Optical spectroscopy of magnons, electromagnons, phonons, and crystal field excitations in orthoferrites $R$FeO$_{\mathrm{3}}$

ORAL

Abstract

Mueller matrix ellipsometry and transmission polarimetry were used at Brookhaven National Lab to study multiferroic orthoferrites $R$FeO$_{\mathrm{3}}$ ($R=$Tb and Dy) in the far-IR range (10 - 2000 cm$^{\mathrm{-1}})$ and low temperatures and magnetic fields up to 10 T. Magnetic properties of $R$FeO$_{\mathrm{3\thinspace }}$are due to interplay of two magnetic subsystems: $R^{\mathrm{3+}}$ and Fe$^{\mathrm{3+}}$. Spectra of magnons, electromagnons, and optical phonons have been investigated and described in terms of the temperature and field dependencies of their frequency, damping, and oscillator strength. Below the magnetic ordering of $R^{\mathrm{3+}}$ spins $T_{\mathrm{N}}(R^{\mathrm{3+}})$, we observed hardening of the magnon frequencies and modification of the magnon selection rules. In TbFeO$_{\mathrm{3}}$ the quasi-AFM magnon gains electric-dipole activity below $T_{\mathrm{N}}$(Tb) and behaves as a hybrid mode. In addition to quasi-AFM and quasi-FM magnons in $R$FeO$_{\mathrm{3}}$, we discovered electromagnons which are electric-dipole active along the $c$-axis. The oscillator strength of electromagnon in DyFeO$_{\mathrm{3}}$ at 20 cm$^{\mathrm{-1\thinspace }}$provides a significant contribution of about 50{\%} to the static magnetodielectric effect. In contrast, the electromagnon in TbFeO$_{\mathrm{3}}$ at 27~cm$^{\mathrm{-1}}$ has a weaker strength and it appears only in a narrow temperature range 2.7 $-$ 3.3 K at $H=$0 and in a narrow range of magnetic fields \quad of \quad 2.4~ -~2.7~T applied along the $b$-axis at $T=$1.5~K. Spectra of the ir-active optical phonons and crystal field excitations were measured for all three orthorhombic axes of $R$FeO$_{\mathrm{3}}$.

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Authors

  • Andrei Sirenko

    NJIT, New Jersey Institute of Technology, New Jersey Inst of Tech

  • V. A. Martinez

    NJIT

  • Andrei Sirenko

    NJIT, New Jersey Institute of Technology, New Jersey Inst of Tech

  • Y. Janssen

    BNL

  • G. L. Carr

    BNL, Brookhaven National Laboratory, Brookhaven National Lab

  • Debbie Andres

    Department of Applied Physics and Department of Physics, Columbia University, Istituto Italiano di Tecnologia, Graphene Labs, Italy, Department of Physics and Astronomy, Purdue University, Department of Electrical Engineering, Princeton University, Department of Applied Physics and Applied Mathematics, Columbia University, NJIT, New Jersey Inst of Technology, New Jersey Inst of Tech, New Jersey Institute of Technology, Center for Advanced Radiation Sources, University of Chicago, High Pressure Science and Technology Advanced Research, State University of New York at Stony Brook, Rutgers University, NIST, Brookhaven National Laboratory, University of Chicago, University of South Florida, ETH Zurich, Max Planck POSTECH/Korea Research Initiative, University of Virginia, Rutgers University - Camden, New Jersey Institute of technology, Shaanxi Normal University, Pohang Science and Technology University, Sungkyunkwan University, Northern Illinois University and Argonne National Laboratory, Beijing National Laboratory for Condensed Matter Physics , and Institute of Physics, Chinese Academy of Sciences, Rutgers U., Orsova Engineers, U.S. Naval Research Laboratory, Center for Space Science and Engineering Research, Virginia Tech, Virginia., Princeton University, NASA Goddard Space Flight Center, Villanova University, SOFIA/USRA, Jet Propulsion Laboratory, Hudson Regional Health Commision, Rutgers University, College of William & Mary, Department of Physics, Drexel University, Drexel University, Drexel Universty, University of Massachusetts Amherst, Pohang Institue of Science and Technology, Indiana University - Purdue University Indianapolis, Department of Physics, University of Maryland, Naval Research Laboratory, Towson Univ, Rice University, Independence Blue Cross Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, Department of Physics, Temple University, PulseTorr LLC, Department of Chemistry, West Chester University, Department of Physics, West Chester University, College of William and Mary Dept. of Physics, University of Virginia Dept. of Materials Science and Engineering, United States Naval Academy, Rutgers The State University of New Jersey, Univ of Maryland-College Park, Los Alamos National Laboratory, POSTECH, New Jersey Institute of Technology, Department of Electrical and Computer Engineering, HamSCI/ARRL, Virginia Tech, Rutgers University-Camden, University of Washington, Rutgers, The State University of New Jersey

  • S-W. Cheong

    Rutgers U.