Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B38: Magneto-Transports and Magnetic InterfacesFocus Live
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Sponsoring Units: GMAG DMP FIAP Chair: See-Hun Yang, IBM Almaden Research Center |
Monday, March 15, 2021 11:30AM - 11:42AM Live |
B38.00001: Large and local magnetoresistance in a state-of-the-art perpendicular magnetic medium Morgan C Williamson, Cheng Wang, Pin-Wei Huang, Ganping Ju, Maxim Tsoi
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Monday, March 15, 2021 11:42AM - 11:54AM Live |
B38.00002: Longitudinal and transverse unidirectional magnetoresistances driven by interfacial spin-orbital scattering M. Mehraeen, Pengtao Shen, Shulei Zhang The recent observation of the unidirectional spin Hall magnetoresistance (USMR) -- a longitudinal magnetoresistance that changes sign with the reversal of either the in-plane electric field or the magnetization -- in ferromagnetic and heavy metal bilayers has led to increased interest in the study of nonlinear magnetotransport effects. Here, we predict both longitudinal and transverse unidirectional magnetoresistances in magnetic layered structures, which do not rely on the spin Hall effect but instead arise from the concerted actions of interfacial Rashba spin-orbit coupling and spin-dependent scattering. We analyze the nonlinear magnetotransport using both a semiclassical Boltzmann equation approach and a full quantum mechanical approach and will discuss the dependence of the proposed effect on quantum coherence, interface property as well as the thicknesses of the layers. |
Monday, March 15, 2021 11:54AM - 12:06PM Live |
B38.00003: Linear and Nonlinear Two-Terminal Spin-Valve Effect from Chirality-Induced Spin Selectivity Tianhan Liu, Xiaolei Wang, Hailong Wang, Eric Lochner, Pedro Schlottmann, Stephan Von Molnar, Jianhua Zhao, Peng Xiong Electrical generation of spin polarization in nonmagnetic materials is of broad interest for the underlying physics and device potential. One such scheme is chirality-induced spin selectivity (CISS), with which structural chirality leads to different electric conductivities for electrons of opposite spins. CISS has been reported for many chiral structures on different surfaces. However, the microscopic origin and transport mechanisms remain controversial. In particular, the fundamental Onsager relation was argued to preclude linear-response detection of CISS by a ferromagnet. Here, we report definitive observation of CISS-induced magnetoconductance in vertical heterojunctions of (Ga,Mn)As/AHPA-L molecules/Au, directly verifying spin filtering by the AHPA-L molecules via spin detection by the (Ga,Mn)As.1 The pronounced and robust magnetoconductance signals enable a rigorous examination of its bias dependence, which shows both linear- and nonlinear-response components. The definitive identification of the linear-response CISS-induced two-terminal spin-valve effect places an important constraint for a viable theory of CISS and its device manifestations. |
Monday, March 15, 2021 12:06PM - 12:42PM Live |
B38.00004: Electrical Switching of Antiferromagnetic FexNbS2 driven by the collective dynamics of a coexisting spin glass Invited Speaker: Eran Maniv Advances in controlling electron correlations in transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics — a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk. The theory behind the electrical switching of antiferromagnets is premised on the existence of a well-defined broken symmetry state that can be rotated to encode information. A spin glass is in many ways the antithesis of this state, characterized by an ergodic landscape of nearly degenerate magnetic configurations, freezing into its final distribution in a manner that is seemingly bereft of information. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B38.00005: Evidence for ideal memristive functionality in ferromagnet/antiferromagnet nanostructures revealed by spin Hall effect-driven harmonic measurements Sergei Ivanov, Sergei Urazhdin Viscous dynamics was suggested to enable ideal memristive functionality in neuromorphic applications [1]. However, nanodevice implementation requires efficient electronic driving and sensing of viscous dynamics, which have not yet been realized. We study thin-film Pt/Permalloy(Py)/CoO nanostrips to demonstrate the possibility to drive viscous magnetization dynamics of Permalloy by the current-driven spin Hall effect in Pt and the Oersted field and detect it using the anisotropic magnetoresistance. We utilize ac current driving and detection at the second harmonic produced by mixing between ac current and resistance oscillations due to magnetization oscillations. The viscous dynamics is signified by a large imaginary part of the dynamic response at temperatures somewhat above the onset of exchange bias, consistent with the viscous dynamics of the correlated spin liquid state in CoO recently demonstrated for CoO/Py bilayers by the transverse ac susceptibility technique [2]. Our approach is amenable to downscaling and to efficient ideal memristor implementations. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B38.00006: Observation of magnetoelastic Gilbert damping in highly magnetostrictive Fe0.7Ga0.3 thin films William Peria, Heshan Yu, Seunghun Lee, Ichiro Takeuchi, Paul A Crowell Gilbert damping remains among the foremost properties when considering the design of spintronics devices. There are many cases where the observed damping is larger than the predicted damping, which is usually based on considerations of electronic structure (like the Kamberský torque-correlation model [1]). Here we report a large magnetoelastic contribution to the Gilbert damping in highly magnetostrictive Fe0.7Ga0.3 thin films, which grows to as large as 6 times greater than the intrinsic damping at 50 K. To show this, we present the orientational and temperature dependence of the Gilbert damping. The mechanism is suppressed for out-of-plane magnetization due to confinement effects from the interfaces of the film, leading to a large anisotropy. The damping for in-plane magnetization also increases significantly at low temperatures due to the increasing magnetoelastic energy. We conclude by emphasizing that, in general, the magnetoelastic damping may constitute a significant portion of the total Gilbert damping, particularly in materials with high magnetostriction. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B38.00007: Chirality induced spin selectivity through time-reversal symmetric helical molecular junctions Yasuhiro Utsumi, Ora Entin-Wohlman, Amnon Aharony Time-reversal symmetric charge and spin transport through a molecule comprising two-orbital channels and connected to two leads is analyzed. It is demonstrated that spin-resolved currents are generated when spin-flip processes are accompanied by a flip of the orbital channels. This finding does not contradict Bardarson's theorem [J. Phys. A 41, 405203 (2008)]: The transmission eigen values are doubly degenerate. The spin-filtering effect is explicitly demonstrated for a two-terminal chiral molecular junction, modeled by a two-orbital helical tight-binding chain with intra-atomic spin-orbit interactions (SOI). In the context of transport through DNA, this effect is termed chirality-induced spin selectivity (CISS). The model exhibits spin splitting without breaking time-reversal symmetry: the intra-atomic SOI induces concomitant spin and orbital flips. Examining these transitions from the point of view of the Bloch states in an infinite molecule, it is shown that they cause shifts in the Bloch wave numbers, of the size of the reciprocal single turn, whose directions depend on the left and right handedness of the helix. As a result, spin-up and -down states propagate in the opposite directions, leading to the CISS effect [Utsumi, Entin-Wohlman, and Aharony, PRB 102, 035445 (2020)]. |
Monday, March 15, 2021 1:18PM - 1:30PM Live |
B38.00008: Non-charge-carrier-mediated spin-transport in an organic semiconductor Henna Popli, Jingying Wang, Xiaojie Liu, Evan Lafalce, Taniya Hansika Tennahewa, Hans Malissa, Valy Vardeny, Christoph M Boehme We report experiments scrutinizing existing theoretical pictures of spin-transport in organic thin films, based on the idea that this is due to the same mechanisms as charge transport [1, 2], as it is the case for many inorganic materials. Experimentally, we used the inverse spin-Hall effect (ISHE) in thin Pt films [3] to detect pure spin currents in adjacent organic semiconductor (Alq3) layers, caused by ferromagnetic resonance driven spin-pumping of NiFe layers. To verify the involvement of charge carrier spins, the IISHE is expected to vanish when the charge carrier spins in Alq3 are magnetic resonantly scrambled [4]. No such quenching of IISHE is observed though within the given noise thresholds, indicating that spin-transport is neither due to charge carriers propagation nor due to spin-spin coupling. We discuss our experimental findings and various control measurements to corroborate the results. [1] M. Groesbeck et al. Phys. Rev. Letts. 124, 067702 (2020); [2] Z. Yue et al., Phys. Rev. B 92, 045405 (2015); [3] K. Ando et al. Nat. Phys. 12, 622 (2013); [4] H. Popli et al. Phys. Rev Appl. 14, 034012 (2020). |
Monday, March 15, 2021 1:30PM - 1:42PM Live |
B38.00009: Substrate Effects on Spin Lattice Relaxation in the Molecular Qubit CuPc Kathleen Mullin, James M Rondinelli Molecular magnets can serve as qubits for quantum information system (QIS) applications where the molecule’s electron spin is used for storing information. To be functional in QIS applications, regular arrays of qubits supported on substrates need to exhibit long relaxation times. To address this challenge, we performed electronic structure calculations on a substrate-supported molecular magnet system, comprising copper(II) phthalocyanine(CuPc) on graphene, and examined changes in relaxation times using a spin lifetime proxy. We discuss how CuPc mechanically couples to graphene and what effect this coupling has on the molecule’s electronic structure and magnetic state. We compute the local vibrational modes for CuPc with and without graphene at the density functional theory level, and then, use these vibrational modes to calculate the variation in the g-tensor (our proxy for spin-lattice relaxation) for the molecule. Lastly, we analyze the changes in the g-tensor to understand how the coupling between the molecule and the surface will contribute to the spin-lattice relaxation times for the coupled substrate-qubit system. |
Monday, March 15, 2021 1:42PM - 1:54PM Live |
B38.00010: Temperature dependence of shot noise in double barrier magnetic tunnel junctions Jiasen Niu, Liang Liu, Jiafeng Feng, Xiufeng Han, J M D Coey, Xiaoguang Zhang, Jian Wei Shot noise reveals spin dependent transport properties in a magnetic tunnel junction. We report measurement of shot noise in CoFeB/MgO/CoFeB/MgO/CoFeB double barrier magnetic tunnel junctions, which shows a strong temperature dependence. The Fano factor used to characterize shot noise increases with decreasing temperature. A sequential tunneling model can be used to account for these results, in which a larger Fano factor results from larger spin relaxation length at lower temperatures. |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B38.00011: ac Hanle effect in spin valves Yaroslaw Bazaliy It is known [1] that the ac spin current flowing through FNF spin valves produces results similar to those of the Hanle effect. In such case the current frequency plays the role of the external magnetic field. We study the combination of the two effects: an ac Hanle effect in spin valves and find that it results in new types of signatures in the non-local voltage dependencies. |
Monday, March 15, 2021 2:06PM - 2:18PM Live |
B38.00012: Magnetic and Electron-Transport Properties of Co2Si Nanomagnets Rabindra Pahari, Balamurugan Balasubramanian, Tom A. George, Priyanka Manchanda, Ahsan Ullah, Ralph Skomski, David J Sellmyer Magnetic and spin-transport properties of nanostructured materials have attracted much attention in the context of spintronic devices [1, 2]. In this work, we investigate ferromagnetism and magnetotransport in thin films of Co2Si nanoclusters experimentally and theoretically. The nanoclusters form an orthorhombic structure (space group: Pnma) and have an average size d ≈ 11.3 nm with a standard deviation of σ/d ≈ 0.19. The nanoclusters exhibit room-temperature ferromagnetism with a substantial saturation magnetization of 0.70 μB/Co at 10 K and 0.49 μB/Co at 300K. On decreasing temperature from 300 K, the nanoclusters show electron-transport properties unusual for a ferromagnetic metal, including an increase of Hall resistivity and a non-monotonic change of negative magnetoresistance with a peak at around 100 K. The underlying physics is explained on the basis of the large polarization of surface spins and variation in the degree of their misalignments due to temperature-dependent effective anisotropy [3]. |
Monday, March 15, 2021 2:18PM - 2:30PM On Demand |
B38.00013: Current-induced unidirectional magnetoresistance in Pt/FeRh bilayers Julie Shim, Hilal Saglam, Jonathan Gibbons, Junseok Oh, Yi Li, Wei Zhang, Shulei Zhang, Axel F Hoffmann, Joseph N Sklenar, Nadya Mason The unidirectional magnetoresistance (UMR) effect has garnered considerable interest since it can provide fundamental insight into the transport properties of spin-orbit coupled systems. The origin of the UMR in ferromagnet and non-magnetic bilayers has been actively studied [1,2] but experimental investigations of the UMR in metallic antiferromagnet and non-magnetic bilayers are lacking. |
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