Magnetic Anomalies Suggesting Premartensitic Transformation in Ordered and Disordered Fe–Pt Invar Alloys

Abstract

Magnetization measurements were carried out on ordered and disordered Fe–Pt Invar alloys under high magnetic fields up to 18 T. Several anomalies were observed in the temperature variations of magnetization and high-field susceptibility χ_HF in the concentration range where the structure is believed to be completely γ phase. In the ordered alloys, an anomalous reduction in χ_HF appears below the inflection temperature T_i as estimated to be 80±5 K for 26.0 at% Pt–Fe. The magnetization changes anomalously also at the same temperature. In the disordered alloys, the reduced magnetization M_s⁄M₀ decreases more gradually against reduced temperature T⁄T_c with increasing Fe content, while in the ordered alloys it decreases more quickly with increasing Fe content in the same manner as in Fe–Ni Invar alloys. These anomalies might be ascribed to the premartensitic transformation.