CAREER: Self-generated spin-orbit torques driven by universal Hall effects

Non-technical Abstract:

Manipulation of materials properties at the nanoscale offers transformative potential for energy-efficient information processing and storage. For example, manipulation of a property known as spin-orbit torque allows one to change magnetic properties using an electrical current. This process can be ultrafast and energy efficient.

Developing new methods and materials allowing such manipulation of magnetic properties is essential to advancing next-generation spintronic devices. This project seeks to establish precise causal links between ferromagnetic material properties and universal torque behavior. The outcomes are expected to have a significant positive impact on the knowledge and understanding of novel magnetic materials.

This project engages students across educational stages, modernizes an advanced lab course, and provides hands-on physics learning to underrepresented middle and high school students. By providing participants with essential skills for developing next-generation semiconductor technologies, this project seeks to strengthen the domestic talent pool and enhance the economic competitiveness of the U.S.

Technical Abstract:

Spin-transfer torque and spin-orbit torques have enabled control of the magnetization vector in magnetic materials using electric fields or currents. Recent breakthroughs in self-generated planar and anomalous Hall torques have expanded the range of materials capable of generating giant spin-orbit torques. These torques are self-generated as they act on the same ferromagnet where the spin current is produced.

Alongside spin Hall torque, planar Hall and anomalous Hall torques form a triad of universal Hall torques, which are expected to arise in all magnetic conductors. However, the fundamental mechanisms driving these torques remain poorly understood. This project aims to achieve a deeper understanding of the interplay between charge and spin transport in the triad of Hall effects and how it induces self-torque on the magnetization of magnetic materials.

Spin-orbit torque characterization within this project entails spin-torque ferromagnetic resonance measurements in nanowire structures fabricated by magnetron sputtering and e-beam lithography. This project seeks to establish precise causal links between ferromagnetic material properties, in particular electronic band structure and material interfaces, and universal Hall torque behavior to uncover the microscopic mechanisms underlying these torques.

The anticipated results are expected to advance the fundamental understanding of coupled charge-and-spin transport and coherent spin manipulation in ferromagnetic conductors. This knowledge has the potential to transform the design and development of next-generation spintronic devices.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.