Independent Tuning of Electronic Properties and Induced Ferromagnetism in Topological Insulators with Heterostructure Approach

Abstract

The quantum anomalous Hall effect (QAHE) has been recently demonstrated in Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures below 100 mK. In those materials, the spins of unfilled d-electrons in the transition metal dopants are exchange coupled to develop a long-range ferromagnetic order, which is essential for realizing QAHE. However, the addition of random dopants does not only introduce excess charge carriers that require readjusting the Bi/Sb ratio, but also unavoidably introduces paramagnetic spins that can adversely affect the chiral edge transport in QAHE. In this work, we show a heterostructure approach to independently tune the electronic and magnetic properties of the topological surface states in (BixSb1-x)2Te3 without resorting to random doping of transition metal elements. In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium iron garnet (YIG), a high Curie temperature (∼550 K) magnetic insulator, we find that the TI surface in contact with YIG becomes ferromagnetic via proximity coupling which is revealed by the anomalous Hall effect (AHE). The Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is varied, the AHE resistivity scales with the longitudinal resistivity. In this approach, we decouple the electronic properties from the induced ferromagnetism in TI. The independent optimization provides a pathway for realizing QAHE at higher temperatures, which is important for novel spintronic device applications.

Above 400-K robust perpendicular ferromagnetic phase in a topological insulator

“…Meanwhile, the resulting perpendicular anisotropy is sufficiently strong to drive the magnetization in the direction normal to the film plane without any external magnetic field. TIG/TI heterostructures are subsequently fabricated by growing a five–quintuple layer (QL)–thick (Bi x Sb 1− x ) 2 Te 3 TI film atop TIG using molecular beam epitaxy (MBE) ( 12 , 17 , 24 ). These TI films show excellent structural quality, as confirmed by in situ reflection high-energy electron diffraction (RHEED) patterns (see fig.…”

Surface-State-Dominated Spin-Charge Current Conversion in Topological-Insulator–Ferromagnetic-Insulator Heterostructures

“…To further verify that the spin-charge conversion efficiency is dominated by the sur- which can induce ferromagnetism at low temperature [30]. At room temperature, the Cr doping mainly changes the transport properties and the SOC strength of the bulk states.…”

Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators

“…Last but not least, other FM insulators with high T C , such as yttrium iron 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 55 garnet (YIG) (T C~5 50 K) [93] in addition to EuS (~16.5 K) [59] and EuO (Tc~77 K), can be applied as proximity layer. The high T C of FM insulators is very beneficial for realizing the QAH state at higher temperature.…”