Walter Jeff, Voigt Bryan, Day-Roberts Ezra, Heltemes Kei, Fernandes Rafael M, Birol Turan, Leighton Chris
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
Department of Physics, Augsburg University, Minneapolis, MN 55454, USA.
Sci Adv. 2020 Jul 29;6(31):eabb7721. doi: 10.1126/sciadv.abb7721. eCollection 2020 Jul.
Increasingly impressive demonstrations of voltage-controlled magnetism have been achieved recently, highlighting potential for low-power data processing and storage. Magnetoionic approaches appear particularly promising, electrolytes and ionic conductors being capable of on/off control of ferromagnetism and tuning of magnetic anisotropy. A clear limitation, however, is that these devices either electrically tune a known ferromagnet or electrically induce ferromagnetism from another magnetic state, e.g., antiferromagnetic. Here, we demonstrate that ferromagnetism can be voltage-induced even from a diamagnetic (zero-spin) state suggesting that useful magnetic phases could be electrically induced in "nonmagnetic" materials. We use ionic liquid-gated diamagnetic FeS as a model system, showing that as little as 1 V induces a reversible insulator-metal transition by electrostatic surface inversion. Anomalous Hall measurements then reveal electrically tunable surface ferromagnetism at up to 25 K. Density functional theory-based modeling explains this in terms of Stoner ferromagnetism induced via filling of a narrow band.
近来，电压控制磁性方面越来越令人印象深刻的演示得以实现，凸显了其在低功耗数据处理和存储方面的潜力。磁离子方法似乎特别有前景，电解质和离子导体能够对铁磁性进行开/关控制并调节磁各向异性。然而，一个明显的局限在于，这些器件要么通过电来调节已知的铁磁体，要么从另一种磁态（例如反铁磁体）电诱导出铁磁性。在此，我们证明即使从抗磁（零自旋）态也能电压诱导出铁磁性，这表明在“非磁性”材料中可以电诱导出有用的磁相。我们使用离子液体门控的抗磁体FeS作为模型系统，表明仅1 V就能通过静电表面反转诱导出可逆的绝缘体 - 金属转变。反常霍尔测量随后揭示了在高达25 K时电可调的表面铁磁性。基于密度泛函理论的建模从通过填充窄带诱导的斯托纳铁磁性角度对此进行了解释。
