Tunable resistivity of individual magnetic domain walls

Role of RKKY torque on domain wall motion in synthetic antiferromagnetic nanowires with opposite spin Hall angles

We experimentally show the effect of enhanced spin-orbit and RKKY induced torques on the current-induced motion of a pair of domain walls (DWs), which are coupled antiferromagnetically in synthetic antiferromagnetic (SAF) nanowires. The torque from the spin Hall effect (SHE) rotates the Néel DWs pair into the transverse direction, which is due to the fact that heavy metals of opposite spin Hall angles are deposited at the top and the bottom ferromagnetic interfaces. The rotation of both DWs in non-collinear fashion largely perturbs the antiferromagnetic coupling, which in turn stimulates an enhanced interlayer RKKY exchange torque that improved the DW velocity. The interplay between the SHE-induced torque and the RKKY exchange torque is validated via micromagnetic simulations. In addition, the DW velocity can be further improved by increasing the RKKY exchange strength.

Influence of magnetic domain walls and magnetic field on the thermal conductivity of magnetic nanowires

We investigated the influence of magnetic domain walls and magnetic fields on the thermal conductivity of suspended magnetic nanowires. The thermal conductivity of the nanowires was obtained using steady-state Joule heating to measure the change in resistance caused by spontaneous heating. The results showed that the thermal conductivity coefficients of straight and wavy magnetic nanowires decreased with an increase in the magnetic domain wall number, implying that the scattering between magnons and domain walls hindered the heat transport process. In addition, we proved that the magnetic field considerably reduced the thermal conductivity of a magnetic nanowire. The influence of magnetic domain walls and magnetic fields on the thermal conductivity of polycrystalline magnetic nanowires can be attributed to the scattering of long-wavelength spin waves mediated by intergrain exchange coupling.

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.

Improvement of domain wall conduit properties in cobalt nanowires by global gallium irradiation

Applications based on the movement of domain walls (DWs) in magnetic nanowires (NWs) require a good DW conduit behavior, i.e. a significant difference between DW nucleation and propagation fields. In this work, we have systematically studied how this property evolves in cobalt NWs grown by focused electron beam induced deposition (FEBID) as a function of global gallium irradiation, for irradiation doses up to 1.24 × 10(17) ions cm(-2). Whereas for high doses the DW conduit is lost, below 6.42 × 10(15) ions cm(-2) the difference between the two fields increases with irradiation, becoming up to ∼9 times larger than for non-irradiated wires, due to a strong increase in the nucleation field, while the propagation field remains approximately constant. This behavior stems from two effects. The first effect is a decrease in the magnetic volume of the parasitic halo around the NW, typically present in FEBID nanostructures, leading to the disappearance of weak nucleation centers. The second effect is the formation of a 20 nm outer shell with Co crystals about twice the size of those forming the NW core, causing a net increase of the local magnetocrystalline anisotropy. The results presented here are important for the potential use of magnetic NWs grown by FEBID in DW-based devices, and might also be of interest for magnetic NWs fabricated by other techniques.

Spin-orbit-coupling-induced domain-wall resistance in diffusive ferromagnets

We investigate diffusive transport through a number of domain wall (DW) profiles of the important magnetic alloy Permalloy taking into account simultaneously noncollinearity, alloy disorder, and spin-orbit-coupling fully quantum mechanically, from first principles. In addition to observing the known effects of magnetization mistracking and anisotropic magnetoresistance, we discover a not-previously identified contribution to the resistance of a DW that comes from spin-orbit-coupling-mediated spin-flip scattering in a textured diffusive ferromagnet. This adiabatic DW resistance, which should exist in all diffusive DWs, can be observed by varying the DW width in a systematic fashion in suitably designed nanowires.