Spin-orbit Interaction Driven Phenomena in Magnetic Heterostructures

University Of Delaware, Newark DE

Investigators

Abstract

Nontechnical Abstract Recent breakthroughs in the field of spintronics, where scientists explore the spin or magnetic properties in addition to the electric properties of electrons, have created opportunities for future generations of memory and logic devices. It is found that an electrical current passing through a heavy metal such as platinum or tantalum can create, in the traverse direction, a pure spin current where electrons of opposite spin directions move in opposite directions. This pure spin current diffuses into a neighboring magnetic layer and exerts torque on spins in the magnetic layer, leading to an effective method of controlling the properties of the magnetic layer. The project aims towards acquiring a fundamental understanding of how a pure spin current traverses through materials and interfaces and interacts with spins in the magnetic layer. With novel approaches in experimental detection methods that are immune to artifacts and with interface engineering, the research team can separate and quantify various contributions arising from the bulk and interface effects. The research may also lead to new materials that provide more efficient control over nano-magnets, key ingredients in memory and logic devices. The project, leveraging on the creation of a nanofabrication facility at the University of Delaware, also aims to train undergraduate and graduate students and professionals via nanofabrication courses and certification programs. The educational activities also include outreach programs focusing on K-12 students. Technical Abstract Spin-orbit interaction (SOC) driven phenomena, such as current-induced magnetization switching and domain motion in magnetic heterostructures involving heavy metals, have attracted great attention. These phenomena arise from an intricate combination of effects including the Spin Hall Effect (SHE), interfacial Rashba SOC, and Dzyaloshinskii-Moriya Interaction (DMI), which are strongly correlated with SOC in materials and at interfaces. It is essential to understand the underlying physics responsible for these recent exciting discoveries in ferromagnetic heterostructures in order to unleash their true potential in spintronic applications. There is a lack of experimental techniques that can unravel the entanglement of torques from the SHE and Rashba effect. With designed interfaces that are nearly transparent to spin currents but significantly modify the Rashba effect and innovative 3D MOKE spin torque magnetometers that can measure torques on magnetization at arbitrary directions, the research proposes a comprehensive experimental effort to understand the rich SOC-driven phenomena in these ferromagnetic heterostructures. The project objectives are to: (1) develop 3D MOKE spin torque magnetometers capable of measuring SO torques on magnetization at an arbitrary angle, (2) quantitatively separate the SHE and Rashba SOC contributions to the SO torques, and relate them to the interface SOC, (3) characterize and optimize DMI, particularly in structures with large voltage controlled interface magnetic anisotropy, and (4) search for new material systems that possess preferred SOC-induced effects.