High Pressure X-Ray Study of Anomalous Bulk Modulus of an Fe70Ni30 Invar Alloy

Pressure dependence of the lattice constant is measured for the pressure-stabilized fcc phase of an Fe 70 Ni 30 Invar alloy by high pressure X-ray diffraction method at 77.4 K. The bulk modulus B in the ferromagnetic phase is obtained to be (14 ±1) ×10 2 kbar. A discontinuous increase in B , Δ B , is found to be Δ B ≈700 kbar near 64 kbar. The magnitude Δ B at 77.4 K is the same as that observed at the ferromagnetic to paramagnetic phase transition at room temperature around 15 kbar.