CAREER: Low-Loss Spintronic Devices with Vertically Engineered Magnets

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In personal computers and data centers, information is often stored in magnetic films where the two digital states (“0” and “1”) are represented by opposite magnetization directions. Switching the magnetization with low loss (minimal wasted energy) is key to developing energy-efficient digital memory devices. In recent years, an effect called “spin-orbit torque” has been envisioned as a promising way to switch next-generation magnetic memories. However, the outstanding problem is that stronger spin-orbit torques require extremely thin, lossy magnetic films, in which switching involves a large amount of wasted energy. The proposed research will resolve this longstanding problem by developing a new family of magnetic films with tailored chemical composition profiles, which simultaneously enable strong spin-orbit torques and low loss. A successful outcome of this research will improve the energy efficiency of spin-orbit-torque magnetic memories by more than a hundredfold. In addition, research will advance the basic understanding of how spin-orbit torques and losses arise in magnetic materials, with broader applications in not only digital memories but also brain-inspired and quantum computing technologies. Moreover, it is proposed to develop a hands-on in-class activity for elementary school students to build audio speakers with inexpensive materials. This activity will help students develop a long-lasting appreciation for how the physical concepts of electricity, magnetism, and sound apply to everyday technologies. Spin-orbit torque (SOT) devices for memory and computing applications are typically bilayers, consisting of a magnetic film interfaced with a spin-orbit material. The problem with this device structure is that stronger SOTs require thinner magnets with thicknesses down to ~1 nm, but thinner magnets exhibit higher damping that results in high power consumption and poor performance. The proposed research will address this longstanding problem by simultaneously engineering strong SOTs and low damping in several-nm-thick, single-layer magnetic metal films. The research will take a fundamentally different approach to symmetry breaking, which is an essential ingredient for the emergence of SOTs. Specifically, in contrast to the conventional bilayers where symmetry is broken at film interfaces, the proposed approach deliberately breaks symmetry within the magnetic film itself – via a continuous compositional gradient along the thickness axis. Such bulk symmetry breaking is hypothesized to yield strong SOTs directly within a thick, low-damping magnetic film. The objectives of this research are to: (1) grow and characterize vertically graded magnetic films and determine how their compositions and structures impact SOTs and damping; and (2) quantify how the SOTs and damping of vertically graded magnets impact the performance of spintronic memories, oscillators, and spin-wave channels. A successful outcome of this research will enable transformative advances in SOT-driven devices – including two-orders-of-magnitude lower power dissipation, along with higher stability, higher signal output, and excellent compatibility with commercial fabrication processes. More broadly, this research will catalyze device development that leverages spin-orbit phenomena in graded materials, which have the potential to supersede heterostructures relying on atomically sharp interfaces.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.