Structural and Magnetic Properties of ${\hbox{TbCu}}_{7}$ -type ${\hbox{SmCo}}_{7-x}{\hbox{Ni}}_{x}$ Magnets Produced by Mechanical Milling

We have prepared nanograin magnetic powders of SmCo
_7-x
Ni
_x
(x =0, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0, 1.5, 2.0) alloys by ball milling followed by annealing at 700degC for 2 h. Samples with x=0 -1.0 show a single TbCu
₇
-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 897degC at x= 0 to 771degC at x =1.5 in these samples, but it is still found that the T
_c
of these SmCo
_7-x
Ni
_x
samples is much higher than that of the equivalent SmCo
_7-x
M
_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 room-temperature intrinsic coercivities (
_i
H
_c
) of larger than 1.1 T are obtained in the samples with x = 0-1.5. The temperature coefficient (beta) of the
_i
H
_c
was about -0.2%/degC in the temperature range of 25degC-400degC.