α−ε transition pathway of iron under quasihydrostatic pressure conditions

We have carefully investigated the α-ε 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 α-ε structural transition, which is in contrast to the scenario that the transition is driven by the pressure-induced instability of the ferromagnetism in α phase of iron. We conclude that shear stress is important to initiate the α-ε transition. Our model to fit the EXAFS profile demonstrates that the local atomic arrangement in ε phase is slightly distorted due to unfinished shuffle motion, whereas shear motion finishes at the beginning of the transition.