Electrical manipulation of spins is essential to design state-of-the-art spintronic devices and commonly relies on the spin current injected from a second heavy-metal material. The fact that chiral antiferromagnets produce spin current inspires us to explore the magnetization switching of chiral spins using self-generated spin torque. Here, we demonstrate the electric switching of noncollinear antiferromagnetic state in Mn3Sn by observing a crossover from conventional spin-orbit torque to the self-generated spin torque when increasing the MgO thickness in Ta/MgO/Mn3Sn polycrystalline films. The spin current injection from the Ta layer can be controlled and even blocked by varying the MgO thickness, but the switching sustains even at a large MgO thickness. Furthermore, the switching polarity reverses when the MgO thickness exceeds around 3 nm, which cannot be explained by the spin-orbit torque scenario due to spin current injection from the Ta layer. Evident current-induced switching is also observed in MgO/Mn3Sn and Ti/Mn3Sn bilayers, where external injection of spin Hall current to Mn3Sn is negligible. The inter-grain spin-transfer torque induced by spin-polarized current explains the experimental observations. Our findings provide an alternative pathway for electrical manipulation of non-collinear antiferromagnetic state without resorting to the conventional bilayer structure.

We demonstrate an ultrathin and semitransparent anisotropic and spin Hall magnetoresistance sensor based on NiFe/Pt heterostructure. The use of spin-orbit torque effective field for transverse biasing allows to reduce the total thickness of the sensors down to 3 -4 nm and thereby leading to the semitransparency. Despite the extremely simple design, the spin-orbit torque effective field biased NiFe/Pt sensor exhibits level of linearity and sensitivity comparable to those of sensors using more complex linearization schemes. In a proof-of-concept design using a full Wheatstone bridge comprising of four sensing elements, we obtained a sensitivity up to 202.9 mΩ Oe -1 , linearity error below 5%, and a detection limit down to 20 nT. The transmittance of the sensor is over 50% in the visible range.

We report on investigation of spin Hall magnetoresistance sensor based on NiFe/ AuxPt1-x bilayers. Compared to NiFe/Pt, the NiFe/AuxPt1-x sensor exhibits a much lower power consumption (reduced by about 57%), due to 80% enhancement of spin-orbit torque efficiency of AuxPt1-x at an optimum composition of x = 0.19 as compared to pure Pt. The enhanced spin-orbit torque efficiency allows to increase the thickness of NiFe from 1.8 nm to 2.5 nm without significantly increasing the power consumption.We show that, by increasing the NiFe thickness, we were able to improve the working field range (± 0.86 Oe), operation temperature range (150 o C) and detectivity (0.71 nT/√Hz at 1 Hz) of the sensor, which is important for practical applications.In the past few decades, a variety of magnetoresistance (MR) sensors have been developed and commercialized for diverse industrial and consumer applications, 1-6 including in the rapidly developing internet-of-things (IoT) paradigm and related technologies. 7 These include the anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) sensors. 1,8-10 All these sensors require sophisticated transverse biasing scheme for achieving linear response to an external field. 11 Recently we have demonstrated a spin Hall magnetoresistance (SMR) sensor using spin orbit torque (SOT) induced field-like effective field as the built-in linearization mechanism. 12,13 The use of SOT biasing greatly simplifies the sensor design, which consists of only a NiFe/Pt bilayer. 11 Furthermore, since the SMR is a second order effect, it allows to drive the sensor by an ac current and detect the response using the rectification technique. The combination of all these features has led to a SMR sensor with nearly zero dc offset and negligible hysteresis, and a detectivity around 1 nT/ √Hz at 1 Hz. 14 The performance is remarkable considering its extremely simple structure. However, in order to obtain a large field-like SOT effective field, in the previous studies, the NiFe layer thickness has been optimized to be around 1.8 nm. Such a small thickness of NiFe limits both the sensor's working field (±0.35 Oe) and operation temperature range (80 ⁰C), which may hinder practical application of the SMR sensor. Both issues, however, could be readily resolved if we can have a spin current and SOT generator which is more efficient than Pt and at the same time has a relatively low resistivity.Recently, several works have reported that alloying Pt with Au is an effective way to increase the SOT efficiency through enhancing the intrinsic spin Hall effect, 15,16 while the resistivity of AuxPt1-x alloy is still much lower than that of β-W, 17 β-Ta, 18 Pt-Hf alloy, 19 Pt/Hf multilayers 20 and topological insulators; 21,22 the latter is important for low-power operation of the sensor. In this work, we examine the possibility of using AuxPt1-x alloy to improve the working field and operation temperature range of the SMR sensors. Specifically, we fabricated

Oxygen incorporation has been reported to increase the current-induced spin-orbit torque in ferromagnetic heterostructures, but the underlying mechanism is still under active debate. Here, we report on an in-situ study of the oxygen exposure effect on spin-orbit torque in Pt/Co bilayers via controlled oxygen exposure, Co and Mg deposition, and electrical measurements in ultrahigh vacuum. We show that the oxygen exposure on Pt/Co indeed leads to an increase of spin-orbit torque, but the enhancement is not as large as those reported previously. Similar enhancement of spin-orbit torque is also observed after the deposition of an MgO capping layer. The results of ab initio calculations on the Rashba splitting of Pt/Co and Pt/Co/O suggest that the enhancement is due to enhanced Rashba-Edelstein effect by surface-adsorbed oxygen. Our findings shed some light on the varying roles of oxygen in modifying the spin torque efficiency reported previously.

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