Magnetic depth profiling of Fe3O4/SrTiO3 heterostructures to reveal dynamics of interfacial switching

Controlling the oxide interfaces is the key towards controlling the switching phenomenon and thus realizing functional devices. We found that oxide substrates can take an active part in the redox process at the interface and may be even used to tune properties. Hence, our next goal is to real-time monitor the redox reactions at the interface when the properties or "iron oxide phases" of the interfaces and the films are tuned. We have characterized our samples using different lab techniques, e.g. XRR, XRD, SQUID and GISAXS, or using large scale X-ray facilities, e.g. HAXPES and XMCD. Using SQUID, we observe the disappearance of Verwey transition, the characteristic temperature for Fe3O4, when applying a positive voltage. This indicates a perturbation of oxygen content in the Fe3O4 phase and possible switching to the insulator gamma-Fe2O3 phase at the interface. Thus, our next step is to monitor in-situ the magnetic depth profiling when applied electric field using polarized neutron reflectivity in order to real-time monitor the thickness and the composition of the intralayer.

控制氧化物界面是调控开关现象并进而实现功能器件的关键。我们发现，氧化物衬底（oxide substrates）可积极参与界面处的氧化还原过程，甚至可用于调控性能。因此，我们的下一个目标是在调控界面和薄膜的性能或“氧化铁相（iron oxide phases）”时，对界面处的氧化还原反应进行实时监测。我们已利用多种实验室技术（如XRR、XRD、SQUID和GISAXS）或大型X射线设施（如HAXPES和XMCD）对样品进行了表征。通过SQUID观测发现，施加正电压时，Fe3O4的特征温度——Verwey转变（Verwey transition）消失。这表明Fe3O4相中的氧含量发生了扰动，且界面处可能转变为绝缘相γ-Fe2O3。因此，我们的下一步是利用极化中子反射（polarized neutron reflectivity）技术，在施加电场时原位监测磁深度剖面，以实时追踪层内厚度与成分变化。