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1. Controlling spin current polarization through non-collinear antiferromagnetism

   https://doi.org/10.1038/s41467-020-17999-4  

   Nan, T. ; Quintela, C. X. ; Irwin, J. ; Gurung, G. ; Shao, D. F. ; Gibbons, J. ; Campbell, N. ; Song, K. ; Choi, S. -Y. ; Guo, L. ; et al ( December 2020 , Nature Communications)

   null (Ed.)

   Abstract The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn 3 GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn 3 GaN/permalloy heterostructures can generate unconventional spin-orbit torques at room temperature corresponding to out-of-plane and Dresselhaus-like spin polarizations which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spin-orbit torque, enabling high-efficient antiferromagnetic spintronics. 

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2. Multiple magnetic droplet solitions from exotic spin–orbit torques

   https://doi.org/10.1063/5.0099491  

   Klause, Robin ; Hoffmann, Axel ( June 2022 , Applied Physics Letters)

   Materials with large spin–orbit interactions generate pure spin currents with spin polarizations parallel to the interfacial surfaces that give rise to conventional spin–orbit torques. These spin–orbit torques can only efficiently and deterministically switch magnets with in-plane magnetization. Additional symmetry breaking, such as in non-collinear antiferromagnets, can generate exotic, unconventional spin–orbit torques that are associated with spin polarizations perpendicular to the interfacial planes. Here, we use micromagnetic simulations to investigate whether such exotic spin–orbit torques can generate magnetic droplet solitions in out-of-plane magnetized geometries. We show that a short, high current pulse followed by a lower constant current can nucleate and stabilize magnetic droplets. Through specific current pulse lengths, it is possible to control the number of droplets in such a system, since torques are generated over a large area. Additionally, the nucleation current scales with the out-of-plane component of the spin polarization and is linear as a function of magnetic field strength. 

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3. High‐Efficiency Magnon‐Mediated Magnetization Switching in All‐Oxide Heterostructures with Perpendicular Magnetic Anisotropy

   https://doi.org/10.1002/adma.202203038  

   Zheng, Dongxing ; Lan, Jin ; Fang, Bin ; Li, Yan ; Liu, Chen ; Ledesma‐Martin, J. Omar ; Wen, Yan ; Li, Peng ; Zhang, Chenhui ; Ma, Yinchang ; et al ( July 2022 , Advanced Materials)

   The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron‐mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all‐oxide heterostructures of SrRuO₃/NiO/SrIrO₃are epitaxially grown on SrTiO₃single‐crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO₃with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO₃with strong spin–orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion‐related energy dissipation from electron‐mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all‐oxide spintronic devices operated by magnon current.

    

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4. Field-free deterministic switching of all–van der Waals spin-orbit torque system above room temperature

   https://doi.org/10.1126/sciadv.adk8669  

   Kajale, Shivam N ; Nguyen, Thanh ; Hung, Nguyen Tuan ; Li, Mingda ; Sarkar, Deblina ( March 2024 , Science Advances)

   Two-dimensional van der Waals (vdW) magnetic materials hold promise for the development of high-density, energy-efficient spintronic devices for memory and computation. Recent breakthroughs in material discoveries and spin-orbit torque control of vdW ferromagnets have opened a path for integration of vdW magnets in commercial spintronic devices. However, a solution for field-free electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room temperatures, essential for building compact and thermally stable spintronic devices, is still missing. Here, we report a solution for the field-free, deterministic, and nonvolatile switching of a PMA vdW ferromagnet, Fe₃GaTe₂, above room temperature (up to 320 K). We use the unconventional out-of-plane anti-damping torque from an adjacent WTe₂layer to enable such switching with a low current density of 2.23 × 10⁶A cm⁻². This study exemplifies the efficacy of low-symmetry vdW materials for spin-orbit torque control of vdW ferromagnets and provides an all-vdW solution for the next generation of scalable and energy-efficient spintronic devices.

    

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5. Tuning Spin‐Orbit Torques Across the Phase Transition in VO 2 /NiFe Heterostructure

   https://doi.org/10.1002/adfm.202111555  

   Kim, Jun‐young ; Cramer, Joel ; Lee, Kyujoon ; Han, Dong‐Soo ; Go, Dongwook ; Salev, Pavel ; Lapa, Pavel N. ; Vargas, Nicolas M. ; Schuller, Ivan K. ; Mokrousov, Yuriy ; et al ( January 2022 , Advanced Functional Materials)

   The emergence of spin‐orbit torques as a promising approach to energy‐efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin‐orbit torques. Here, current‐induced spin‐orbit torques in VO₂/NiFe heterostructures are investigated using spin‐torque ferromagnetic resonance, where the VO₂layer undergoes a prominent insulator‐metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO₂/NiFe interface spin absorption across the VO₂phase transition. More remarkably, a large modulation (±100%) and a sign change of the current‐induced spin‐orbit torque across the VO₂phase transition suggest two competing spin‐orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO₂, corroborated by the first‐principles calculation of the spin Hall conductivity , is verified as the main source of the spin‐orbit torque in the metallic phase. The self‐induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO₂, can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin‐orbit torques of materials that undergo phase transitions for new device functionalities.

    

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