We grew and characterized Bi1-xSbx thin films on GaAs(111)A substrates by molecular beam epitaxy. By optimizing the growth condition, we were able to grow Bi1-xSbx thin films epitaxially with the Sb concentration ranging from 0% to 100% and the epitaxial orientation of Bi1-xSbx(001)//GaAs(111). The conductivity of Bi1-xSbx exceeds 105 Ω−1 m−1 and approaches those of bulk values for thick enough thin films, which are higher than those of other Bi-based topological insulators by at least an order of magnitude. From the temperature dependence of their electrical conductivity, we confirmed the existence of metallic surface states of Bi1-xSbx inside and outside of the topological insulating region. Our results demonstrate the potential of Bi1-xSbx as a spin Hall material with high conductivity and possibly large spin Hall angle for spintronic applications.
A magnetometer utilizing a cooled normal pickup coil and a high-T
c superconducting quantum interference device (SQUID) picovoltmeter was applied to nondestructive evaluation in an unshielded environment. The pickup coil of copper wire was cooled to T=77 K in order to decrease thermal noise from resistance. The magnetic field noise of the magnetometer was 130 pT/Hz1/2 and 10 pT/Hz1/2 at 100 Hz and 1 kHz, respectively, for the pickup coil with a 4.4 mm diameter. It was shown that the magnetometer could be moved in an unshielded environment without degradation of its performance. By moving the cooled pickup coil, we successfully detected a small crack on the backsurface of the Cu plate in an unshielded environment.
We report on the crystal growth as well as the structural and magnetic properties of Bi0.8Sb0.2 topological insulator (TI)/MnxGa1-x bi-layers grown on GaAs(111)A substrates by molecular beam epitaxy. By optimizing the growth conditions and Mn composition, we were able to grow MnxGa1-x thin films on Bi0.8Sb0.2 with the crystallographic orientation of Bi0.8Sb0.2(001)[1 1¯ 0]//MnGa (001)[100]. Using magnetic circular dichroism (MCD) spectroscopy, we detected both the L10 phase (x<0.6) and the D022 phase (x>0.6) of MnxGa1-x. For 0.50≤x≤0.55, we obtained ferromagnetic L10-MnGa thin films with clear perpendicular magnetic anisotropy, which were confirmed by MCD hysteresis, anomalous Hall effect as well as superconducting quantum interference device measurements. Our results show that the BiSb/MnxGa1-x bi-layer system is promising for perpendicular magnetization switching using the giant spin Hall effect in TIs.
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