Multiferroic tunnel junctions (MFTJs) with Hf_0.5Zr_0.5O₂ barriers are reported to show both tunneling magnetoresistance effect (TMR) and tunneling electroresistance effect (TER), displaying four resistance states by magnetic and electric field switching. Here we show that, under electric field cycling of large enough magnitude, the TER can reach values as large as 10⁶%. Moreover, concomitant with this TER enhancement, the devices develop electrical control of spin polarization, with sign reversal of the TMR effect. Currently, this intermediate state exists for a limited number of cycles and understanding the origin of these phenomena is key to improve its stability. The experiments presented here point to the magneto-ionic effect as the origin of the large TER and strong magneto-electric coupling, showing that ferroelectric polarization switching of the tunnel barrier is not the main contribution.

The domain wall response under constant external magnetic fields reveals a complex behavior where sample disorder plays a key role. Furthermore, the response to alternating magnetic fields has only been explored in limited cases and analyzed in terms of the constant field solution. Here we unveil phenomena in the evolution of magnetic domain walls under the application of alternating magnetic fields within the creep regime, well beyond a small fluctuation limit of the domain wall position. Magnetic field pulses were applied in ultrathin ferromagnetic films with perpendicular anisotropy, and the resulting domain wall evolution was characterized by polar magneto-optical Kerr effect microscopy. Whereas the dc characterization is well predicted by the elastic interface model, striking unexpected features are observed under the application of alternating square pulses: Magneto-optical images show that after a characteristic number of cycles, domain walls evolve toward strongly distorted shapes concomitantly with a modification of domain area. The morphology of domain walls is characterized with a roughness exponent when possible and contrasted with alternative observables which are more suitable for the characterization of this transient evolution. The final stationary convergence as well as the underlying physics is discussed.

Electronic conduction along individual domain walls (DWs) is reported in BiFeO₃ (BFO) and other nominally insulating ferroelectrics. DWs in these materials separate regions of differently oriented electrical polarization (domains) and are just a few atoms wide, providing self‐assembled nanometric conduction paths. Herein, it is shown that electronic transport is possible also from wall‐to‐wall through the dense network of as‐grown DWs in BFO thin films. Electric field cycling at different points of the network, performed locally by conducting atomic force microscopy (cAFM), induces resistive switching selectively at the DWs, both for vertical (single wall) and lateral (wall‐to‐wall) conduction. These findings are the first step toward investigating DWs as memristive networks for information processing and in-materio computing.

Designing magnetic materials for potential applications based on domain wall motion requires the knowledge of the relationship between physical properties and phenomenological parameters characterizing domain wall dynamics. We address in this work the study of magnetic-field-driven domain wall motion within the creep regime on a prototypical metallic Pt/Co/Pt stack with perpendicular magnetic anisotropy. By controlling the deposition characteristics, different magnetic properties are achieved, giving rise to different creep parameters. Those phenomenological parameters are found to collapse in a single linear dependence for all samples based on the same material. Moreover, using data in the literature, we show that the same behavior is observed in Au/Co/Au and Tb/Fe based samples. We therefore obtain a pair of global parameters that fully characterize the family of domain wall velocity-field curves within the creep regime for each group of samples, which can be used as input for the optimization of materials.

We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core-shell ${\mathrm{Fe}}_3{\mathrm{O}}_4$/${\mathrm{Co}}_{1-x}{\mathrm{Zn}}_x{\mathrm{Fe}}_2{\mathrm{O}}_4$ nanoparticles ($0\le x\le 1$). Adjusting the magnetic anisotropy through the content of ${\mathrm{Co}}^{2+}$ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft-hard and hard-soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response.