The project

This project aims to determine the role of interfacial intermixing in the spin-orbit torque across QM/FM and QM/ferrimagnetic oxide (FO) heterostructures with both experimental and theoretical perspectives. In this new class of artificial materials, unique proximity effects and intermixing that are absent in conventional materials lead to novel physical phenomena. The investigated heterostructures are 1) charge-to-spin converters: when a current passes in the film plane a spin current perpendicular to the plane is generated. This spin current can switch the magnetization of the adjacent ferro-/ferrimagnetic layer or drive its magnetization into continuous precession.; 2) spin-to-charge converters: when a resonant HF signal is applied a spin current is pumped perpendicular to the plane and generates a charge current in the film plane. These two principles allow for the realization of memories and logic and microwave generators or current/field sensors. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Realizing efficient spin-orbit-based switching requires the harnessing of both new materials and novel physics to obtain high charge-to-spin conversion efficiencies, thus making the choice of the materials and interface engineering crucial. 

The need for fast, energy-efficient magnetization manipulation in big data has driven the development of Spin-Orbit Torque (SOT). SOT, which originates from spin-orbit coupling effects (like the Spin Hall, Anomalous Hall, and Rashba effects), offers superior efficiency and speed compared to the classic Spin-Transfer Torque (STT).

SOT is a crucial technique for next-generation spintronics devices, including SOT-MRAM, spin nano-oscillators, and spin logic. Typical SOT devices consist of two functional materials: a spin source (with strong spin-orbit coupling for charge-spin interconversion) and a magnetic material (for information processing and archiving).

Electrical-current-induced magnetization switching is key to energy-efficient spintronics. While SOT-based spintronics provides non-volatility, speed, and low power consumption by using pure spin currents, challenges remain for practical application.

Key Developments in SOT Research:

1.  Characterization and Manipulation: Developing reliable electrical measurement methods to understand SOT's physical properties in heavy-metal/ferromagnet heterostructures, differentiating between interfacial and bulk contributions.

2.  Emerging Quantum Materials: Utilizing materials like topological insulators (TIs), 2D materials, and non-collinear antiferromagnets for efficient spin and charge conversion, leading to unique, often gate-tunable, spin-dependent phenomena.

3.  Interface Effects: Studying spin and charge conversion via Rashba States and Edelstein/inverse Edelstein Effects at various interfaces.

4.  Next-Generation Devices: SOT, especially utilizing the Spin Hall and Rashba effects, is a promising alternative to current high-current-density magnetic switching. Developing SOT nanodevices using 2D topological and van der Waals (vdW) materials offers improved efficiency and reduced heating compared to conventional 3D materials.