Emerging Magnetism in Functional Heterostructures
Yuan-Chieh Tseng1*
1Materials Science & Engineering, National Chiao Tung University, Taiwan
* Presenter:Yuan-Chieh Tseng, email:yctseng21@mail.nctu.edu.tw
In this work I introduce you two examples of using operando x-ray spectroscopy to investigate emerging magnetism in functional heterostructures. In first case we investigated the effects of external voltage on the spin-electronic and transport properties at the interface of a Fe/ZnO device. Layer-, element-, and spin-resolved information of the device was obtained by cross-tuning of the x-ray mode and photon energy, when voltage was applied. At the early stage of the operation, the device exhibited a low-resistance state featuring robust Fe-O bonds. However, the Fe-O bonds were broken with increasing voltage. Breaking of the Fe-O bonds caused the formation of oxygen vacancies and resulted in a high-resistance state. Such interface reconstruction was coupled to a charge-transfer effect via Fe-O hybridization, which suppressed/enhanced the magnetization/coercivity of Fe electronically. Nevertheless, the interface became stabilized with the metallic phase if the device was continuously polarized. During this stage, the spin-polarization of Fe was enhanced whereas the coercivity was lowered by voltage, but changes of both characteristics were reversible. This stage is desirable for spintronic device applications, owing to a different voltage-induced electronic transition compared to the first stage.

In second case, reports on a novel magnetic device with a [Co40Pd60/Cu]10/Fe structure for use in the detection of H2. In a magneto-optical, transport and gas-detection system, the proposed device presented sharp, reversible H2-dependent magnetic/electrical properties. The electrical signal-to-noise ratio of the device can be restored ~ 50% by exposing it to a magnetic field, even when the sensitivity of the device dropped at low H2 pressure (0.7 KPa). This demonstrates the applicability of the device for use as a low-pressure H2 detector. Operando x-ray spectroscopy revealed that changes in H2-induced magnetism arose from a Co-Pd charge transfer effect coupled to changes in local-structure symmetry.

Keywords: synchrotron x-ray, spintronics