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We demonstrate nondecaying, steplike electrical switching of tristate N\'eel order in $\mathrm{Pt}/\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ bilayers detected by the spin-Hall induced anomalous Hall effect. The as-grown $\mathrm{Pt}/\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ bilayers exhibit sawtooth switching behavior generated by current pulses. After annealing by a high pulse current, the Hall signals reveal single-pulse saturated, nondecaying, steplike switching. Together with control experiments, we show that the sawtooth switching is due to an artifact of Pt while the actual spin-orbit torque induced antiferromagnetic switching is steplike. Our Monte Carlo simulations explain the switching behavior of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ N\'eel order among three in-plane easy axes.

The topological Hall effect has been a primary indicator of nontrivial spin textures in magnetic materials. We observe the evidence of the topological Hall effect in $\mathrm{Pt}/{\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ bilayers grown on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(0001)$ and ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(11\overline{2}0)$, where the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ epitaxial film is an antiferromagnetic insulator. The $\mathrm{Pt}/{\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ bilayers exhibit topological Hall resistivity for ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ thicknesses below 6 nm near and above room temperature, which is above the N\'eel temperature of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, revealing the key role of thermal fluctuations in the formation of spin textures. The similarity of topological Hall signals in (0001)- and $(11\overline{2}0)$-oriented ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ films indicates that the emergence of spin textures is insensitive to crystalline orientation.

Noncollinear antiferromagnet Mn3Sn has attracted wide interest as it is a candidate for Weyl semimetal. Here, we report the observation of topological Hall like signals in Mn3Sn/Pt bilayers grown on Al2O3(0001). X-ray diffraction and scanning transmission electron microscopy results confirm the high epitaxial quality of the c-axis-oriented Mn3Sn films. The detected topological Hall resistivity shows a broad temperature range from 210 to 365 K by tuning the thickness of Mn3Sn from 3 to 15 nm. Compared with previously reported topological Hall effects in Mn3Sn at temperatures below 50 K, the observed high-temperature topological Hall signal is likely due to the stabilization of topological spin textures enabled by the strong spin–orbit coupling of the Pt overlayer and the Dzyaloshinskii–Moriya interaction at the Mn3Sn/Pt interface.

We report spin-echo double resonance NMR measurements of {sup 17}O- {sup 63} Cu indirect (electron-mediated) nuclear spin-spin coupling between Cu and O atoms in the CuO{sub 2} planes of YBa{sub 2}Cu {sub 3}O{sub 7} . The magnitude of the measured coupling is anomalously large, to the extent that it is inconsistent with the antiferromagnetic correlations that are invoked to explain the contrasting T{sub 1} behaviors of {sup 63}Cu and {sup 17}O . {copyright} {ital 1999} {ital The American Physical Society }

We report a simple NMR experiment measuring individual ${}^{63}\mathrm{Cu}\ensuremath{-}{}^{63}\mathrm{Cu}$ indirect nuclear coupling frequencies in $\mathrm{YBa}{}_{2}\mathrm{Cu}{}_{3}{\mathrm{O}}_{7}$. We show that the coupling interaction at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\mathrm{K}$ is of quite short range, indicating an anitferromagnetic correlation length $\ensuremath{\xi}$ of $\ensuremath{\sim}1$ lattice constant or less.