Inhomogeneity and Invar effect in Fe-Pt alloys

Abstract

In order to clarify the causality between the Invar effect and the inhomogeneity, which has been considered as an essential origin of Invar effect, we studied ordered state, A, and disordered state, B, of Fe‐Pt Invar alloys, where A is thought as homogeneous and B as random. For Fe7 2Pt2 8 alloy, following results were obtained: At 4.2 K, magnetic moment is not sensitive to the atomic ordering (2.15 u B for A and 2.13 u B for B), while the hyperfine field at Fe nuclei is sensitive to the atomic ordering (342 kG for A and 363 kG for B) and distributes more widely in B, without superposition of two kinds of spectra. The Curie temperature, Tc, is 505 K for A and 371 K for B. At around Tc, negative thermal expansion coefficients with large magnitude have been obtained (−0.68×10− 5 K− 1 for A and −3.4×10− 5 K− 1 for B), and the magnetization changes against temperature more sharply for B. From these observations, we may safely conclude that the effect of inhomogeneities, i.e. atomic randomness, coexistence of two magnetic states and so forth, does not play an important role in the Invar effect.