Exchange-Enhanced Paramagnetism and Weak Ferromagnetism in the Ni3Al and Ni3Ga Phases; Giant Moment Inducement in Fe-Doped Ni3Ga

TLDR

The reciprocal magnetic susceptibility of Ni₃Al and Ni₃Ga alloys follows a Stoner‑type curve, indicating a strongly varying density of states near the Fermi level and a low effective Fermi energy. The authors aimed to explain the large field‑induced magnetization increase at low temperatures by adopting an itinerant‑electron description. They combined magnetic measurements with low‑temperature specific‑heat data to infer the band shape at the Fermi level. The results show that raising Ni content to 74.5 % in Ni₃Al and 76 % in Ni₃Ga drives a transition from exchange‑enhanced paramagnetism to weak ferromagnetism, a behavior confirmed by strong magnetization curvature and linear σ² versus H/σ plots across all temperatures and fields, while Fe doping induces giant moments, though the findings only qualitatively support the Stoner model.

Abstract

Measuring the magnetization of various alloys in the Ni3Al and Ni3Ga phases, we found that going to higher Ni concentrations within these phases, a transition from strongly exchange enhanced paramagnetism to weak ferromagnetism takes place at 74.5 and 76 at.% Ni, respectively. The shape of the reciprocal magnetic susceptibility vs temperature curves measured between 4.2° and 300°K is of the Stoner type and suggests for these alloys a density-of-states curve varying appreciably in the Fermi region leading to a low effective Fermi energy. This conclusion is confirmed by the strong curvature of the magnetization in high magnetic fields. These results and the fact that an increase of the magnetic field applied on ferro-magnetic samples effects a large increase of the magnetization even at the lowest temperatures (4.2°K) and in the highest fields (200 kOe) led us to a description in terms of the itinerant electron model. The use of this model seems justified by the fact that in agreement with calculations by Edwards and Wohlfarth, the magnetic data of both paramagnetic and ferromagnetic compositions fit nicely on straight lines in σ2 vs H/σ plots, this being so for all temperatures (down to 4.2°K) and all magnetic fields between 4 and 200 kOe. Combining the magnetic data and low-temperature specific-heat data, we obtained some information on the bandshape at the Fermi level. We cannot conclude, however, to more than a nice qualitative agreement with the Stoner model at this moment. As would be expected in highly polarizable metals and alloys, small amounts of Fe dissolved both in paramagnetic and in ferromagnetic alloys in the Ni3Al and Ni3Ga phases lead to giant moment inducement.