We describe Janus metal organic framework crystals that are propelled by bubble ejection. The Janus crystals are prepared by selective epitaxial growth of ZIF-67 on ZIF-8. The Janus crystals catalyse the decomposition of H2O2 into H2O and O2 on the ZIF-67 surface but not on the zinc containing ZIF-8 surface, resulting in propulsion of the Janus crystals.

We report measurements of current-induced thermoelectric and spin−orbit torque effects within devices in which multilayers of the semiconducting two-dimensional van der Waals magnet Cr 2 Ge 2 Te 6 (CGT) are integrated with Pt and Ta metal overlayers. We show that the magnetic orientation of the CGT can be detected accurately either electrically (using an anomalous Hall effect) or optically (using magnetic circular dichroism) with good consistency. The samples exhibit large thermoelectric effects, but nevertheless, the spin−orbit torque can be measured quantitatively using the angle-dependent second harmonic Hall technique. For CGT/Pt, we measure the spin−orbit torque efficiency to be similar to conventional metallic-ferromagnet/Pt devices with the same Pt resistivity. The interfacial transparency for spin currents is therefore similar in both classes of devices. Our results demonstrate the promise of incorporating semiconducting 2D magnets within spin−orbitronic and magneto-thermal devices.

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.

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...

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.