We have investigated the pressure variation of the volume and structure of an FCC Fe64Mn36 anti-ferromagnetic Invar alloy. The inclination of the pressurevolume (PV) curve of the FCC structure becomes discontinuous at a pressure of 4 GPa. According to the bulk modulus at zero pressure estimated by the BirchMurnaghan equation of state, the pressure between 4 and 10 GPa is 33 GPa larger than that at a pressure below 4 GPa. Considering previous experiments on magnetism at high pressure the Neel temperature at 4 GPa almost decreases to room temperature. These results suggest that the increase in the bulk modulus by 33 GPa can be attributed to the pressure-induced magnetic phase transition from anti-ferromagnetism to paramagnetism. Volume at zero pressure was estimated using the BirchMurnaghan equation of state. The volume of FCC structure in the anti-ferromagnetic state was 1.17% larger than the volume in the paramagnetic state, namely, the spontaneous magnetostriction was 1.17%. Pressure-induced structural transition from FCC to HCP occurs with an increase in the pressure, especially at up to 5 GPa. The value of c/a is 1.62; this value almost corresponds to that of an ideal HCP structure. The bulk modulus of the HCP structure estimated by the BirchMurnaghan equation of state is larger than that of the FCC structure, and the volume/atom ratio is smaller than that of the FCC structure.
- High pressure X-ray diffraction
- Invar effect
- Itinerant magnetism
- Magneto-volume effect
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics