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We report measurements of antiferromagnetic resonances in the van der Waals easy-axis antiferromagnet CrSBr. The interlayer exchange field and magnetocrystalline anisotropy fields are comparable to laboratory magnetic fields, allowing a rich variety of gigahertz-frequency dynamical modes to be accessed. By mapping the resonance frequencies as a function of the magnitude and angle of applied magnetic field, we identify the different regimes of antiferromagnetic dynamics. The spectra show good agreement with a Landau−Lifshitz model for two antiferromagnetically coupled sublattices, accounting for interlayer exchange and triaxial magnetic anisotropy. Fits allow us to quantify the parameters governing the magnetic dynamics: At 5 K, the interlayer exchange field is μ 0 H E = 0.395(2) T, and the hard and intermediate-axis anisotropy parameters are μ 0 H c = 1.30(2) T and μ 0 H a = 0.383(7) T. The existence of within-plane anisotropy makes it possible to control the degree of hybridization between the antiferromagnetic resonances using an in-plane magnetic field.

Spin–orbit torques (SOTs) that arise from materials with large spin–orbit coupling offer a new pathway for energy‐efficient and fast magnetic information storage. SOTs in conventional heavy metals and topological insulators are explored extensively, while 5d transition metal oxides, which also host ions with strong spin–orbit coupling, are a relatively new territory in the field of spintronics. An all‐oxide, SrTiO3 (STO)//La0.7Sr0.3MnO3 (LSMO)/SrIrO3 (SIO) heterostructure with lattice‐matched crystal structure is synthesized, exhibiting an epitaxial and atomically sharp interface between the ferromagnetic LSMO and the high spin–orbit‐coupled metal SIO. Spin‐torque ferromagnetic resonance (ST‐FMR) is used to probe the effective magnetization and the SOT efficiency in LSMO/SIO heterostructures grown on STO substrates. Remarkably, epitaxial LSMO/SIO exhibits a large SOT efficiency, ξ|| = 1, while retaining a reasonably low shunting factor and increasing the effective magnetization of LSMO by ≈50%. The findings highlight the significance of epitaxy as a powerful tool to achieve a high SOT efficiency, explore the rich physics at the epitaxial interface, and open up a new pathway for designing next‐generation energy‐efficient spintronic devices.

We adapt Sagnac interferometry for magneto-optic Kerr effect measurements of spin-orbit-torqueinduced magnetic tilting in thin-film magnetic samples. The high sensitivity of Sagnac interferometry permits for the first time optical quantification of spin-orbit torque from small-angle magnetic tilting of samples with perpendicular magnetic anisotropy (PMA). We find significant disagreement between Sagnac measurements and simultaneously-performed harmonic Hall (HH) measurements of spin-orbit torque on Pt/Co/MgO and Pd/Co/MgO samples with PMA. The Sagnac results for PMA samples are consistent with both HH and Sagnac measurements for the in-plane geometry, so we conclude that the conventional analysis framework for PMA HH measurements is flawed. We suggest that the explanation for this discrepancy is that although magnetic-field induced magnetic tilting in PMA samples can produce a strong planar Hall effect, when tilting is instead generated by spin-orbit torque it produces negligible change in the planar Hall signal. This very surprising result demonstrates an error in the most-popular method for measuring spin-orbit torques in PMA samples, and represents an unsolved puzzle in understanding the planar Hall effect in magnetic thin films.Spin-orbit torques (SOTs) [1, 2] are of interest for achieving high-efficiency manipulation of magnetization in magnetic memory technologies. SOTs are produced when a charge current is applied through a channel with strong spin-orbit coupling and generates a transverse spin current; this spin current can exert a spin-transfer torque on an adjacent ferromagnet (FM), allowing for low-power, electrical control of FM order. Memory cells with perpendicular magnetic anisotropy (PMA) are often preferred over their easy-plane counterparts because they may be fabricated at a higher density and are more resilient to stray magnetic fields or device heating. Accurate quantification of SOTs in PMA systems is therefore important for the development of future technologies.Several techniques are commonly used to quantify SOTs in PMA heterostructures [2-9], yet these methods often exhibit significant quantitative discrepancies with one another. The most-commonly-used method for PMA samples, the harmonic Hall (HH) technique, measures the strength of spin-orbit torques by using second-harmonic Hall signals to detect current-induced magnetic deflections relative to the out-of-plane orientation [3, 5,7]. This method is attractive for its simplicity and has been employed in hundreds of published papers, but it sometimes produces discrepancies and even clearly-unphysical torque values when applied to samples with relatively strong planar Hall effects [10][11][12][13][14][15]. Members of our research group have recently suggested that calculating SOTs from PMA HH measurements by ignoring the expected signal from the planar Hall effect provides results for the SOTs in better agreement with HH measurements on samples with in-plane anisotropy [15].Here, we test the influence of the planar Hall effect on HH meas...

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Spin-orbit torques generated by exfoliated layers of the low-symmetry semi-metal ZrTe 3 are measured using the spin-torque ferromagnetic resonance (ST-FMR) technique. When the ZrTe 3 has a thickness greater than about 10 nm, artifacts due to spin pumping and/or resonant heating can cause the standard ST-FMR analysis to overestimate the true magnitude of the torque efficiency by as much as a factor of 30, and to indicate incorrectly that the spin-orbit torque depends strongly on the ZrTe 3 layer thickness. Artifact-free measurements can still be achieved over a substantial thickness range by the method developed recently to detect ST-FMR signals in the Hall geometry as well as the longitudinal geometry. ZrTe 3 /Permalloy samples generate a conventional in-plane anti-damping spin torque efficiency 𝝃 DL || = 0.014 ± 0.004, and an unconventional in-plane field-like torque efficiency |𝝃 FL || | = 0.003 ± 0.001. The out-of-plane anti-damping torque is negligible. It is suggested that artifacts similarly interfere with the standard ST-FMR analysis for other van der Waals samples thicker than about 10 nm.

PACS 64.60.-i -First pacs description PACS 02.50.-r -Second pacs description PACS 05.45.-a -Third pacs description Abstract -We extend the theory of quasipotentials in dynamical systems by calculating, within a broad class of period-doubling maps, an exact potential for the critical fluctuations of pitchfork bifurcations in the weak noise limit. These far-from-equilibrium fluctuations are described by finitesize mean field theory, placing their static properties in the same universality class as the Ising model on a complete graph. We demonstrate that the effective system size of noisy period-doubling bifurcations exhibits universal scaling behavior along period-doubling routes to chaos.Period-doubling bifurcations have been observed in a wide variety of natural systems spanning many areas of science [1]. Univariate, discrete-time maps are the simplest dynamical systems to exhibit a period-doubling route to chaos [2,3]. Applications range from the population dynamics of species with non-overlapping generations [4,5] to the oscillations of rf-driven Josephson junctions [6,7]. The impact of noise on period-doubling maps has been extensively studied in both ecology [8][9][10][11] and physics [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], including the universal scaling of the Lyapunov exponent along period-doubling routes to chaos [31][32][33][34][35][36]. Connections between such noisy dynamical systems and the universality classes of equilibrium statistical physics has been a subject of great fascination [37][38][39][40][41][42][43][44][45][46][47][48][49]. The theory of quasipotentials, providing a formal link between equilibruim and nonequilibrium physics, has been applied to many systems [50,51]. In particular, the theory of quasipotentials has been used to estimate escape times from the attractors of noisy period-doubling maps [52][53][54] and to estimate the invariant probability distributions of their strange attractors in the chaotic regime [53,55,56].Here, we investigate the invariant probability distributions that characterize critical fluctuations in the pitchfork bifurcations of period-doubling maps far from the chaotic threshold. In the limit of weak noise, we find an exact correspondence between the static behavior of fluctuations at a pitchfork bifurcation and the critical behavior of finite-size mean field theory [57]. This correspondence places pitchfork bifurcations in the same universality class as the Ising model on a complete graph [58][59][60][61][62]. Analytical estimates of critical exponents and amplitudes agree well with the results of numerical simulations. We conclude with evidence of universal scaling behavior in the effective system size of critical fluctuations along period-doubling routes to chaos. p-1 arXiv:1502.04074v3 [cond-mat.stat-mech]