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Controlling the magnetic anisotropy in magnetic oxides is critical for the development of oxide spintronics. Here we report on the finding of an emergent interfacial magnetism, with unique perpendicular magnetic anisotropy (PMA), at the interface of a half-doped manganite ${\mathrm{La}}_{1/2}{\mathrm{Sr}}_{1/2}\mathrm{Mn}{\mathrm{O}}_{3}$ film on $\mathrm{LaAl}{\mathrm{O}}_{3}$ substrate, through combined electron spin resonance measurements and density functional theory calculations. The interfacial magnetism can be explained by the $3{d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital-mediated ferromagnetic exchange interaction between Mn ions near the interface, which is enhanced by the compressive strain from the substrate. Our results provide a useful PMA system for possible spintronic applications, as well as atomistic-level insight to the magnetic anisotropy in strained manganite oxide interfaces.

Understanding the transport of spin current in antiferromagnetic materials is indispensable to develop antiferromagnetic spintronic devices. In this work, we study the spin current transmission through an antiferromagnetic IrMn insertion layer in a W/IrMn($t$)/CoFeB structure by measuring the spin Hall magnetoresistance (SMR) and spin-orbit torque (SOT). The temperature dependences of SMR and SOT effective fields indicate that the spin current transmission reaches its maximum at the N\'eel temperature of IrMn. The enhancement is ascribed to the increase in the interfacial spin mixing conductance, which is related to the maximum magnetic susceptibility of the IrMn layer at the N\'eel temperature. The spin transmission decreases monotonically as a function of the IrMn thickness, which is different from the case with an insulating antiferromagnetic NiO insertion layer in previous works. In addition, we found that the spin transmission through an antiferromagnetic IrMn layer is independent of the exchange bias orientation. Our results suggest that the spin current transmission through the IrMn layer (from W layer to CoFeB layer) is mainly mediated by spin-polarized electrons rather than magnons, which is likely due to the absence of the effective excitation of magnons in the IrMn layer by the spin-polarized current.

Spin current generated in a ferromagnetic metal (FM) can be divided into two types. While one is magnetization dependent and induced by the well-known anomalous Hall effect, the other is a magnetization-independent spin Hall effect which is similar to that in a paramagnetic heavy metal (HM). Here, we study the magnetization-independent spin Hall current in YIG/FM (NiFe and CoFeB) via spin-torque ferromagnetic resonance (ST-FMR) technique. Our experiments reveal the existence of a magnetization-independent spin current. Although there is a strong exchange interaction in FM, the spin current does not dephase as quickly as expected. Furthermore, we estimate the spin-torque efficiency $\ensuremath{\xi}$ of NiFe was 0.009, which is about $25%$ of the spin-torque efficiency of Pt. These results indicate that the spin Hall effect of FM should also be taken into account when investigating FM/HM heterostructures, and furthermore this effect can also benefit from the development of spin-orbit torque devices.

To enable functional skyrmion based spintronic devices, the controllable generation and manipulation of skyrmions is essential. While the generation of skyrmions by using a magnetic geometrical constriction has already been demonstrated, this approach is difficult to combine with a subsequent controlled manipulation of skyrmions. The high efficiency of skyrmion generation from magnetic constrictions limits the useful current density, resulting in stochastic skyrmion motion, which may obscure topological phenomena such as the skyrmion Hall effect. In order to address this issue, we designed a nonmagnetic conducting Ti/Au point contact in devices made of Ta/CoFeB/TaOx trilayer films. By applying high voltage pulses, we experimentally demonstrated that skyrmions can be dynamically generated. Moreover, the accompanied spin topology dependent skyrmion dynamics, the skyrmion Hall effect is also experimentally observed in the same devices. The creation process has been numerically reproduced through micromagnetic simulations in which the important role of skyrmion-antiskyrmion pair generation is identified. The motion and Hall effect of the skyrmions, immediately after their creation is described using a modified Thiele equation after taking into account the contribution from spatially inhomogeneous spin-orbit torques and the Magnus force. The simultaneous generation and manipulation of skyrmions using a nonmagnetic point contact could provide a useful pathway for designing novel skyrmion based devices., All comments are welcome

We use temperature-dependent Hall measurements to identify contributions of spin Hall, magnetic proximity, and sublattice effects to the anomalous Hall signal in heavy metal/ferrimagnetic insulator heterostructures with perpendicular magnetic anisotropy. This approach enables detection of both the magnetic proximity effect onset temperature and the magnetization compensation temperature and provides essential information regarding the interfacial exchange coupling. Onset of a magnetic proximity effect yields a local extremum in the temperature-dependent anomalous Hall signal, which occurs at higher temperature as magnetic insulator thickness increases. This magnetic proximity effect onset occurs at much higher temperature in Pt than W. The magnetization compensation point is identified by a sharp anomalous Hall sign change and divergent coercive field. We directly probe the magnetic proximity effect using x-ray magnetic circular dichroism and polarized neutron reflectometry, which reveal an antiferromagnetic coupling between W and the magnetic insulator. Finally, we summarize the exchange-coupling configurations and the anomalous Hall-effect sign of the magnetized heavy metal in various heavy metal/magnetic insulator heterostructures.

Magnetic skyrmions in multilayers are particularly appealing as next generation memory devices due to their topological compact size, the robustness against external perturbations, the capability of electrical driving and detection, and the compatibility with the existing spintronic technologies. To date, N\'eel-type skyrmions at room temperature (RT) have been studied mostly in multilayers with easy-axis magnetic anisotropy. Here, we systematically broadened the evolution of magnetic skyrmions with sub-50-nm size in a series of Pt/Co/Ta multilayers where the magnetic anisotropy is tuned continuously from easy axis to easy plane by increasing the ferromagnetic Co layer thickness. The existence of nontrivial skyrmions is identified via the combination of in situ Lorentz transmission electron microscopy (L-TEM) and Hall transport measurements. A high density of magnetic skyrmions over a wide temperature range is observed in the multilayers with easy-plane anisotropy, which will stimulate further exploration for new materials and accelerate the development of skyrmion-based spintronic devices.

We theoretically study equilibrium and dynamic properties of nanosized magnetic skyrmions in thin magnetic films with broken inversion symmetry, where electric field couples to magnetization via spin-orbit coupling. Based on a symmetry-based phenomenology and micromagnetic simulations we show that this electric-field coupling, via renormalizing the micromagnetic energy, modifies the equilibrium properties of the skyrmion. This change, in turn, results in a significant alteration of the current-induced skyrmion motion. Particularly, speed and direction of the skyrmion can be manipulated by designing a desired energy landscape electrically, which we describe within Thiele's analytical model and demonstrate in micromagnetic simulations including electric-field-controlled magnetic anisotropy. We additionally use this electric-field control to construct gates for controlling skyrmion motion exhibiting a transistor-like and multiplexer-like function. The proposed electric-field effect can thus provide a low energy electrical knob to extend the reach of information processing with skyrmions., Comment: 9 pages, 7 figures

The influence of spin-Hall-effect spin torque (SHE-ST) induced by in-plane charge current was studied in microscale Ta/Co${}_{20}$Fe${}_{60}$B${}_{20}$/TaO${}_{x}$ films with perpendicular magnetization. Simultaneous electrical transport and polar magneto-optical Kerr effect (MOKE) imaging experiments were used to investigate the switching dynamics. A rich set of switching behaviors was observed, which can be well understood by analyzing a switching-phase diagram and polar MOKE images, considering the competition between SHE-ST and the externally applied magnetic field. Furthermore, we found that domain walls with a particular chirality were dominant in our devices, which suggests the presence of the Dzyaloshinskii-Moriya interaction in the present material system.