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1. Angular evolution of thickness-related unidirectional magnetoresistance in Co/Pt multilayers

   https://doi.org/10.1063/1.5079894  

   Oh, Junseok; Humbard, Levi; Humbert, Vincent; Sklenar, Joseph; Mason, Nadya (April 2019, AIP Advances)

   We report the magnetoresistance of Co/Pt superlattices having thickness gradients at different orientations relative to an applied current. We measure the magnetoresistance at a fixed field as a function of the out-of-plane field angle, and find a unidirectional magnetoresistance (UMR) in addition to the expected anisotropic magnetoresistance (AMR) and spin Hall magnetoresistance (SMR). Specifically, the UMR signal is the difference in resistance between the (out-of-plane) +z and −z field orientation. The magnitude of UMR is minimized when the thickness gradient is parallel to the applied current and maximized when the gradient is nearly perpendicular to the current. The results imply the possibility of an alternative source of UMR in Co/Pt multilayers in addition to the previously considered anomalous Hall effect. 

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2. Origins of observational errors in field sweep DC measurements for unidirectional magnetoresistance

   https://doi.org/10.1063/5.0127587  

   Fan, Yihong; Saha, Renata; Yang, Yifei; Wang, Jian-Ping (December 2022, Journal of Applied Physics)

   Understanding the mechanisms of unidirectional magnetoresistance (UMR) has become an important topic for its potential application of a two-terminal spin–orbit torque device. Field sweep DC measurements have been proposed and adopted to measure the value of UMR instead of second harmonic measurements. In this paper, potential measurement errors in conventional DC measurements are investigated. Oersted field and field-like torque usually do not influence the measurement, but a large field-like torque was found to lead to an anisotropic magnetoresistance difference when the sample is not perfectly aligned with the external field. The existence of ordinary magnetoresistance was also found to contribute to a large background. In this paper, an alternative measurement method for UMR was proposed and demonstrated to address those issues related to previous DC measurements. Our work may broaden the understanding of the error sources of UMR measurements and provide a reliable DC measurement method for the characterization of UMR. 

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3. Observation of unidirectional spin Hall magnetoresistance in amorphous PtSn ₄ /CoFeB bilayers

   https://doi.org/10.1063/5.0097355  

   Fan, Yihong; Cresswell, Zach; Guo, Silu; Zhang, Delin; Peterson, Thomas J.; Liu, Jinming; Lv, Yang; Andre Mkhoyan, K.; Wang, Jian-Ping (August 2022, Applied Physics Letters)

   Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10 −11 per A/cm 2 , 50% larger than reported values from heavy metals) in sputtered amorphous PtSn 4 /CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn 4 /CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices. 

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4. Probing antiferromagnetism in exfoliated Fe ₃ GeTe ₂ using magneto-transport measurements

   https://doi.org/10.1039/D3NR01022H  

   Chyczewski, Stasiu T.; Shi, Ji; Lee, Hanwool; Furlanetto, Paolo F.; Xu, Kai; van der Zande, Arend M.; Zhu, Wenjuan (August 2023, Nanoscale)

   Unique temperature dependences of the out-of-plane anomalous Hall effect and longitudinal magnetoresistance were observed, which can be attributed to the changing dominance between ferromagnetic and antiferromagnetic phases in the Fe₃GeTe₂sample. 

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5. Anisotropic and High‐Mobility Electronic Transport in a Quasi 2D Antiferromagnet NdSb ₂

   https://doi.org/10.1002/adfm.202308733  

   Singha, Ratnadwip; Yuan, Fang; Lee, Scott B.; Villalpando, Graciela V.; Cheng, Guangming; Singh, Birender; Sarker, Suchismita; Yao, Nan; Burch, Kenneth S.; Schoop, Leslie M. (November 2023, Advanced Functional Materials)

   Abstract Advancements in low‐dimensional functional device technology heavily rely on the discovery of suitable materials which have interesting physical properties as well as can be exfoliated down to the 2D limit. Exfoliable high‐mobility magnets are one such class of materials that, not due to lack of effort, has been limited to only a handful of options. So far, most of the attention has been focused on the van der Waals (vdW) systems. However, even within the non‐vdW, layered materials, it is possible to find all these desirable features. Using chemical reasoning, it is found that NdSb₂is an ideal example. Even with a relatively small interlayer distance, this material can be exfoliated down to few layers. NdSb₂has an antiferromagnetic ground state with a quasi 2D spin arrangement. The bulk crystals show a very large, non‐saturating magnetoresistance along with highly anisotropic electronic transport properties. It is confirmed that this anisotropy originates from the 2D Fermi pockets which also imply a rather quasi 2D confinement of the charge carrier density. Both electron and hole‐type carriers show very high mobilities. The possible non‐collinear spin arrangement also results in an anomalous Hall effect. 

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