<span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>α</mi><mo>−</mo><mi>ε</mi></math></span> transition pathway of iron under quasihydrostatic pressure conditions

Abstract

We have carefully investigated the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ transition pathway of iron under quasihydrostatic pressures. For this purpose, combined measurements of extended x-ray absorption fine structure (EXAFS) and x-ray magnetic circular dichroism at the Fe $K$ edge were performed using a helium pressure-transmitting medium. Collapse of the ferromagnetism simultaneously occurs with the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ structural transition, which is in contrast to the scenario that the transition is driven by the pressure-induced instability of the ferromagnetism in $\ensuremath{\alpha}$ phase of iron. We conclude that shear stress is important to initiate the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ transition. Our model to fit the EXAFS profile demonstrates that the local atomic arrangement in $\ensuremath{\epsilon}$ phase is slightly distorted due to unfinished shuffle motion, whereas shear motion finishes at the beginning of the transition.