Origin of room-temperature multiferroism in hexagonal LuFeO$_3$

ORAL

Abstract

Combined theoretical and experimental studies are carried out, focusing on the exchange interactions and their couplings with the structural instabilities in hexagonal LuFeO$_3$ (hLFO). We apply an extended Kugel-Khomskii model based on maximally localized Wannier functions generated from band structure calculations. The model clearly shows that the single occupied $d_{z^2}$ orbital in hLFO greatly increases the exchange coupling compared to that of hexagonal LuMnO$_3$ in which $d_{z^2}$ is empty. The interlayer exchange interaction is the key to the spin reorientation (SR) and weak ferromagnetic moment observed below 130K. Our calculations show that SR is strongly coupled to the $K_1$ phonon mode and only weakly dependent on $K_3$ and $\Gamma_2^{-}$ phonons. It indicates that the atomic displacements along positive direction of $K_1$ mode is responsible for the spin reorientation. This scenario is confirmed by our X-ray diffraction and X-ray absorption experiments. In the end, we propose that $T_{\rm SR}$ can be adjusted to be room temperature by structural competition between $K_1$ and $\Gamma_2^-$ modes in hLFO or by interface engineering.

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Authors

  • Xifan Wu

    • Physics Department, Temple University, Philadelphia, PA 19122, USA
    • Temple Univ
    • Temple University
    • Physics Department, Temple University, PA 19122, USA
    • Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA

  • Hongwei Wang

    • Physics Department, Temple University, PA 19122, USA

  • Igor Solovyev

    • National Institute for Material Science, Tsukuba , Japan

  • Jian Shen

    • Department of Physics, Fudan University, Shanghai 200433, China

  • Wenbin Wang

    • Department of Physics, Fudan University, Shanghai 200433, China

  • Xiao Wang

    • Department of Physics, Bryn Mawr College, Bryn Mawr, PA 19010, USA

  • Xuemei Cheng

    • Department of Physics, Bryn Mawr College, Bryn Mawr, PA 19010, USA

  • Lixin He

    • niversity of Science and Technology of China, Hefei, Anhui, China

  • Xiaoshan Xu

    • Department of Physics, University of Nebraska-Lincoln, NE , USA