Magnetism of ThCo5-based alloys

Abstract

Magnetic behavior of ThCo5, Th1−xYxCo5 and Th1−xYxCo4Fe has been determined over the temperature range 4 K to the Curie temperature in applied fields up to 120 kOe. Crystal parameters, saturation magnetization and anisotropy fields are presented for ThCo5, for Th1−xYxCo5 with x=0.1, 0.2, 0.4, 0.6 and 0.8 and for Th1−xYxCo4Fe with x=0.2, 0.4, 0.6 and 0.8. ThCo5 is observed to be exceptionally hard, not achieving saturation at 120 kOe. Co in this compound exhibits an anomalously low moment, ∼1.13 μB (as determined at 120 kOe). The Co moment rapidly increases as Y replaces Th in ThCo5, achieving for x=0.2 a value of 1.5 μB, the same as in YCo5. The anisotropy field (HA) for Th1−xYxCo5 ternaries at 4.2 K rises from 175 to 203 kOe as x increases from 0 to 0.2 and subsequently falls to 175 kOe for Th.2Y.8Co5. HA increases by 41 kOe between ThCo5 and ThCo4Fe. In contrast with the behavior of (Th, Y)Co5 ternaries progressive replacement of Th by Y in ThCo4Fe leads to a monatomic decline in HA. Changes of HA by alloying is ascribed to (a) preferential site occupancy or (b) band modification effects and often these cannot be separated. Present results indicate that these two effects are comparable in magnitude.