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1. Impact of strain on the SOT-driven dynamics of thin film Mn3Sn

   https://doi.org/10.1063/5.0179669  

   Shukla, Ankit; Qian, Siyuan; Rakheja, Shaloo (March 2024, Journal of Applied Physics)

   Mn 3 Sn, a metallic antiferromagnet with an anti-chiral 120° spin structure, generates intriguing magneto-transport signatures such as a large anomalous Hall effect, spin-polarized current with novel symmetries, anomalous Nernst effect, and magneto-optic Kerr effect. When grown epitaxially as MgO(110)[001]∥Mn3Sn(01¯1¯0)[0001], Mn3Sn experiences a uniaxial tensile strain, which changes the bulk sixfold anisotropy to a twofold perpendicular magnetic anisotropy (PMA). Here, we investigate the field-assisted spin–orbit-torque (SOT)-driven dynamics in single-domain Mn3Sn with PMA. We find that for non-zero external magnetic fields, the magnetic octupole moment of Mn3Sn can be switched between the two stable states if the input current is between two field-dependent critical currents. Below the lower critical current, the magnetic octupole moment exhibits a stationary state in the vicinity of the initial stable state. On the other hand, above the higher critical current, the magnetic octupole moment shows oscillatory dynamics which could, in principle, be tuned from the 100s of megahertz to the terahertz range. We obtain approximate analytic expressions of the two critical currents that agree very well with the numerical simulations for experimentally relevant magnetic fields. We also obtain a unified functional form of the switching time vs the input current for different magnetic fields. Finally, we show that for lower values of Gilbert damping (α≲2×10−3), the critical currents and the final steady states depend significantly on α. The numerical and analytic results presented in our work can be used by both theorists and experimentalists to understand the SOT-driven order dynamics in PMA Mn3Sn and design future experiments and devices. 

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2. Mechanical Resonant Sensing of Spin Texture Dynamics in a 2D Antiferromagnet

   https://doi.org/10.1002/adma.202420168  

   Yousuf, S_M_Enamul Hoque; Wang, Yunong; Ramachandran, Shreyas; Koptur‐Palenchar, John; Tarantini, Chiara; Xiang, Li; McGill, Stephen; Smirnov, Dmitry; Santos, Elton_J G; Feng, Philip X‐L; et al (July 2025, Advanced Materials)

   Abstract The coupling between the spin degrees of freedom and macroscopic mechanical motions, including striction, shearing, and rotation, has attracted wide interest with applications in actuation, transduction, and information processing. Experiments so far have established the mechanical responses to the long‐range ordered or isolated single spin states. However, it remains elusive whether mechanical motions can couple to a different type of magnetic structure, the non‐collinear spin textures, which exhibit nanoscale spatial variations of spin (domain walls, skyrmions,etc.) and are promising candidates to realize high‐speed computing devices. Here, collective spin texture dynamics is detected with nanoelectromechanical resonators fabricated from 2D antiferromagnetic (AFM) MnPS₃with 10⁻⁹strain sensitivity. By examining radio frequency mechanical oscillations under magnetic fields, new magnetic transitions are identified with sharp dips in resonant frequency. They are attributed to collective AFM domain wall motions as supported by the analytical modeling of magnetostriction and large‐scale spin‐dynamics simulations. Additionally, an abnormally large modulation in the mechanical nonlinearity at the transition field infers a fluid‐like response due to ultrafast domain motion. The work establishes a strong coupling between spin texture and mechanical dynamics, laying the foundation for electromechanical manipulation of spin texture and developing quantum hybrid devices. 

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3. Efficient Spin‐Orbit Torque Switching of the Semiconducting Van Der Waals Ferromagnet Cr ₂ Ge ₂ Te ₆

   https://doi.org/10.1002/adma.201906021  

   Ostwal, Vaibhav; Shen, Tingting; Appenzeller, Joerg (January 2020, Advanced Materials)

   Abstract Being able to electrically manipulate the magnetic properties in recently discovered van der Waals ferromagnets is essential for their integration in future spintronics devices. Here, the magnetization of a semiconducting 2D ferromagnet, i.e., Cr₂Ge₂Te₆, is studied using the anomalous Hall effect in Cr₂Ge₂Te₆/tantalum heterostructures. The thinner the flakes, hysteresis and remanence in the magnetization loop with out‐of‐plane magnetic fields become more prominent. In order to manipulate the magnetization in such thin flakes, a combination of an in‐plane magnetic field and a charge current flowing through Ta—a heavy metal exhibiting giant spin Hall effect—is used. In the presence of in‐plane fields of 20 mT, charge current densities as low as 5 × 10⁵A cm^–2are sufficient to switch the out‐of‐plane magnetization of Cr₂Ge₂Te₆. This finding highlights that current densities required for spin‐orbit torque switching of Cr₂Ge₂Te₆are about two orders of magnitude lower than those required for switching nonlayered metallic ferromagnets such as CoFeB. The results presented here show the potential of 2D ferromagnets for low‐power memory and logic applications. 

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4. Thermally generated spin current in the topological insulator Bi ₂ Se ₃

   https://doi.org/10.1126/sciadv.adi4540  

   Jain, Rakshit; Stanley, Max; Bose, Arnab; Richardella, Anthony R.; Zhang, Xiyue S.; Pillsbury, Timothy; Muller, David A.; Samarth, Nitin; Ralph, Daniel C. (December 2023, Science Advances)

   We present measurements of thermally generated transverse spin currents in the topological insulator Bi₂Se₃, thereby completing measurements of interconversions among the full triad of thermal gradients, charge currents, and spin currents. We accomplish this by comparing the spin Nernst magneto-thermopower to the spin Hall magnetoresistance for bilayers of Bi₂Se₃/CoFeB. We find that Bi₂Se₃does generate substantial thermally driven spin currents. A lower bound for the ratio of spin current density to thermal gradient is $\frac{J_s}{{\mathbf{\nabla }}_{\mathit{x}}\mathit{T}}$= (4.9 ± 0.9) × 10⁶ $\left(\frac{\hslash }{2e}\right)\frac{\mathbf{A}{\mathbf{m}}^{-2}}{\mathbf{K}\text{μ}{\mathbf{m}}^{-1}}$, and a lower bound for the magnitude of the spin Nernst ratio is −0.61 ± 0.11. The spin Nernst ratio for Bi₂Se₃is the largest among all materials measured to date, two to three times larger compared to previous measurements for the heavy metals Pt and W. Strong thermally generated spin currents in Bi₂Se₃can be understood via Mott relations to be due to an overall large spin Hall conductivity and its dependence on electron energy. 

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5. Ferrimagnetic Skyrmions in Topological Insulator/Ferrimagnet Heterostructures

   https://doi.org/10.1002/adma.202003380  

   Wu, Hao; Groß, Felix; Dai, Bingqian; Lujan, David; Razavi, Seyed_Armin; Zhang, Peng; Liu, Yuxiang; Sobotkiewich, Kemal; Förster, Johannes; Weigand, Markus; et al (July 2020, Advanced Materials)

   Abstract Magnetic skyrmions are topologically nontrivial chiral spin textures that have potential applications in next‐generation energy‐efficient and high‐density spintronic devices. In general, the chiral spins of skyrmions are stabilized by the noncollinear Dzyaloshinskii–Moriya interaction (DMI), originating from the inversion symmetry breaking combined with the strong spin–orbit coupling (SOC). Here, the strong SOC from topological insulators (TIs) is utilized to provide a large interfacial DMI in TI/ferrimagnet heterostructures at room temperature, resulting in small‐size (radius ≈ 100 nm) skyrmions in the adjacent ferrimagnet. Antiferromagnetically coupled skyrmion sublattices are observed in the ferrimagnet by element‐resolved scanning transmission X‐ray microscopy, showing the potential of a vanishing skyrmion Hall effect and ultrafast skyrmion dynamics. The line‐scan spin profile of the single skyrmion shows a Néel‐type domain wall structure and a 120 nm size of the 180° domain wall. This work demonstrates the sizable DMI and small skyrmions in TI‐based heterostructures with great promise for low‐energy spintronic devices. 

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