Surface properties of ferrimagnet europium iron garnet and its influence on magnetic proximity-induced anomalous Hall effect in heterostructures with a topological insulator (Bi,Sb)₂Te₃

Ko-Hsuan Chen^1*, Pei-Tze Chen¹, Wei-Nien Chen¹, Keng-Yung Lin², Hsuan-Ning Chen¹, Shang-Fan Lee³, Sheng-Qiang Zhou⁴, Chia-Hung Hsu⁵, Minghwei Hong², Jueinai Kwo¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
³Institute of Physics, Academia Sinica, Taipei, Taiwan
⁴Helmholtz-Zentrum Dresden-Rossendorf, HZDR-FWIM, Dresden, Germany
⁵National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Ko-Hsuan Chen, email:khchen@phys.nthu.edu.tw

Rare earth iron garnets (ReIGs), known for their good chemical, thermal, and magnetic stabilities along with low Gilbert damping, are promising in applications such as spintronic devices and magneto-optical sensors. Heterostructures comprising ReIG and topological insulators (TIs) or heavy metals have drawn considerable interest due to novel interfacial phenomena, including the topological Hall effect and spin-orbit torque switching. In this study, we investigate the surface properties of sputter-deposited europium iron garnet (EuIG) thin films and their influence on the magnetic proximity-induced anomalous Hall effect (AHE) in heterostructures with MBE-grown (Bi,Sb)₂Te₃ (BST). According to x-ray reflectivity analysis, stratified EuIG layers were discovered in the growth of films exposed to air and in those air-exposed films subjected to post high-temperature annealing in vacuum, likely caused by air contamination and Eu depletion during annealing. After adopting the approach of preparing all layers in vacuum, the stratified EuIG layer no longer forms. In comparing the room temperature AHE in BST samples grown on these two EuIG surfaces, the air-exposed one followed by high-temperature annealed and the pristine one, a notable increase in coercivity was observed in the former. The AHE coercivity result was consistent with magnetic hysteresis measurements from an alternating gradient magnetometer. These findings also support the modification of the top EuIG layer since the AHE is an interfacial phenomenon induced by the magnetic proximity effect. This work highlights the importance of EuIG surface properties and interface control in BST/EuIG heterostructures and may be applicable to other rare earth iron garnets, providing valuable insights for future spintronics applications.

Ko-Hsuan Chen and Pei-Tze Chen contributed equally to this work. We acknowledge the important contributions of Sheng-Xin Wang, Zih-Ping Huang, and Jui-Min Chia. This work is supported by the National Science and Technology Council (NSTC), Taiwan, under grant No. NSTC 112-2112-M-007-051.

Keywords: Rare-earth iron garnet, Magnetic topological insulator heterostructure, Heteroepitaxial interface, X-ray reflectivity, Anomalous Hall effect