Abstract
The present high-pressure studies of to 30 GPa using x-ray diffraction, along with Mössbauer and Fe and -edge x-ray absorption spectroscopy methods, reveal a sequence of intricate structural/electronic-magnetic pressure-induced transitions. The low-pressure structure (0–18 GPa) is composed of sheets of ions alternating with layers of dumbbells, the latter oriented along the axis. This structure is characterized by an unusual positive . At 18 GPa a structural transition takes place to a more isotropic structure with the axis tilted from the axis and with negative . This transition corroborates with the onset of long-range antiferromagnetic order. Starting at , with an initial volume reduction in , the Cu-Fe bands overlap and this leads to a interionic valence exchange in about 1/3 of the at 27 GPa. As a result: (i) the becomes fourfold coordinated and is in a new crystallographic structure with space group , and (ii) the Néel temperature increases above twofold . This sequence of transitions is reversible with minimal hysteresis.
- Received 20 August 2009
DOI:https://doi.org/10.1103/PhysRevB.81.104110
©2010 American Physical Society