Periodic Reporting for period 1 - SpinDy (Dynamical control of Spintronic devices through solid-state gating)
Berichtszeitraum: 2023-09-01 bis 2025-08-31
The increasing reliance on digital technologies is driving up data storage and processing demands, leading to a sharp rise in energy consumption. As data becomes one of the most valuable assets of modern society, managing this energy use is crucial for sustainable development. Addressing this challenge requires a paradigm shift in the microelectronics industry, grounded in novel and more energy-efficient technologies. In this context, spintronics—which exploits the spin degree of freedom of charge carriers in electronic devices—offers promising solutions for next-generation computing. Spintronics is particularly well-suited for improving the energy efficiency of magnetic data storage and logic, as it enables the electrical switching and modulation of magnetism without the need for external magnetic fields.
Recent breakthroughs have further revealed the potential to use light metals and rare-earth-free magnetic materials in spintronic devices. This development aligns with the urgent need to transition toward cleaner technologies that are more sustainable and environmentally friendly.
In this context, the SpinDy project addresses both fundamental and technological challenges in spintronics by exploring novel strategies for developing proof-of-concept devices that enable highly efficient data manipulation. The project goal is to create spintronic systems that can be dynamically switched between two distinct operational states: one optimized for low-power reading and writing, and another designed for robust, non-volatile information storage. This functionality is made possible by tuning the energy barrier for magnetic switching through voltage-driven ion migration across a solid-state gate. Applying a gate voltage enables the reversible modification of material composition within the device, which in turn alters its spin transport properties and operational mode. This approach allows for energy-efficient operation without sacrificing long-term data retention, paving the way for future computing technologies that are both high-performing and sustainable.
Recent breakthroughs have further revealed the potential to use light metals and rare-earth-free magnetic materials in spintronic devices. This development aligns with the urgent need to transition toward cleaner technologies that are more sustainable and environmentally friendly.
In this context, the SpinDy project addresses both fundamental and technological challenges in spintronics by exploring novel strategies for developing proof-of-concept devices that enable highly efficient data manipulation. The project goal is to create spintronic systems that can be dynamically switched between two distinct operational states: one optimized for low-power reading and writing, and another designed for robust, non-volatile information storage. This functionality is made possible by tuning the energy barrier for magnetic switching through voltage-driven ion migration across a solid-state gate. Applying a gate voltage enables the reversible modification of material composition within the device, which in turn alters its spin transport properties and operational mode. This approach allows for energy-efficient operation without sacrificing long-term data retention, paving the way for future computing technologies that are both high-performing and sustainable.
The Spindy project implements gate-tunable devices based on two distinct concepts. The first approach focuses on controlling spin-orbit torque (SOT) efficiency at the interface between a metal and a ferromagnet. This is achieved by tuning orbital currents in light transition metals through controlled oxidation and reduction processes. To investigate this, we conducted a detailed characterization of spin and orbital torques in bilayers composed of copper (Cu) and ferromagnets such as cobalt (Co) and permalloy (Py). Our results revealed that both the magnitude and sign of the damping-like torque strongly depend on the oxidation state of Cu and the specific ferromagnet used. Building on these findings, we developed solid-state gated devices in which Cu can be reversibly oxidized by driving oxygen ions across a gadolinium oxide gate. Using these devices, we demonstrated that the amplitude of the damping-like torque can be modulated by the applied gate voltage. The second approach involves tailoring the magnetic properties of the rare-earth-free metallic ferrimagnet Mn₄N. After optimizing the growth of epitaxial Mn₄N thin films with perpendicular magnetic anisotropy, bulk-like magnetic saturation and good magnetotransport properties, we showed that the coercivity of these films can be tuned by reversibly modifying their nitrogen content through voltage-driven nitrogen migration. This is accomplished in solid-state gated devices by interfacing Mn₄N with nitrogen-affine metals such as vanadium (V) or tantalum (Ta). Our experiments demonstrate that Mn₄N can be switched between a low-coercivity state, where magnetization can be electrically reversed using low current, and a high-coercivity state, suitable for robust magnetic information storage. In such devices, when the magnetization vector is set with a low field in the low coercivity state, its orientation retained after gating to the high coercivity state. This represents a proof-of-principle energy efficient tunable device. We also demonstrate that the magnetization of Mn₄N can be electrically switched using an applied current. However, the switching is only partial, as the current required to reverse the magnetization throughout the entire film thickness generates excessive heat, risking device failure. Notably, the switching efficiency improves after gating, highlighting the potential of these devices as a promising platform for fully electrical reading and writing of magnetic information.
The results of the SpinDy project represent a significant advancement over the current state-of-the-art in spintronic technology across several dimensions. From a materials perspective, we demonstrated that large spin-orbit torques can be generated in light metals such as copper (Cu), eliminating the need for heavy metals like platinum (Pt), which are both rare and costly. We also achieved notable progress in the fabrication of rare-earth-free ferrimagnetic films with perpendicular magnetic anisotropy—suitable for use as active layers in magnetic memory applications. On the fundamental physics side, we explored novel mechanisms for generating spin-orbit torques and provided new insights into the origin of orbital momentum accumulation in Cu/ferromagnet bilayers. Our findings suggest that the damping-like torque component stems from the orbital Hall effect in CuOx, while the field-like component is primarily due to interface effects. Technologically, we developed proof-of-concept devices that validate the feasibility of dynamically tunable functionalities. However, we identified a key limitation: the inherent slowness of voltage-driven ion migration. To address this, future research should focus on accelerating the response time—potentially through hydrogen-based magnetoionic approaches.