Control of oxygen vacancy ordering and multiferroicity in SrFeO2.5 thin films

Multiferroics are materials that exhibit more than one of the primary ferroic properties, such as ferroelectrics, ferromagnetism, and ferroelasticity [1]. Multiferroics have potential for applications as actuators, multi-states memory, and magneto-electric coupling devices. However, to realize wide applications of multiferroics, the room temperature multi-functionality is needed [2]. Here, we propose to perform XAS/XMCD measurements for room temperature multiferroic SrFeO2.5 thin films, which further shows oxygen vacancy channel (OVC) controlled property changes via ionic liquid gating (ILG). The bulk perovskite phase SrFeO3 (P-SFO) is a ferromagnetic metal, while the bulk brownmillerite phase SrFeO2.5 (BM-SFO) is an antiferromagnetic insulator that has atomically ordered OVC within the oxygen deficient tetrahedrally coordinated cobalt (FeO4) layers. However, it is reported that epitaxial BM-SFO thin films can show canted ferromagnetism by controlling OVC ordering, which was measured by commercial SQUID magnetometer (MPMS) (Fig. 1a-1e) [3]. BM-SFO also reveals room temperature ferroelectricity (Fig. 1f-1h). Moreover, the magneto-electric coupling can be shown in the tetrahedral chain network. These samples revealed vertically ordered OVCs. However, the OVC can be controlled by ILG which can further leads to the tuning of their physical properties such as ferroelectricity and ferromagnetism.