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Register a new userDirect Imaging of Electrical Switching of Antiferromagnetic Neel Order in $alpha$-Fe$_2$O$_3$ Epitaxial Films
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We report the direct observation of switching of the Neel vector of antiferromagnetic (AFM) domains in response to electrical pulses in micron-scale Pt/$alpha$-Fe$_2$O$_3$ Hall bars using photoemission electron microscopy. Current pulses lead to reversible and repeatable switching, with the current direction determining the final state, consistent with Hall effect experiments that probe only the spatially averaged response. Current pulses also produce irreversible changes in domain structure, in and even outside the current path. In both cases only a fraction of the domains switch in response to pulses. Further, analysis of images taken with different x-ray polarizations shows that the AFM Neel order has an out-of-plane component in equilibrium that is important to consider in analyzing the switching data. These results show that -in addition to effects associated with spin-orbit torques from the Pt layer, which can produce reversible switching-changes in AFM order can be induced by purely thermal effects.
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The ability to manipulate antiferromagnetic (AF) moments is a key requirement for the emerging field of antiferromagnetic spintronics. Electrical switching of bi-state AF moments has been demonstrated in metallic AFs, CuMnAs and Mn$_2$Au. Recently, current-induced saw-tooth shaped Hall resistance was reported in Pt/NiO bilayers, while its mechanism is under debate. Here, we report the first demonstration of convincing, non-decaying, step-like electrical switching of tri-state Neel order in Pt/$alpha$-Fe$_2$O$_3$ bilayers. Our experimental data, together with Monte-Carlo simulations, reveal the clear mechanism of the switching behavior of $alpha$-Fe$_2$O$_3$ Neel order among three stable states. We also show that the observed saw-tooth Hall resistance is due to an artifact of Pt, not AF switching, while the signature of AF switching is step-like Hall signals. This demonstration of electrical control of magnetic moments in AF insulator (AFI) films will greatly expand the scope of AF spintronics by leveraging the large family of AFIs.
We probe the current-induced magnetic switching of insulating antiferromagnet/heavy metals systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.
The scaling of antiferromagnetic ordering temperature of corundum-type chromia films have been investigated. Neel temperature $T_N$ was determined from the effect of perpendicular exchange-bias on the magnetization of a weakly-coupled adjacent ferromagnet. For a thick-film case, the validity of detection is confirmed by a susceptibility measurement. Detection of $T_N$ was possible down to 1-nm-thin chromia films. The scaling of ordering temperature with thickness was studied using different buffering materials, and compared with Monte-Carlo simulations. The spin-correlation length and the corresponding critical exponent were estimated, and they were consistent between experimental and simulation results. The spin-correlation length is an order of magnitude less than cubic antiferromagnets. We propose that the difference is from the change of number of exchange-coupling links in the two crystal systems.
We demonstrate stable and reversible current induced switching of large-area ($> 100;mu m^2$) antiferromagnetic domains in NiO/Pt by performing concurrent transport and magneto-optical imaging measurements in an adapted Kerr microscope. By correlating the magnetic images of the antiferromagnetic domain changes and magneto-transport signal response in these current-induced switching experiments, we disentangle magnetic and non-magnetic contributions to the transport signal. Our table-top approach establishes a robust procedure to subtract the non-magnetic contributions in the transport signal and extract the spin-Hall magnetoresistance response associated with the switching of the antiferromagnetic domains enabling one to deduce details of the antiferromagnetic switching from simple transport measurements.
Spin-orbit torque enables electrical control of the magnetic state of ferromagnets or antiferromagnets. In this work we consider the spin-orbit torque in the 2-d Van der Waals antiferromagnetic bilayer CrI$_3$, in the $n$-doped regime. In the purely antiferromagnetic state, two individually inversion-symmetry broken layers of CrI$_3$ form inversion partners, like the well-studied CuMnAs and Mn$_2$Au. However, the exchange and anisotropy energies are similar in magnitude, unlike previously studied antiferromagnets, which leads to qualitatively different behaviors in this material. Using a combination of first-principles calculations of the spin-orbit torque and an analysis of the ensuing spin dynamics, we show that the deterministic electrical switching of the Neel vector is the result of dampinglike spin-orbit torque, which is staggered on the magnetic sublattices.
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