Recently, topological insulator(TI)/ferromagnetic(FM) systems, such as Bi2Se3/FM 1,2, Bi1-xSbx/FM 3,4 have attracted much attention with their promising properties for emerging memory technologies, such as magnetic random-access memories(MRAM). Indeed, these systems may drastically reduce the writing current using spin-orbit torque(SOT) switching. In this case SOT is generated by injecting a charge current into the TI topologically protected surface states(SS), then converted into a spin current in the FM layer. The charge current may shunt the TI SS through the metallic FMs which conductivity is often higher and may not contribute efficiently to the SOT5. Thus, FMs with lower conductivities are required and may help to better understand the SOT effect. Also, for applications, FMs with high Curie temperature and perpendicular magnetic anisotropy(PMA) are desirable.

In this work, we focused on the molecular beam epitaxy (MBE) growth conditions of Bi1-xSbx(top)/MnxGa1-x(bottom) heterostructure on the semi-insulating GaAs(001) substrate. A high epitaxial quality was confirmed by the high-resolution scanning transmission electron microscopy (STEM) as shown in Fig.1. The Bi0.85Sb0.15 top surface states have been characterized by performing ARPES measurements. Electronic band structure with topological surface states was observed. Mn0.45Ga0.55 exhibit a PMA with a magnetization of 315 kA/m.

To investigate the charge-to-spin current conversion of Bi0.9 Sb0.1(9 nm)/Mn0.45Ga0.55(7 nm) we first performed anomalous Hall effect (AHE) measurements at various temperatures. A large value of ΔRAHE = 0.4Ω was obtained at room temperature. We then perform second harmonic Hall voltage measurements in order to quantify the damping-like HDL(Fig.2.) and field-like SOT HFL by applying an ac current and in-plane external magnetic field. For this relatively large MnGa thickness (7nm), a value of HDL=2.6±1.3mT for a current density of 1010 A/m2 was estimated. Part of future work will focus on controlling the growth of a thinner layer.

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