We have studied the domain-wall dynamics in Ta-CoFeB-MgO ultra-thin films with perpendicular magnetic anisotropy for various Co and Fe concentrations in both the amorphous and crystalline states. We observe three motion regimes with increasing magnetic field, which are consistent with a low fields creep, transitory depinning, and high fields Walker wall motion. The depinning fields are found to be as low as 2 mT, which is significantly lower than the values typically observed in 3d ferromagnetic metal films with perpendicular magnetic anisotropy. This work highlights a path toward advanced spintronics devices based on weak random pinning in perpendicular CoFeB films.

We report on current-induced domain wall motion in $\mathrm{Ta}/\mathrm{C}{\mathrm{o}}_{20}\mathrm{F}{\mathrm{e}}_{60}{\mathrm{B}}_{20}/\mathrm{MgO}$ nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient $D=+0.06\mathrm{mJ}/{\mathrm{m}}^2$. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta buffer layer during annealing, which was observed by chemical depth profiling measurements. The experimental results are compared to one-dimensional model simulations including the effects of pinning. This modeling allows us to reproduce the experimental outcomes and reliably extract a spin-Hall angle ${\theta }_{\mathrm{SH}}=\text{–}0.11$ for Ta in the nanowires, showing the importance of an analysis that goes beyond the model for perfect nanowires.

The possibility of tuning the Dzyaloshinskii-Moriya interaction (DMI) by electric (E)-field gating in ultrathin magnetic materials has opened up new perspectives in terms of controlling the stabilization of chiral spin structures. The most recent efforts have used voltage-induced charge redistribution at the interface between a metal and an oxide to modulate the DMI. This approach is attractive for active devices but tends to be volatile, making it energy-demanding, and it is limited by Coulomb screening in the metal. Here we demonstrate nonvolatile E-field manipulation of the DMI by ionic-liquid gating of $\mathrm{Pt}/\mathrm{Co}/{\mathrm{Hf}\mathrm{O}}_2$ ultrathin films. The E-field effect on the DMI scales with the E-field exposure time, and we propose that it is linked to the migration of oxygen species from the ${\mathrm{Hf}\mathrm{O}}_2$ layer into the $\mathrm{Co}$ and $\mathrm{Pt}$ layers and subsequent anchoring. This effect permanently changes the properties of the material, showing that E fields can be used not only for local gating in devices but also as a highly scalable materials design tool for postgrowth tuning of the DMI.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) plays a crucial role in chiral domain wall (DW) motion, favoring fast DW velocities. We explore the effect of interface disorder on DMI and DW dynamics in perpendicular magnetized Ta/CoFeB/MgO thin films. Light ${\mathrm{He}}^{+}$ irradiation has been used to gently engineer interface intermixing on a scale of 0.1 nm. We demonstrate that a slight modification of the Ta/CoFeB interface leads to an increase of the DMI value accompanied by an enhancement of DW velocity in the flow regime. Using micromagnetic simulations based on granular structures, we show that the enhancement of DW velocity is mainly related to an increase in the distribution of magnetic parameters related to the interface. We further infer that the DMI modulation is related to the asymmetric disorder induced by irradiation leading to alloying with the Ta buffer layer. Understanding the role of disorder is therefore crucial for the design of future devices where post-growth interface alloying can be used to finely tune the DMI.

Resistive switching memory (RRAM) based on the redox-induced conductivity change in some metal oxides attracts considerable interest as a new technology for next-generation nonvolatile electronic storage. Although resistance-switching phenomena in several transition metal oxides have been known from decades, the details of the switching mechanisms and the nature of the different resistive states are still largely debated. For nonvolatile memory applications, the scaling potential of RRAMs is the most relevant issue, and understanding the scaling capability of RRAM devices requires a sound interpretation of resistance-switching operation and reliability aspects. This work addresses the scaling dependence of RRAM switching parameters. The dependence on the electrode area and on the size of the conductive filament (CF) responsible for low-resistance memory state is investigated. The RRAM conduction modes depending on CF size are discussed based on temperature dependent resistance analysis. Reset characteristics in different resistance states are explained by a Joule heating model for CF oxidation.