Structural and magnetic properties of TbCu₇-type SmCo _7-xNi_x magnets produced by mechanical milling

We have prepared nanograin magnetic powders of SmCo_7-xNi _x ( x = 0.2, 0.3, 0.4, 0.5, 0.6, 1.0, 1.5, 2.0) alloys by ball milling followed by annealing at 700 °C for 2 h. Samples with x =0-1.0 show a single TbCu₇-type phase (1 : 7) structure, and the lattice parameters a and c of this structure decrease as the Ni content increases. The Curie temperature (T_c) of the 1 : 7 phase also decreases with increasing x, from 897 °C at x = 0 to 771 °C at x = 1.5 in these samples, but it is still found that the of (T_c) these SmCo _7-xNi_x samples is much higher than that of the equivalent SmCo_7-xM_x compounds, where M represents substituting atoms such as Ti, Zr, Cu, and Hf. Good square hysteresis loops are observed in the fine-grained samples with single 1 : 7 phase structure, and high roomtemperature intrinsic coercivities (_iH_c)of larger than 1.1 T are obtained in the samples with x =-1.5. The temperature coefficient (β) of (_iH_c) the was about -0.2%/°C in the temperature range of 25 °C-400 °C.