Mössbauer studies on the superparamagnetic behavior of 69–31 at.% FeNi fine particles

The Mössbauer effect is used to study the superparamagnetic behavior of fine particles of 69–31 at.% FeNi alloy. The Mössbauer spectrum of the alloy consists of a central single line and a six-line magnetic hyperfine pattern for fine particles; but the single line disappears for larger particles, which is in disagreement with the previously reported interpretation that the central single line originates from the paramagnetic state of the antiferromagnetic regions in the ferromagnetic alloy. It is suggested that the central line originates from the superparamagnetic behavior of the ferromagnetic or antiferromagnetic fine particles.