Tunable chiral spin texture in magnetic domain-walls

Magnetic domain-walls (DWs) with a preferred chirality exhibit very efficient current-driven motion. Since structural inversion asymmetry (SIA) is required for their stability, the observation of chiral domain walls in highly symmetric Pt/Co/Pt is intriguing. Here, we tune the layer asymmetry in this system and observe, by current-assisted DW depinning experiments, a small chiral field which sensitively changes. Moreover, we convincingly link the observed efficiency of DW motion to the DW texture, using DW resistance as a direct probe for the internal orientation of the DW under the influence of in-plane fields. The very delicate effect of capping layer thickness on the chiral field allows for its accurate control, which is important in designing novel materials for optimal spin-orbit-torque-driven DW motion.Comment: 12 pages, 5 figure

Precession-torque-driven domain-wall motion in out-of-plane materials

Domain-wall (DW) motion in magnetic nanostrips is intensively studied, in particular because of the possible applications in data storage. In this work, we will investigate a novel method of DW motion using magnetic field pulses, with the precession torque as the driving mechanism. We use a one dimensional (1D) model to show that it is possible to drive DWs in out-of-plane materials using the precession torque, and we identify the key parameters that influence this motion. Because the DW moves back to its initial position at the end of the field pulse, thereby severely complicating direct detection of the DW motion, depinning experiments are used to indirectly observe the effect of the precession torque. The 1D model is extended to include an energy landscape in order to predict the influence of the precession torque in the depinning experiments. Although preliminary experiments did not yet show an effect of the precession torque, our calculations indicate that depinning experiments can be used to demonstrate this novel method of DW motion in out-of-plane materials, which even allows for coherent motion of multiple domains when the Dzyaloshinskii-Moriya interaction is taken into account

Large magnetoresistance using hybrid spin filter devices

A magnetic "spin filter" tunnel barrier, sandwiched between a non-magnetic metal and a magnetic metal, is used to create a new magnetoresistive tunnel device, somewhat analogous to an optical polarizer-analyzer configuration. The resistance of these trilayer structures depends on the relative magnetization orientation of the spin filter and the ferromagnetic electrode. The spin filtering in this configuration yields a previously unobserved magnetoresistance effect, exceeding 100%.Comment: 3.5 pages, 3 figures, submitted to Appl. Phys. Let

Correlation between magnetism and spin-dependent transport in CoFeB alloys

We report a correlation between the spin polarization of the tunneling electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a correlation is surprising since the TSP involves s-like electrons close to the Fermi level (EF), while the magnetic moment mainly arises due to all d-electrons below EF. We show that probing the s and d-bands individually provides clear and crucial evidence for such a correlation to exist through s-d hybridization, and demonstrate the tuneability of the electronic and magnetic properties of CoFeB alloys.Comment: Accepted for publication in Physical Review Letters. Letter (4 pages) and Supplementary material (4 pages

Large interfacial spin-orbit torques in layered antiferromagnetic insulator NiPS3/ferromagnet bilayers

Finding efficient ways of manipulating magnetic bits is one of the core goals in spintronic research. Electrically-generated spin-orbit torques (SOTs) are good candidates for this and the search for materials capable of generating highly-efficient SOTs has gained a lot of traction in the recent years. While antiferromagnet/ferromagnet bilayer structures have been employed extensively for passive applications, e.g. by using exchange bias fields, their active properties are not yet widely employed. Here we show the presence of large interfacial SOTs in bilayer of a ferromagnet and the two-dimensional layered antiferromagnetic insulator NiPS$_3$. We observe a large in-plane damping-like interfacial torque, showing a torque conductivity of $\sigma_\mathrm{DL} \approx 1 \times 10^{5} \mathrm{(\frac{\hbar}{2e}) /(\Omega m)}$ even at room temperature, comparable to the best devices reported in the literature for standard heavy-metal-based and topological insulators-based devices. Additionally, our devices also show an out-of-plane field-like torque arising from the NiPS$_3$/ferromagnet interface, further indicating the presence of an interfacial spin-orbit coupling in our structures. Temperature-dependent measurements reveal an increase of the SOTs with a decreasing temperature below the N\'eel temperature of NiPS$_3$ ($T_N \approx 170 \mathrm{K}$), pointing to a possible effect of the magnetic ordering on our measured SOTs. Our findings show the potential of antiferromagnetic insulators and two-dimensional materials for future spintronic applications.Comment: 19 pages, 3 figures, 1 table. Changed units of the torque normalized by the electric field from $\mathrm{\mu m \, T/V}$ to $\mathrm{nm \, T/V}

Spin motive forces due to magnetic vortices and domain walls

We study spin motive forces, i.e, spin-dependent forces, and voltages induced by time-dependent magnetization textures, for moving magnetic vortices and domain walls. First, we consider the voltage generated by a one-dimensional field-driven domain wall. Next, we perform detailed calculations on field-driven vortex domain walls. We find that the results for the voltage as a function of magnetic field differ between the one-dimensional and vortex domain wall. For the experimentally relevant case of a vortex domain wall, the dependence of voltage on field around Walker breakdown depends qualitatively on the ratio of the so-called $\beta$-parameter to the Gilbert damping constant, and thus provides a way to determine this ratio experimentally. We also consider vortices on a magnetic disk in the presence of an AC magnetic field. In this case, the phase difference between field and voltage on the edge is determined by the $\beta$ parameter, providing another experimental method to determine this quantity.Comment: 8 pages, 9 figures, submitted to PR

Direct observation of the barrier asymmetry in magnetic tunnel junctions

A photoconductance method has been used to study directly the barrier asymmetry in TaOx magnetic tunnel junctions. Due to optical electron-hole pair generation in the barrier itself and subsequent transport in the elec. field, the sign and magnitude of the barrier asymmetry can be detd. quite accurately. The reliability of the technique is demonstrated by the independence on the direction of illumination. The oxidn. time where the asymmetry becomes zero is found to coincide with a max. in the magnetoresistance ratio. This is argued to be due to the complete oxidn. of the barrier material, resulting in a sym. tunnel barrier. [on SciFinder (R)