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 LaCo_7-xM_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_7-xM_x alloys are different. In the case of Zr, for as-cast alloys, besides the 1-5 (CaCu₅) and 1-13 (NaZn₁₃) phases, a new phase with T_c=1073~1173 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=0.3~0.5. It shows a strong uniaxial anisotropy with H_A=95~135 kOe at both 300 K and 10 K. The T_c´s are ~838 K, which is almost the same as that of LaCo₅. In the case of Ti, besides the 1-5 and 1-13 phases, another new phase with Th ₂Zn₁₇ structure was formed by Ti doping and almost dominates the materials when x=0.3~0.6. This phase exhibits a uniaxial anisotropy with H_A~25 kOe at both 300 K and 10 K. T_c decreases from 998 K to 901 K when the Ti content increases from x=0.25 to x=0.6