Structure and magnetic properties of La-Co-M alloys with nominal composition of LaCo7-xMx (M = Zr, or Ti, x=0-0.6)

Alloys with nominal composition LaCo7-xMx (M=Zr, or Ti and x = 0-0.6) were synthesized and characterized in the temperature range of 10-1273 K in fiel ds up to 5 T. The experimental results show that the effects of Zr or Ti do ping on the structure, phases present and magnetic properties of the LaCo7- xMx alloys are different. In the case of Zr, for as-east alloys, besides th e 1-5 (CaCu5) and 1-13 (NaZn13) phases, a new phase with T-c = 1073 similar to 1173 K was detected. This new phase is probably in a hexagonal structur e and shows a uniaxial anisotropy. After annealing at 1273 K, the 1-5 phase increases and almost dominates the materials when x = 0.3 similar to 0.5. It shows a strong uniaxial anisotropy with H-A = 95 similar to 135 kOe at b oth 300 K and 10 K. The T-c's are similar to 838 K, which is almost the sam e as that of LaCo5. In the case of Ti, besides the 1-5 and 1-13 phases, ano ther new phase with Th2Zn17 structure was formed by Ti doping and almost do minates the materials when x = 0.3 similar to 0.6. This phase exhibits a un iaxial anisotropy with H-A similar to 25 kOe at both 300 K and 10 K. T-c de creases from 998 K to 901 K when the Ti content increases from x = 0.25 to x = 0.6.