Magnetic phase diagram of $Sr_3 Fe_2 O_{7-x}$

TL;DR

This study maps the magnetic phase diagram of Sr_3Fe_2O_{7-x} across different oxygen contents, revealing complex magnetic and electronic transitions, and contrasting properties with similar ruthenates and manganates.

Contribution

It provides detailed experimental insights into the magnetic and electronic phases of Sr_3Fe_2O_{7-x} as a function of oxygen content, highlighting unique incommensurate and commensurate antiferromagnetic orders.

Findings

Charge-disproportionation transition at 340 K in fully oxygenated sample

Incommensurate antiferromagnetic order below 115 K for x=0

High-temperature commensurate antiferromagnetic order below 600 K for x=1

Abstract

Magnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe^{4+}-containing perovskite-related phase Sr_3Fe_2O_7-x as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully-oxygenated compound (x=0) exhibits a charge-disproportionation transition at T_D = 340 K, and an antiferromagnetic transition at T_N = 115 K. For temperatures T \leq T_D, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe^{4+} moments. The fully-deoxygenated compound (x=1) is highly insulating, and its Fe^{3+} moments exhibit commensurate antiferromagnetic order below T_N ~ 600 K. Compounds with intermediate x exhibit different order with lower T_N, likely as a consequence of frustrated exchange interactions between Fe^{3+} and Fe^{4+} sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported.