Atomic-Scale Magnetism of Cr-Doped Bi2Se3 Thin Film Topological Insulators.
Magnetic doping is the most common method for breaking time-reversal-symmetry surface states of topological insulators (TIs) to realize novel physical phenomena and to create beneficial technological applications. Here we present a study of the magnetic coupling of a prototype magnetic TI, that is, Cr-doped Bi2Se3, in its ultrathin limit which is expected to give rise to quantum anomalous Hall (QAH) effect. The high quality Bi2-xCrxSe3 epitaxial thin film was prepared using molecular beam epitaxy (MBE), characterized with scanning transimission electron microscopy (STEM), electrical magnetotransport, and X-ray magnetic circularly dichroism (XMCD) techniques, and the results were simulated using density functional theory (DFT) with spin-orbit coupling (SOC). We observed a sizable spin moment mspin = (2.05 ± 0.20) μB/Cr and a small and negative orbital moment morb = (-0.05 ± 0.02) μB/Cr of the Bi1.94Cr0.06Se3 thin film at 2.5 K. A remarkable fraction of the (CrBi-CrI)(3+) antiferromagnetic dimer in the Bi2-xCrxSe3 for 0.02 < x < 0.40 was obtained using first-principles simulations, which was neglected in previous studies. The spontaneous coexistence of ferro- and antiferromagnetic Cr defects in Bi2-xCrxSe3 explains our experimental observations and those based on conventional magnetometry which universally report magnetic moments significantly lower than 3 μB/Cr predicted by Hund's rule.
York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University , Nanjing 210093, China.|Spintronics and Nanodevice Laboratory, Department of Electronics, University of York , York YO10 5DD, United Kingdom.
Wenqing
W
Liu
Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
Damien
D
West
York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University , Nanjing 210093, China.|Department of Electrical Engineering, University of California, Los Angeles , Los Angeles, California 90095, United States.
Liang
L
He
York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University , Nanjing 210093, China.|Spintronics and Nanodevice Laboratory, Department of Electronics, University of York , York YO10 5DD, United Kingdom.
Yongbing
Y
Xu
Center of Electron Microscopy, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University , Hangzhou 310027, China.
Jun
J
Liu
York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University , Nanjing 210093, China.
Kejie
K
Wang
Center of Electron Microscopy, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University , Hangzhou 310027, China.
Yong
Y
Wang
Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE, United Kingdom.
Gerrit
G
van der Laan
York-Nanjing Joint Center (YNJC) for Spintronics and Nanoengineering, School of Electronics Science and Engineering, Nanjing University , Nanjing 210093, China.
Rong
R
Zhang
Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
Shengbai
S
Zhang
Department of Electrical Engineering, University of California, Los Angeles , Los Angeles, California 90095, United States.
Kang L
KL
Wang
XMCD; density functional theory; magnetic topological insulator; spin and orbital moments; spintronics