Spintronics offers immense potential for various applications, including semiconductor devices and memory storage, due to its characteristics of nonvolatility, high speed, and low power dissipation. Spin-orbit torque (SOT)-based magnetization switching is particularly promising in this context, leveraging the Rashba effect and spin Hall effect (SHE) to control magnetization. While SOT-based switching offers efficiency, the relative contributions of damping-like torque (DLT) and field-like torque (FLT) remain a subject of ongoing research. Multiferroic heterostructures, combining ferroelectric (FE) and ferromagnetic (FM) materials, present a promising avenue for electrically controlled magnetization switching. These heterostructures enable energy conversion at room temperature and offer advantages over single-phase multiferroics like BiFeO3. This research investigates the use of multiferroic heterostructures to achieve highly efficient and energy-saving magnetization switching through precise control of SOTs using electric-field-induced strain.

Existing literature highlights the potential of SOT-based magnetization switching for energy-efficient spintronic devices. Studies have explored the mechanisms of SOT, including the Rashba effect and SHE, and the roles of DLT and FLT in various device structures. The use of multiferroic heterostructures has emerged as a promising strategy for achieving efficient electric-field control of magnetization. However, challenges remain in precisely controlling and quantifying the SOT effects. Previous research has demonstrated the feasibility of using electric field-induced strain to manipulate magnetization, but further investigation is required to optimize energy efficiency and controllability. This paper builds upon these prior studies to develop a highly energy efficient method for quantitative magnetization switching.

This study fabricated Ta/CoFeB multilayers on a PMN-PT substrate to investigate the tuning of SOTs using a perpendicular electric field. The devices were designed in various orientations (0°, 45°, 90°, 135°) to assess the angular dependence of SOT efficiency modulation. Harmonic Hall voltage measurements were performed to quantify DLT and FLT. A constant sinusoidal current was applied, and the Hall voltage was measured using a lock-in amplifier. Equations were developed to separate DLT and FLT based on their distinct dependencies on magnetic field angle and magnitude. The influence of electric fields (0-400V) on the effective fields of DLT and FLT was examined. To complement the experimental measurements, micromagnetic simulations were performed using COMSOL Multiphysics and OOMMF. A multiferroic heterostructure model was created in COMSOL to simulate strain distribution in the ferromagnetic layer under varying electric fields. This strain distribution was then input into OOMMF to simulate magnetization dynamics. Additional techniques, including Spin Transfer Torque-Ferromagnetic Resonance (ST-FMR), Magneto-optic Kerr effect (MOKE), Second harmonic spin-torque magnetometry, MFM, X-ray microdiffraction and XMCD-PEEM, were also employed to verify the magnetization switching process and strain distribution. The device fabrication process involved magnetron sputtering, optical lithography, ion milling, and evaporation/lift-off techniques.

The experimental results demonstrate that the effective field of DLT is linearly manipulable via the strain direction. Compressive strain decreases the DLT effective field, while tensile strain enhances it. The effective field of FLT, however, remains relatively constant. Micromagnetic simulations corroborate the experimental findings, showing the influence of tensile and compressive strain on different device orientations. Magnetization precession analysis showed that in-plane strain significantly assists magnetization switching, particularly at a current density of 5 x 10¹¹ A/cm². MFM images clearly illustrate the magnetization switching process under different conditions (no current, strain only, strain and current, reverse strain and current). X-ray microdiffraction results show that strain increases with applied voltage. PEEM images further confirm magnetization switching with varying substrate voltages. The electric-field-induced strain significantly reduces energy consumption, with an estimated 200 fJ per operation. The study further demonstrates the implementation of complete Boolean logic functions using the proposed architecture, including AND, OR, selector, buffer, and negation functions, based on the orientation-dependent SOT effect and electric-field-controlled strain. The device demonstrates high non-reciprocity, where magnetic states are only transferred in one direction without affecting prior inputs.

The findings demonstrate a significant advancement in energy-efficient magnetization switching. By utilizing electric-field-induced strain to precisely modulate the SOT effect, the study successfully achieved quantitative control over magnetization with significantly reduced energy consumption compared to conventional methods. The ability to implement various logic functions within a single device architecture opens avenues for highly efficient and scalable spintronic logic circuits. The combination of experimental results, micromagnetic simulations, and various characterization techniques provides strong evidence for the effectiveness of the proposed approach. The low energy consumption and reconfigurable structure of the device suggest considerable potential for future applications in low-power computing and spintronic devices.

This research presents a novel approach to energy-efficient magnetization switching using electric-field-induced strain to control SOT effects in multiferroic heterostructures. The results demonstrate precise control over magnetization switching, significant reduction in energy consumption (around 200 fJ per operation), and the capability to implement complete Boolean logic functions within a single reconfigurable device. Future work could focus on further optimization of the device design for improved performance and scalability, exploring different multiferroic materials and investigating integration with existing CMOS technology for practical applications.

The study focuses on a specific Ta/CoFeB/Pt/PMN-PT heterostructure. The performance and efficiency may vary with different materials and device geometries. The micromagnetic simulations rely on certain material parameters; variations in these parameters might affect the simulation results. The energy consumption estimation is based on a simplified model and may not fully capture all energy losses in a practical device. Further research is needed to explore the long-term reliability and stability of the device under continuous operation.