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Abstract Spin injection using ferromagnetic semiconductors at room temperature is a building block for the realization of spin-functional semiconductor devices. Nevertheless, this has been very challenging due to the lack of reliable room-temperature ferromagnetism in well-known group IV and III-V based semiconductors. Here, we demonstrate room-temperature spin injection by using spin pumping in a BiSb/(Ga,Fe)Sb heterostructure, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature (T C) and BiSb is a topological insulator (TI). Despite the very small magnetization of (Ga,Fe)Sb at room temperature (45 emu/cc), we detected spin injection from (Ga,Fe)Sb by utilizing the large inverse spin Hall effect (ISHE) in BiSb. Our study provides the first demonstration of spin injection at room temperature from a FMS.

Abstract Layered materials, such as graphene and transition metal dichalcogenides, are able to obtain new properties and functions through the modification of their crystal arrangements. In particular, ferromagnetism in polycrystalline MoS2 is of great interest because the corresponding nonmagnetic single crystals exhibit spontaneous spin splitting only through the formation of grain boundaries. However, no one has reported direct evidence of this unique phenomenon thus far. Herein, we demonstrate ferromagnetism modulation by an ultralow current density

Abstract Topological materials, such as topological insulators (TIs), have great potential for ultralow power spintronic devices, thanks to their giant spin Hall effect. However, the giant spin Hall angle (θ SH > 1) is limited to a few chalcogenide TIs with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler alloy topological semi-metal (HHA-TSM), YPtBi, it is possible to achieve both a giant θ SH up to 4.1 and a high thermal budget up to 600 °C. We demonstrate magnetization switching of a CoPt thin film using the giant spin Hall effect of YPtBi by current densities lower than those of heavy metals by one order of magnitude. Since HHA-TSM includes a group of three-element topological materials with great flexibility, our work opens the door to the third-generation spin Hall materials with both high θ SH and high compatibility with the BEOL process that would be easily adopted by the industry.

Abstract Spin orbit torque (SOT) magnetization switching of ferromagnets with large perpendicular magnetic anisotropy has a great potential for the next generation non-volatile magnetoresistive random-access memory (MRAM). It requires a high performance pure spin current source with a large spin Hall angle and high electrical conductivity, which can be fabricated by a mass production technique. In this work, we demonstrate ultrahigh efficient and robust SOT magnetization switching in fully sputtered BiSb topological insulator and perpendicularly magnetized Co/Pt multilayers. Despite fabricated by the magnetron sputtering instead of the laboratory molecular beam epitaxy, the topological insulator layer, BiSb, shows a large spin Hall angle of θ SH = 10.7 and high electrical conductivity of σ = 1.5 × 105 Ω−1 m−1. Our results demonstrate the feasibility of BiSb topological insulator for implementation of ultralow power SOT-MRAM and other SOT-based spintronic devices.

Half-Heusler alloy topological semimetal YPtBi is a promising candidate for an efficient spin source material having both large spin Hall angle θSH and high thermal stability. However, high-quality YPtBi thin films with low bulk carrier density are usually grown at 600 °C, which exceeds the limitation of 400 °C for back end of line (BEOL) process. Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films grown at lower growth temperature down to 300 °C. Although both effective spin Hall angle and spin Hall conductivity degraded with lowering the growth temperature to 300 °C due to degradation of the interfacial spin transparency, they were recovered by reducing the sputtering Ar gas pressure. We achieved a giant θSH up to 7.8 and demonstrated efficient spin–orbit torque magnetization switching by ultralow current density of ∼105 A/cm2 in YPtBi grown at 300 °C with the Ar gas pressure of 1 Pa. Our results provide the recipe to achieve giant θSH in YPtBi grown at lower growth temperature suitable for BEOL process.

It remains challenging to integrate topological insulators (TI) with magnetic tunnel junctions (MTJ) for spintronics applications. Here, the authors achieve a large tunneling magnetoresistance ratio and a low switching current density in a TI-MTJ device at room temperature, very promising for TI-driven magnetic memory.

We observe the signature of zero-field ground-state skyrmions in BiSb topological insulator/MnGa bilayers by using the topological Hall effect (THE). We observe a large critical interfacial Dzyaloshinskii-Moriya-Interaction (DMI) energy (DCS = 5.0 pJ/m) at the BiSb/MnGa interface that can be tailored by controlling the annealing temperature of the MnGa template. The THE was observed at room temperature even under the absence of an external magnetic field, which gives strong evidence of the existence of thermodynamically stable skyrmions in the MnGa/BiSb bilayers. Our results give insight to the role of interfacial DMI tailored by suitable material choice and growth technique for the generation of stable skyrmions at room temperature.

A large spin-splitting is essential for spintronic devices. Here, the authors observe a spontaneous spin-splitting energy of between 31.7 and 50 millielectronvolts in n-type indium iron arsenide at temperatures up to several tens of Kelvin, challenging the conventional theory of ferromagnetic semiconductors.

In order to understand the mechanism of the ferromagnetism in the ferromagnetic semiconductor Ga 1 − x Mn x As [(Ga,Mn)As], we have investigated the magnetic behavior on a microscopic level through systematic temperature (T)- and magnetic field (H)-dependent soft x-ray magnetic circular dichroism (XMCD) experiments at the Mn L 2 , 3 absorption edges. The T and H dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations (4% and 10.8%) and different Curie temperature (T C ) values (65, 120, and 164 K). In particular, the SPM component develops well above T C , indicating that local FM regions are formed well above T C . The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions rather than uniform electronic states considered by mean-field theories. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, provided by the present study will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families. [ABSTRACT FROM AUTHOR]