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arXiv · 1911.07139

Soft X-ray Absorption Spectroscopy and Magnetic Circular Dichroism as Operando Probes of Complex Oxide Electrolyte Gate Transistors

Biqiong Yu·Guichuan Yu·Jeff Walter·Vipul Chaturvedi·Joseph Gotchnik·John W. Freeland·Chris Leighton·Martin Greven
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Abstract

Electrolyte-based transistors utilizing ionic liquids/gels have been highly successful in the study of charge-density-controlled phenomena, particularly in oxides. Experimental probes beyond transport have played a significant role, despite challenges to their application in electric double-layer transistors. Here, we demonstrate application of synchrotron soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) as operando probes of the charge state and magnetism in ion-gel-gated ferromagnetic perovskite films. Electrochemical response via oxygen vacancies at positive gate bias in LaAlO$_3$(001)/La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$ is used as a test case. XAS/XMCD measurements of 4-25 unit-cell-thick films first probe the evolution of hole doping (from the O K-edge pre-peak) and ferromagnetism (at the Co L-edges), to establish a baseline. Operando soft XAS/XMCD of electrolyte-gated films is then demonstrated, using optimized spin-coated gels with thickness $\sim$1 $μ$m, and specific composition. Application of gate voltages up to +4 V is shown to dramatically suppress the O $K$-edge XAS pre-peak intensity and Co $L$-edge XMCD, thus enabling the Co valence and ferromagnetism to be tracked upon gate-induced reduction. Soft XAS and XMCD, with appropriate electrolyte design, are thus established as viable for the operando characterization of electrolyte-gated oxides.

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Biqiong Yu, Guichuan Yu, Jeff Walter, Vipul Chaturvedi, Joseph Gotchnik, John W. Freeland, Chris Leighton, Martin Greven. 2019-11-17. Soft X-ray Absorption Spectroscopy and Magnetic Circular Dichroism as Operando Probes of Complex Oxide Electrolyte Gate Transistors. https://doi.org/10.1063/1.5138645

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