Mössbauer Study ofCo57(Fe57) in Cobaltous Oxide at High Pressure

We report a room-temperature study of the Mössbauer effect of divalent ${\mathrm{Co}}^{57}$ (${\mathrm{Fe}}^{57}$) in cobaltous oxide up to pressures of about 250 kbar. As pressure is applied, the velocity spectrum unfolds from a single line into a hyperfine pattern in a manner consistent with the measured increase of the Néel temperature with pressure as reported by D. Bloch. The pressure dependences of the internal magnetic field, electric field gradient, and isomer shift are described.