Proximity Effect induced transport Properties between MBE grown (Bi1-xSbx)2Se3 Topological Insulators and Magnetic Insulator CoFe2O4

Abstract

In this study, we investigate the proximity effect in topological insulator (TI) and magnetic insulator bilayer system. (Bi_1-xSb_x)₂Se₃/CoFe₂O₄ (CFO) heterostructure was fabricated using molecular beam epitaxy and pulsed laser deposition system respectively. As revealed from the magnetoresistance measurement, the weak anti-localization (WAL) is strongly suppressed by proximity effect in (Bi_1-xSb_x)₂Se₃/CFO interface. Modified Hikama-Larkin-Nagaoka equation was used to fit the WAL results so that the size of surface state gap can be extracted successfully. The temperature-dependent resistance of the heterostructures at small and large perpendicular magnetic fields were also measured and analyzed. The results indicate that the surface band gap can be induced in TI and continuously enlarged up to 9 T, indicating the gradual alignment of the magnetic moment in CFO under perpendicular magnetic field. The approaches and results accommodated in this work show that CFO can effectively magnetize (Bi_1-xSb_x)₂Se₃ and the heterostructures are promising for TI-based spintronic device applications.

Figure 1

(a) X-ray diffraction patterns of single layer Bi₂Se₃, CoFe₂O₄ and bilayer (Bi_1-xSb_x)₂Se₃/CFO samples. (b) The RHEED patterns of Bi₂Se₃ which grew on CFO layer. (c) The schematic diagram of bilayer structure, and the inset is Hall bar pattern which observed by optic microscope.

Figure 2

Magnetoresistance measurements and fitting results of the magnetoconductivity in perpendicular magnetic fields. (a) Normalized MC of the single layer (Bi₂Se₃) sample (squares) and bilayer (Bi₂Se₃:Sb/CFO) samples (circles) at 2 K in the low field region. (b) The fitted Δ/2E _F with different Sb doping. (c) The fitted phase coherence length with different Sb doping. (d) and (e) display the fitted α ₁ (upper panel) and α ₀ (lower panel) as a function Sb ratio.

Figure 3

Temperature-dependent σ _xx of (a) Bi₂Se₃/CFO and (b) Bi₂Se₃Sb(0.6)/CFO samples are evaluated at B = 0, 0.1, 0.3, 0.5, 1, 5, and 9 T. The slopes are defined as $\mathrm{\kappa }=(\pi h/e^2)\mathrm{\Delta }{\sigma }_{xx}(B,T)/d(lnT)$, which is plotted as a function of B in (c) Bi₂Se₃/CFO and (d) Bi₂Se₃Sb(0.6)/CFO sample.

Figure 4

Schematic diagram of the bilayer structures in perpendicular external magnetic fields. The diagram shows that the gap size of surface state can increase with increasing the external B fields.