From FeNi-Invar to FeNiMn reentrant spin-glasses

Abstract

Thirty years of Mössbauer spectroscopy correspond roughly to twenty-five years of FeNi-invar research using this method. The first systematic study of hyperfine fields in FeNi alloys, in both bcc and fcc phases, appeared in 1963, the first spectra were published probably in 1964. A very important fact is that fcc iron is an antiferromagnet; however, this iron phase is unstable at low temperature. In 1963, the possibility of performing low-temperature Mössbauer spectroscopy experiments on fcc iron precipitates in copper was shown. We shall demonstrate that the low temperature⁵⁷Fe Mössbauer spectra reveal a spatially inhomogeneous magnetic structure in FeNi-invar alloys. This structure corresponds to magnetic invar anomalies. From the viewpoint of basic research in magnetism, it was opportune to enhance these anomalies. One possible way to do this was the alloying of manganese into the invar matrix. In this contribution, we limited our examples to the study of the classical Fe_0.65Ni_0.35 and the new (Fe_0.65Ni_0.35)_1−x .Mn _x alloys, and refer to the literature with respect to other transition metal systems with similar properties. We will show the goal of Mössbauer spectrometry investigating the spin structure in disordered alloy systems via the vector nature of the hyperfine fields. Additionally, the combination of Mössbauer spectrometry with global techniques, i.e. DC magnetization and AC susceptibility allowed us to study the changes in magnetic properties of our disordered 3d transition metal alloys from a nearly collinear ferromagnet (pure FeNi-invar) over the reentrant spin-glasses and “pure” concentrated spinglasses towards the antiferromagnetic behaviour by varying the manganese concentration in small steps.