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

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 / M 0 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.