Magnetic properties of RNi4Fe alloys (R=La, Ce, or Y)

Abstract

Magnetization of several RNi4Fe alloys (R=La, Ce, or Y) has been studied over the temperature region 4 to ∼300 K and in applied fields up to 21 kOe. Replacement of Ni by Fe in the RNi5 systems expands the lattice and produces a significant alteration in magnetic behavior. In contrast with the RNi5 systems which do not order magnetically, the RNi4Fe alloys develop ferromagnetic order at low temperatures with Curie temperatures ranging from 195 to 270 K. Saturation magnetizations (in μB per formula unit at 4 K) were 5.0, 3.3, and 4.0 for R=La, Ce, and Y, respectively. The low moment of CeNi4Fe together with its anomalously small unit cell volume strongly suggests that Ce in this alloy is quadripositive. The magnetic behavior of the RNi4Fe systems indicates that Fe induces moments on the neighboring Ni atoms, ∼0.9 μB/Ni atoms in the case of LaNi4Fe. Below the Curie temperature, magnetization-temperature plots obtained using low field (4 kOe) show broad maximum for the La system whose origin as yet is not completely clear. The maximum disappears at applied fields ∼20 kOe, and hence it may arise from increased magnetic hardness at low temperatures.