Magneto-optical Kerr effect in Cr-doped (Bi,Sb)$_{2}$Te$_{3}$ Thin Films

ORAL

Abstract

When a three-dimensional (3D) topological insulator (TI) is interfaced with magnetism, the breaking of time reversal symmetry results in new phenomena such as the recently observed quantum anomalous Hall effect [C.-Z. Zhang \textit{et al., Science} \textbf{340}, 167 (2013)]. Thus motivated, we use the polar-mode magneto-optical Kerr effect (MOKE) to probe the temperature- and field-dependent magnetization in molecular beam epitaxy grown Cr-doped thin films of the 3D TI (Bi,Sb)$_{2}$Te$_{3}$. Square MOKE hysteresis loops observed at low temperatures indicate robust ferromagnetism with a perpendicular magnetic anisotropy and Curie temperature that varies from $\sim$ 5 K to $\sim$ 150 K, depending on sample details. A key question is the nature of the ferromagnetism: is it a carrier-mediated mechanism, Van Vleck mechanism or due to extrinsic clusters? We address this issue by varying the magnetic ion concentration and carrier density via sample composition as well as by varying the chemical potential by back gating. Finally, we use spatially-resolved MOKE to image the magnetization in these samples.

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Authors

  • Yu Pan

    Dept. of Physics, Penn State University

  • Bing Yao

    Dept. of Physics, Penn State University

  • Anthony Richardella

    Pennsylvania State University, Dept. of Physics, Penn State University, Department of Physics, Penn State University

  • Abhinav Kandala

    Dept. of Physics, Penn State University, Pennsylvania State University

  • Robert Fraleigh

    Dept. of Physics, Penn State University

  • Joon Sue Lee

    Dept. of Physics, Penn State University, University Park, PA 16802, Dept. of Physics, Penn State University

  • Nitin Samarth

    Physics Department, Pennsylvania State University, Dept. of Physics, Penn State University, Pennsylvania State University, Department of Physics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

  • Andrew L. Yeats

    Institute for Molecular Engineering, University of Chicago, Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637

  • D.D. Awschalom

    University of Chicago and UC Santa Barbara, Institute for Molecular Engineering, University of Chicago, Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637, Institute for Molecular Engineering, University of Chicago, Chicago, IL 60652, Center for Spintronics and Quantum Computation, University of California, Santa Barbara, CA, 93106, University of Chicago - Institute for Molecular Engineering, Center for Spintronics and Quantum Computation, University of California, Santa Barbara, CA 93106, USA