Structure and Magnetic Properties of the ThMn₁₂ Type NdFeM Alloys (M=Si/Al/B/Transition Metals)

Among the 13 Nd(Fe, M)₁₂ alloys studied, where M=Si, Al B, Ti, V, Cr, Mn, Zr, Ht, Nb, W, Mo, and Ta, those with Si, Ti, V, Cr, Mn, Mo, and W are tetragonal ThMn₁₂(1-12 for short) type structure. For the other alloys, existence of either Fe₃M, Fe₂M, FeM, and/or FeM2 phases is evidenced from X-ray diffraction (XRD). The size of M atom is found crucial in determining its ability to stabilize the 1–12 phase. When M is Ti in NdFe _12-xM_x alloys, the 1–12 phase exists in a wide range or x-values from 0.7-2.0, however Fe₂Ti phase appears when x exceeds 1.0. Hence NdFe₁₁Ti is not likely a line compound. For the other alloys with 1–12 phase only x=2 was examined. The c/a value keeps invariant at 0.558 to 0.559 when M is transition metal, and 0.564 for M = si. Curie temperatures(Tc) of these alloys, in decreasing order of M, are V (310 C), Si (301 C), Ti (278 C), Cr (270 C), W (252 C), Mo (195 C), and Mn (119 C); for the alloy with Ti, x=1 and for the others x=2. The determined anisotropy field (Ha) for these alloys from aligned polycrystalline powder at room temperature is low, the maximum one is 26.8 kOe for NdFe₁₁Ti, which increases to 54.5 kOe at 4.2 K.