improving the coercivity of NdFeB magnets, as well as providing essential guidance for optimizing the preparation process of NdFeB-based alloys. In this work, a series of Nd₆Fe₁₃M (M = Cu, Ga, Ge) samples were prepared via arc melting, and their solidification path and magnetism were studied in detail. It is confirmed that the ternary Nd₆Fe₁₃M phase forms via the peritectic reaction Liquid + Fe₁₇Nd₂ ↔ Nd₆Fe₁₃M. The formation temperatures of Nd₆Fe₁₃Cu, Nd₆Fe₁₃Ga, and Nd₆Fe₁₃Ge were determined to be 875 K, 1064 K and 1206 K, respectively. Rietveld refinement confirmed that Nd₆Fe₁₃M adopts a tetragonal Nd₆Fe₁₃Si-type structure with the I4/mcm space group. Magnetic measurements revealed that all compounds exhibit antiferromagnetic ordering, with Néel temperatures of 400 K, 429 K, and 422 K, respectively. Notably, a magnetic field-induced transition from antiferromagnetic to ferromagnetic state was observed in Nd₆Fe₁₃Ge at 150 K under a maximum applied field of 5 T. Furthermore, analysis of the hysteresis loops of Nd₆F_e13Cu and Nd₆Fe₁₃Ga at different temperatures suggests a competitive interplay between antiferromagnetic and ferromagnetic coupling in RE₆Fe₁₃M, with increasing temperature weakening the antiferromagnetic coupling strength.