Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T57: Spin Transport and Dynamics in AntiferromagnetsFocus
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Sponsoring Units: GMAG Chair: Soho Shim, University of Illinois at Urbana-Champaign Room: Room 303 |
Thursday, March 9, 2023 11:30AM - 12:06PM |
T57.00001: Vector Spin Seebeck Effect in antiferromagnet LuFeO3 with canted spins Invited Speaker: Jiaming He The generation, detection and manipulation of spins are imperative for spintronics research and applications. The spin injection through the spin Seebeck effect (SSE), typically done on magnets with collinear moments, is always along the out-of-plane direction. Here, we report the observation of a vector SSE effect in antiferromagnet (AF) LuFeO3 with canted spins. The temperature gradient applied along out-of-plane on the c-axis as well as in ab-plane directions both inject spin current from AF insulator into the heavy metal layer and voltage generated by inverse spin Hall effect can be detected. We show that the detected thermovoltages are related to the canted spin structure of LuFeO3 and are viable in zero magnetic field. Both the canted spin direction and the sign of the detected thermovoltages can be controlled by a small magnetic field at around 150 Oe at room temperature. [1] These results have been compared with that from a similar experiment on LaFeO3. [2] This class of AF insulators broaden the scope for exploring spin phenomena and provide a new class of material for low-field antiferromagnetic spin caloritronics. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T57.00002: Spin-Orbit Torques in Non-Collinear Antiferromagnet Mn3Pt Robin Klause, Saima A Siddiqui, Axel Hoffmann Mn3Pt is a non-collinear antiferromagnet with an fcc crystal structure and magnetic moments on the Mn atoms that are at an angle of 120° with respect to each other. This arrangement breaks the cubic symmetry and leaves only one mirror symmetry axis, which allows for the existence of the anomalous Hall effect and exotic spin-orbit torques. Here we measure the anomalous Hall effect that emerges at temperatures below 270 K, where the Mn3Pt undergoes a magnetic transition from a collinear phase at higher temperatures to a non-collinear phase at lower temperatures. This transition is accompanied by a sudden change in resistance. Moreover, because of the symmetry breaking, we expect Mn3Pt to generate exotic spin accumulations with an out-of-plane component at the interface with a ferromagnet. We explore the full symmetries of the spin-orbit torques by performing spin-torque ferromagnetic resonance and second harmonic Hall measurements as a function of magnetic field orientation. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T57.00003: Effect of heat diffusion on current-driven magnetization switching in non-collinear antiferromagnets Myoung-Woo Yoo, Virginia O Lorenz, David G Cahill, Axel Hoffmann Non-collinear antiferromagnets (AFs) are interesting for spintronics [1], since they exhibit large anomalous Hall and magneto-optical Kerr effects, which can be used for detecting their magnetic order [2]. Furthermore, their magnetic order can be modulated electrically by spin-orbit torques [3]. The magnetization switching requires a temperature sufficiently close to the Néel temperature [4]. However, the temperature by Joule heating is dependent on heat diffusion by adjacent substrates. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T57.00004: Phase control of a coherent magnon excitation in a van der Waals antiferromagnet Jonathon W Kruppe, Shingo Toyoda, James Analytis, Joseph W Orenstein Magnon excitations in antiferromagnets have recently become the focus of both fundamental studies in magnetism, as well as the effort to establish new platforms for next-generation spintronic devices. While magnons are characterized by an amplitude, frequency, and phase, control over only the first two properties has been widely demonstrated. Complete control of the phase has remained elusive, imposing limitations on the manipulation of magnons for further applications. Here, we report a phase controlled coherent magnon excitation in a van der Waals antiferromagnet NiPS_3 using an optical pump-probe measurement. The presence of both linearly and circularly polarized pump-induced excitations enables full phase control with the pump helicity. The ability to control the initial phase of the magnon excitation has promise for both fundamental studies, such as the creation of a transient phase grating, as well as in spintronic applications in spin-wave phased arrays and spin-based terahertz technology. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T57.00005: Van der Waals Spin-Orbit Torque Antiferromagnetic Memory Lishu Zhang, LEI SHEN, Yuan-Ping Feng Modern magnetic random-access memory (MRAM) technology requires all-electric control of magnetization with high speed and low energy consumption. Here, we design field-free spin-orbit torque (SOT) MRAM using a two-dimensional Van der Waals heterostructure with antiferromagnetic bilayer LaBr2 and inversion asymmetric monolayer Td-WTe2. Our calculations, combining density functional theory with nonequilibrium Green function methods and micromagnetic simulations, show that the proposed SOT device has a low critical current density and can achieve field-free and very fast switching of magnetization, which makes excellent writing operation. It also has sensitive reading ability due to a high tunnel magnetoresistance ratio up to 1200%. Our work offers new opportunities for 2D spin-orbitronics. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T57.00006: Sub-Nanosecond Electrical Pulse Switching of an Easy Plane Antiferromagnetic Insulator Justin J Michel, Jose Flores, Fengyuan Yang Antiferromagnetic insulators (AFIs) are a promising candidate for new high speed magnetic memory materials. If the current-induced Néel order switching that has been previously observed in heavy-metal/AFI bilayers is due to spin orbit torques, this promises the ability to manipulate these materials at a much higher frequency than is currently allowed by intrinsic limits in ferromagnet-based memory. However, there is still considerable debate about the mechanism of the observed switching, as previous reports show a significant contribution from the relatively slow thermally-induced magnetoelastic effect in the quasi-dc pulse width regime. Here we report reliable current-induced switching of the easy plane antiferromagnet Hematite (α-Fe2O3) with a Platinum overlayer down to 300 ps. We examine the switching threshold dependence as a function of electrical pulse width, which strongly indicates that in this regime spin orbit torques are the dominant mechanism, reaffirming antiferromagnetic spintronic devices as a promising new system for high-frequency applications. |
Thursday, March 9, 2023 1:06PM - 1:18PM Author not Attending |
T57.00007: Control of Néel Vector with Spin-Orbit Torques in an Antiferromagnetic Insulator with Tilted Easy Plane Pengxiang Zhang, Chung-Tao Chou, Hwanhui Yun, Brooke C McGoldrick, Justin T Hou, Andre Mkhoyan, Luqiao Liu Electrical manipulation of spin textures inside antiferromagnets represents a new opportunity for developing spintronics with superior speed and high device density. Injecting spin currents into antiferromagnets and realizing efficient spin-orbit-torque-induced switching is however still challenging. Because of the diminishing magnetic susceptibility, the nature and the magnitude of current-induced magnetic dynamics remain poorly characterized in antiferromagnets, whereas spurious effects further complicate experimental interpretations. In this work, by growing a thin film antiferromagnetic insulator, α-Fe2O3, along its non-basal plane orientation, we realize a configuration where an injected spin current can robustly rotate the Néel vector within the tilted easy plane, with an efficiency comparable to that of classical ferromagnets. The spin-orbit torque effect stands out among other competing mechanisms and leads to clear switching dynamics. Thanks to this new mechanism, in contrast to the usually employed orthogonal switching geometry, we achieve bipolar antiferromagnetic switching by applying positive and negative currents along the same channel, a geometry that is more practical for device applications. By enabling efficient spin-orbit torque control on the antiferromagnetic ordering, the tilted easy plane geometry introduces a new platform for quantitatively understanding switching and oscillation dynamics in antiferromagnets. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T57.00008: Cavity-mediated coupling of terahertz antiferromagnetic spin waves in distant crystals Marcin Bialek, Jean-Philippe Ansermet In the regime of strong light-matter coupling, polariton modes are formed that are hybrid light-matter excitations sharing properties of both, an electrodynamic cavity mode and a matter mode. In the recent decade, magnon-polaritons were intensively researched using ferromagnetic materials in the microwave range, with potential applications for quantum technology and sensors. Exploring antiferromagnetic resonance (AFMR) rises magnon-polariton frequencies into the terahertz (THz) range. Here, we are investigating AFMR in hematite (α-Fe2O3) owing to its very low spin damping and temperature-dependent frequency above room temperature. We report on coupling of AFMR in two parallel-plane crystal slabs placed next to each other at a well controlled gap, forming a tunable Fabry-Perot type cavity. Frequency of AFMR in each crystal was indepently controlled by changing its temperature. Thus, as a function of temperature difference between the slabs, one expects to observe a crossing of AFMRs from both crystals. We used a continuous-wave spectrometer operating in the range of 0.2-0.35 THz, which is based on a frequency extender to a vector network analyzer. In reflection spectra, collected as a function of temperature difference between the two crystals, we observed avoided crossings of cavity modes and AFMRs from both slabs. Frequencies of cavity modes can be controlled by changing the gap between the crystals. For distances such that one of cavity modes has a frequency close to the crossing point between the AFMRs from both slabs, we observe that they hybridize by showing avoided crossings. This cavity-mediated coupling softens with rising gap between the crystals and is observable up to almost 9 mm, that is 10 times the sum of crystal slabs thicknesses (0.9 mm). We explain our results using classical electrodynamics and a model based on the input-output theory. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T57.00009: Observation of Spin-Splitter Torque in Collinear Antiferromagnetic RuO2 Shutaro Karube, Takahiro Tanaka, Daichi Sugawara, Naohiro Kadoguchi, Makoto Kohda, Junsaku Nitta The spin-splitter effect is theoretically predicted to generate an unconventional spin current with x- and z- spin polarization via the spin-split band in antiferromagnets. The generated torque, namely, spin-splitter torque, is effective for the manipulation of magnetization in an adjacent magnetic layer without an external magnetic field for spintronic devices such as MRAM. Here, we study the generation of torque in collinear antiferromagnetic RuO2 with (100), (101), and (001) crystal planes. Next we find all x-, y-, and z-polarized spin currents depending on the Néel vector direction in RuO2(101). For RuO2(100) and (001), only y-polarized spin current was present, which is independent of the Néel vector. Using the z-polarized spin currents, we demonstrate field-free switching of the perpendicular magnetized ferromagnet at room temperature. The spin-splitter torque generated from RuO2 is verified to be useful for the switching phenomenon and paves the way for a further understanding of the detailed mechanism of the spin-splitter effect and for developing antiferromagnetic spin-orbitronics. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T57.00010: Magneto-Optic Measurement of Surface Spin Accumulation in RuO2 Resulting from Spin-Split Band Structure Joongwon Lee, Sreejith Thampan Nair, Rakshit Jain, Daniel C Ralph, Bharat Jalan, Farhan Rana Spin transport in topological insulators and antiferromagnets have been extensively studied for spintronic applications due to their potential of providing larger spin Hall angle than conventional spin Hall metals, such as Pt or W. The two collinear spin sublattices in the rutile crystal structure of the metal antiferromagnet RuO2 are related by time reversal and a 90-degree lattice rotation with respect to the c-axis [1]. Such crystallographic and magnetic structure give rise to a spin-split band structure and results in the generation of a spin current in the presence of a charge current with spin polarization parallel to the Néel vector. Spin Hall angle in RuO2 is theoretically [2] shown to be larger than Pt and W. Suitable canting of the Néel vector can result in a surface spin accumulation with a strong out-of-plane spin component which allows optical detection of the spins via the magneto-optic Kerr effect (MOKE). In this work, we use MOKE with a high sensitivity of 28 nrad/√Hz to experimentally study the spin Hall effect in RuO2. Our results show that RuO2 exhibits Kerr signals as large as 100 nrad in the presence of a charge current. Results from different crystal orientations and different directions of charge current flow will be presented along with estimates for the accumulated spin densities. Thermally induced effects will also be discussed. [1] Phys. Rev. Lett. 118, 077201 (2017), [2] Phys. Rev. Lett. 126, 127701 (2021). |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T57.00011: Antiferromagnetic magnetostriction effect in uniaxial antiferromagnet revealed by magnetoresistance probe Haoyu Liu, Junxue Li, Wei Yuan, Jing Shi Antiferromagnetic materials are expected to play an important role in future spintronic applications thanks to their unique properties, such as robustness against perturbation and terahertz-frequency spin dynamics. However, detection, along with efficient manipulation, of antiferromagnetic order parameter remain to be challenging. In analogy to the ferromagnetic case, spin-Hall magnetoresistance in antiferromagnets has been proposed to detect antiferromagnetic order. Here, we have carried out a systematic study of the magnetoresistance in uniaxial antiferromagnet Cr2O3/normal metal heterostructures. By sweeping the external magnetic field, we observed a jump in the magnetoresistance at the spin-flop transition due to the sudden rotation of the Néel order with respect to the current direction. More surprisingly, the jump persists even when a 5nm Al2O3 layer is inserted between Pt and Cr2O3, which indicates that, in addition to the expected spin-Hall magnetoresistance, the antiferromagnetic magnetostriction effect is also present at the spin-flop transition of the uniaxial antiferromagnet Cr2O3 system. Our findings suggest that magnetoresistance measurement in the adjacent metal layer serves as a convenient probe to detect both magnetostriction coefficients and antiferromagnetic order parameter. |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T57.00012: Magnetic field induced room temperature spin nematicity in tetragonal antiferromagnetic FeTe thin films grown by molecular beam epitaxy Connie H Li, Jisoo Moon, Qiang Zou, Olaf M Van T Erve, Lian Li Iron chalcogenide FeTe is the parent compound of superconducting iron chalcogenides. It exhibits a spontaneous double-stripe bicollinear antiferromagnetic (AFM) order whose Néel temperature (TN) coincides with the temperature of a structural transition from tetragonal to monoclinic lattice distortion. For bulk materials, recent in-plane angular-dependent magnetoresistance measurement has further revealed a magnetic-?eld-induced spin nematicity at 110 K, above the antiferromagnetic ordering TN. In this work, we report similar spin-nematicity in epitaxial FeTe thin films, which persists up to room temperature. The FeTe films were grown on SrTiO3(001) substrates by molecular beam epitaxy, which exhibits a layer-by-layer growth as verified by in-situ scanning tunneling microscopy. The AFM order is confirmed by superconducting quantum interference device magnetometry with a TN of 75 K. Transport measurements indicate p-type carrier from room temperature to 2 K with a mobility of 2,162 cm2/V·s at low temperature, which is three orders of magnitude higher than those previously reported in this material system. Anisotropic magnetoresistance measurements reveal a two-fold anisotropy under rotating in-plane magnetic fields up to 9 T. The anisotropy persists up to room temperature, indicating magnetic field induced spin nematicity above TN. |
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