Structure and magnetic properties of the ThMn12 type NdFeM alloys (M=Si/Al/B/transition metals)

Thirteen Nd(Fe,M)₁₂ alloys were studied, where M=Si, Al, B, Ti, V, Cr, Mn, Zr, Hf, Nb, W, Mo, or Ta. Those containing Si, Ti, V, Cr, Mn, Mo, or W are tetragonal ThMn₁₂ (1-12 for short) type structures. For the other alloys, the existence of Fe₃M, Fe₂M, FeM, and/or FeM₂ phases has been evidenced by X-ray diffraction (XRD). The size of the M atom is found to be crucial in determining its ability to stabilize the 1-12 phase. In NdFe _12-xTi_x alloys, the 1-12 phase exists in a wide range of x values from 0.7-2.0; however, the Fe₂Ti phase appears when x exceeds 1.0. Hence, NdFe₁₁Ti is probably not a line compound. For the other alloys with 1-12 phase, only x=2 was examined. The c/a value remains invariant at 0.558 to 0.559 when M is a transition metal, and equals 0.564 for M=Si. The Curie temperatures of these alloys, in decreasing order, are 310°C, 301°C, 278°C, 270°C, 252°C, 195°C, and 119°C for V, Si, Ti, Cr, W, Mo, and Mn, respectively. For the alloy with Ti, x=1, whereas for the others x=2. The anisotropy field for these alloys, measured for aligned polycrystalline powder at room temperature, is low; the maximum value is 26.8 kOe for NdFe₁₁Ti, which increases to 54.5 kOe at 4.2 K