Short-range magnetic collapse of Fe under high pressure at high temperatures observed using x-ray emission spectroscopy

Understanding the high-pressure electronic properties of Fe still poses both theoretical and experimental challenges. Here, we evidence the short-range magnetic collapse of Fe in the $\ensuremath{\gamma}$ phase by x-ray emission spectroscopy carried out in situ under high-pressure and high-temperature conditions, up to 20 GPa and 1400 K. We find an abrupt decrease in the Fe spin state in $\ensuremath{\gamma}\text{-Fe}$ at high pressure similar in amplitude to the known $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\epsilon}$ magnetic collapse transition. A careful analysis of the Fe spin state in the $\ensuremath{\epsilon}$ phase indicates a sluggish diminution right above the transition pressure, bearing out recent predictions of residual, likely noncollinear, magnetism in this phase. In the $\ensuremath{\gamma}$ phase, our results demonstrate that the dominant mechanism at high pressure is a high-spin to low-spin transition. Implications for the elastic properties of Fe at extreme conditions are analyzed.