Dynamics of the magnetic and structural a -> e phase transition in Iron

TL;DR

This study investigates the simultaneous magnetic and structural phase transition in iron under high pressure, revealing sharp, first-order transitions with a narrower pressure range than previously reported, and suggests magnetism drives the transition.

Contribution

It provides direct experimental evidence that magnetic changes precede structural transitions in iron under pressure, supporting theoretical predictions about magnetism's role in phase stability.

Findings

Magnetic and structural transitions are sharp and first order.

The transition occurs over a narrower pressure range (2.4 GPa) than previously reported.

Magnetic transition slightly precedes the structural transition.

Abstract

We have studied the high-pressure iron bcc to hcp phase transition by simultaneous X-ray Magnetic Circular Dichroism (XMCD) and X-ray Absorption Spectroscopy (XAS) with an X-ray dispersive spectrometer. The combination of the two techniques allows us to obtain simultaneously information on both the structure and the magnetic state of Iron under pressure. The magnetic and structural transitions simultaneously observed are sharp. Both are of first order in agreement with theoretical prediction. The pressure domain of the transition observed (2.4 $\pm$ 0.2 GPa) is narrower than that usually cited in the literature (8 GPa). Our data indicate that the magnetic transition slightly precedes the structural one, suggesting that the origin of the instability of the bcc phase in iron with increasing pressure is to be attributed to the effect of pressure on magnetism as predicted by spin-polarized full potential total energy calculations.