Magnetic phase diagram of iron at high pressure and temperature

Abstract

Crystallographic structure and long-range magnetic order of iron have been measured in pressure-temperature domains of 2--18 GPa and 300--800 K, using x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) in resistively heated diamond anvil cells under hydrostatic pressurizing conditions. A fine coverage of pressure-temperature space allowed monitoring $\ensuremath{\alpha}\ensuremath{\leftrightarrow}\ensuremath{\epsilon}, \ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\gamma}$, and $\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\epsilon}$ transformations, evidencing large metastability phenomena. $\ensuremath{\alpha}$-Fe remains ferromagnetic under high pressure and temperature in its whole stability domain, and no magnetic response could be measured with XMCD in pure $\ensuremath{\gamma}$-Fe and $\ensuremath{\epsilon}$-Fe. Structural and magnetic transformations are observed concomitantly within experimental uncertainties.