Bart Sorée

We investigate the differential voltage generation originating from the direct magnetoelectric effect in nanoscale composite devices during magnetization rotation from the magnetic ground state to an out-of-plane configuration. The devices consist of a magnetostrictive ferromagnetic layer mechanically coupled to a piezoelectric layer. Using finite-element modeling in comsol Multiphysics, we systematically analyze strain transfer mechanisms and the resulting open-circuit voltage generation as a function of material and geometric parameters. At nanoscale dimensions, two distinct strain transfer regimes emerge, with the dominant mechanism governed by both device aspect ratio and magnetic state. Surface clamping effects are found to diminish with decreasing pillar diameter and increasing aspect ratio, while strain transfer to the piezoelectric layer is enhanced by stiffer electrodes or additional clamping layers. Furthermore, magnetostrictive materials with large magnetoelastic coupling and high Poisson ratio substantially increase the voltage output at small dimensions. These results provide design guidelines for material selection and dimensional scaling of magnetoelectric pillars. Output voltages exceeding 200 mV are predicted for scaled devices, highlighting their potential for integration in microelectronic applications.

We present a flexible modeling framework for flopping-mode spin qubits that captures the spatial structure of the double-well confinement and magnetic-field-gradient profile going beyond conventional low-energy descriptions. By using this approach, we simulate electric dipole spin resonance-based single-qubit control and evaluate the frequency and spectral purity of the Rabi oscillations across different parameter regimes. Our analysis reveals a fundamental trade-off between fast electrical driving and clean single-mode Rabi oscillations and demonstrates that the standard two-site low-energy approximation can overestimate the Rabi frequency by up to ∼20% in certain parameter regimes. We also investigate two-qubit control by considering two capacitively coupled flopping-mode qubits and derive the corresponding exchange interaction with an appropriately restricted configuration interaction treatment. Our approach reveals the interplay between the spatial profile of the double-well confinement, magnetic field gradient, and Coulomb interaction, which together govern the effective exchange coupling strength. Our spatially resolved modeling framework enables efficient exploration of double-well confinement parameters and magnetic field gradient profiles, enabling a transparent mapping from spatial device properties to flopping-mode qubit parameters and quality metrics.

Chirally coupled magnetic tunnel junctions (MTJs) have been proposed as a route toward compact spin logic architectures. Micromagnetic simulations indeed show that chiral coupling between adjacent MTJs with perpendicular magnetic anisotropy (PMA) can be achieved through an in‐plane (IP) interconnection mediated by the Dzyaloshinskii–Moriya interaction, eliminating the need for current‐driven domain‐wall motion. Nevertheless, experimental implementation of this concept requires precise manipulation of PMA to define IP interconnections between MTJs, as well as independent control of DMI to ensure reliable coupling. Here, we introduce a hybrid free layer (HFL) stack comprising an Ir/Co bottom layer and a CoFeB/MgO top layer providing PMA. We show that ultrathin Pt insertion layers at the Ir/Co interface provide an effective means to tune the DMI without affecting PMA, enabling independent control of both properties. Finally, we develop an ion beam etching (IBE) process on a 300‐mm platform that selectively suppresses the CoFeB/MgO contribution to PMA, thereby converting the stack to IP magnetization. This approach enables the manipulation of the PMA of the interconnecting free layer during MTJ patterning, providing a scalable pathway for the fabrication of chirally coupled MTJs.

We present micromagnetic simulations and experiments on voltage-assisted field switching in perpendicular magnetic tunnel junctions (MTJs) with a synthetic antiferromagnetic (SAF) free layer, where the magnetic state of one sublayer is detected via tunneling magnetoresistance (TMR). Simulations reveal that local modulation of perpendicular magnetic anisotropy in one SAF sublayer leads to distinct switching characteristics. The switching field varies linearly with the anisotropy field, indicating voltage-controlled magnetic anisotropy (VCMA)-dominated dynamics similar to single free-layer devices. We then experimentally study the magnetic switching field of MTJ devices with SAF free layers under applied gate voltage. By varying the MgO tunnel barrier thickness to systematically modulate the resistance-area (RA) product, we enable quantitative separation of spin-transfer torque (STT), VCMA, and Joule heating contributions. Our findings indicate that VCMA dominates in devices with a high-RA product, while low-RA devices exhibit nonlinear switching behavior due to enhanced contributions from STT and Joule heating. Furthermore, the effective fields derived from STT, VCMA, and Joule heating contributions under various gate voltages show minimal dependence on device critical dimensions, indicating favorable scaling behavior. This work presents a unified framework analyzing the roles of STT, VCMA, and Joule heating in SAF-based voltage-gated spin–orbit torque (SOT) magnetic random-access memory (MRAM), offering key insights for the optimization of performance, energy efficiency, and scalability in SOT-MRAM technologies.

This study investigates the direct magnetoelectric effect in thin film composites comprising a 550 nm thick poly(vinylidene fluoride‐trifluoroethylene) (PVDF‐TrFE) layer spin‐coated onto a 500 µm thick Ni foil substrate. Direct measurements of charge accumulation on dot capacitors with Au top electrodes, induced by the rotation of Ni magnetization from in‐plane to out‐of‐plane orientation by an applied magnetic field, reveal pronounced magnetoelectric coupling. Polarization differences between in‐plane and out‐of‐plane magnetization states of up to (13.8 ± 0.8) × 10⁻⁴ µC cm⁻² are derived from charge measurements. This corresponds to a maximum open circuit voltage difference of up to 75 ± 6 mV and a magnetoelectric coupling coefficient with respect to magnetization changes of 310 ± 27 mVA⁻¹. Finite element simulations using COMSOL Multiphysics corroborate experimental findings, indicating near‐independence of generated polarizations and open circuit voltages when lateral capacitor dimensions are reduced into the nanometer range. Simulations of nanoscale pillar devices on rigid substrates, employing materials with optimized piezoelectric and magnetostrictive parameters, predict the potential for generating large open circuit voltage differences exceeding 2 V, highlighting the prospects of such devices for spintronic applications.