Anomalous low temperature spin reorientation in carbon substituted Pr–Co–B–C alloys

Abstract

We studied the effects of C substitution for B on structural and magnetic properties of Pr16Co76B8−xCx (0⩽x⩽8) alloys, prepared by mechanical alloying and subsequent annealing. An attempt to synthesize Pr2Co14C compound has been carried out by a gradual C substitution of B in Pr16Co76B8. The x-ray diffraction results show that after annealed at 1073K for 30min, Pr2Co14(B,C) phase with tetragonal Nd2Fe14B-type structure is formed as the main phase for 0⩽x⩽7. The Pr2Co14C phase has not been observed in mechanical alloyed B-free powders (x=8). The lattice parameter c of the Pr2Co14(B,C) phase decreases with increasing the carbon content. The highest coercivity of 21.9kOe has been obtained in Pr16Co76B6C2 alloys. The spin-reorientation temperature TSR1 increases with increasing the carbon content from 663K for x=0 to 685K for x=7. However, the spin reorientation is observed at 40K for Pr16Co76B6C2 and then the spin-reorientation temperature TSR2 is nearly unchanged at 125K for Pr16Co76B8−xCx alloys with x=4, 6, and 7, which may be caused by the solubility of carbon atoms. The anomaly of the spin reorientation observed at low temperatures in C-substituted Pr16Co76B8−xCx (x=2, 4, 6, and 7) alloys may be related to the Pr3+ instability.