Occurrence of Invar Anomalies in Binary Alloys of Fe with Ni, Pd, Pt, and Mn

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Abstract
The Invar anomalies in the Fe–Ni, –Pd, –Pt, and –Mn binary alloy systems are explained by a model based on concepts which have recently been successful in the interpretation of transition metal alloy properties. The various near‐neighbor atomic configurations about an Fe atom are assumed to have a considerable effect on the electronic structure at this Fe atom. The atomic distribution is not random; the alloys are assumed to be inhomogeneous, and to contain small regions of ordered compound (FeNi3, FePd, FePt) or Mn rich clusters. These assumptions are sufficient to allow a common explanation of the relative intensity and composition dependence of the Invar anomalies, in particular the magnetoelastic coupling, in all four systems. Many physical and metallurgical properties of these systems, the temperature and composition dependence of the magnetization, the alloy instability, and the large effect of cold work are related through this model. For the Fe–Ni system, the model prediction of exchange coupling between small, coexisting ferromagnetic and antiferromagnetic regions at low temperatures explains the composition independent drop in the magnetoelastic coupling below 20 K as well as the existence of a time‐dependent volume anomaly observed below 10 K.