Structure and magnetic properties of La-Co-M alloys with nominal composition of LaCo/sub 7-x/M/sub x/ (M=Zr, or Ti, x=0-0.6)

Alloys with nominal composition LaCo/sub 7-x/M/sub x/ (M=Zr, or Ti and x=0-0.6) were synthesized and characterized in the temperature range of 10-1273 K in fields up to 5 T. The experimental results show that the effects of Zr or Ti doping on the structure, phases present and magnetic properties of the LaCo/sub 7-x/M/sub x/ alloys are different. In the case of Zr, for as-cast alloys, besides the 1-5 (CaCu/sub 5/) and 1-13 (NaZn/sub 13/) phases, a new phase with T/sub c/=1073/spl sim/1173 K was detected. This new phase is probably in a hexagonal structure and shows a uniaxial anisotropy. After annealing at 1273 K, the 1-5 phase increases and almost dominates the materials when x=0.3/spl sim/0.5. It shows a strong uniaxial anisotropy with H/sub A/=95/spl sim/135 kOe at both 300 K and 10 K. The T/sub c/'s are /spl sim/838 K, which is almost the same as that of LaCo/sub 5/. In the case of Ti, besides the 1-5 and 1-13 phases, another new phase with Th/sub 2/Zn/sub 17/ structure was formed by Ti doping and almost dominates the materials when x=0.3/spl sim/0.6. This phase exhibits a uniaxial anisotropy with H/sub A//spl sim/25 kOe at both 300 K and 10 K. T/sub c/ decreases from 998 K to 901 K when the Ti content increases from x=0.25 to x=0.6.