Carrier-mediated ferromagnetism in the magnetic topological insulator Cr-doped (Sb,Bi)2Te3

Abstract

Magnetically doped topological insulators, possessing an energy gap created at the Dirac point through time-reversal-symmetry breaking, are predicted to exhibit exotic phenomena including the quantized anomalous Hall effect and a dissipationless transport, which facilitate the development of low-power-consumption devices using electron spins. Although several candidates of magnetically doped topological insulators were demonstrated to show long-range magnetic order, the realization of the quantized anomalous Hall effect is so far restricted to the Cr-doped (Sb,Bi)2Te3 system at extremely low temperature; however, the microscopic origin of its ferromagnetism is poorly understood. Here we present an element-resolved study for Cr-doped (Sb,Bi)2Te3 using X-ray magnetic circular dichroism to unambiguously show that the long-range magnetic order is mediated by the p-hole carriers of the host lattice, and the interaction between the Sb(Te) p and Cr d states is crucial. Our results are important for material engineering in realizing the quantized anomalous Hall effect at higher temperatures.

Impurity states in the magnetic topological insulator V:(Bi,Sb)2Te3

“…At low temperatures, small variations of the 3d impurity band affecting the d-shell filling and the bandwidth at E F , e.g. localization of the 3d impurity band, may strongly favor the ferromagnetic superexchange, and influence the onset of ferromagnetism and QAHS recently reported in these systems 2,8,9,14 .…”

“…Clearly the 3d-states of the transition metal impurities play a very important role on the magnetism in MTI, e.g. by providing additional mechanisms of ferromagnetic coupling 14,[17][18][19][20][21] , although yet not experimentally determined.…”

Effect of reflection and refraction on NEXAFS spectra measured in TEY mode

“…It is known (Toll, 1956;Stern, 1963;Young, 1977;Plaskett & Schatz, 1963;Vinogradov et al, 1988;Sheik-Bahae, 2005;Lucarini et al, 2005;Nash et al, 1995;Smith, 1977;Lee & Sindoni, 1997;André et al, 2010) that generally an integral in the form (8) ambiguously defines the dependence between the research papers imaginary and real parts of a function, i.e. additional arbitrary constants (zero-frequency phase term, Blashke factors) along with their own dispersive integral are possible.…”

“…The undeniable advantage of these methods is their high sensitivity to the local electronic and atomic structure of the object. This makes it equally applicable to the study of structure from isolated atoms and simple molecules to complex biological molecules, clusters, nanostructures, surface and bulk solids (Erbahar et al, 2016;Aetukuri et al, 2013;Ye et al, 2015).…”

“…At the same time, the Kramers-Kronig transform needs a large range of integration and as a consequence extrapolations outside the experimental energy range need to be applied. Despite the careful mathematical analysis of the complexity of such an approach (Toll, 1956;Stern, 1963;Young, 1977;Plaskett & Schatz, 1963;Vinogradov et al, 1988;Sheik-Bahae, 2005;Lucarini et al, 2005;King, 2009), up to now there has been no experimental confirmation of the identity of the shape of the near-edge structure of measured absorption spectra and the absorption spectra calculated from reflection spectra. This work is a first experimental attempt to clarify this problem.…”