Spin torque devices driven by tailored spin currents

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Spin electronics has the potential to revolutionize information technologies by providing energy-efficient magnetic devices for storage, processing, and transmission of information. Many of the existing and proposed devices rely on spin torques which are used to control magnetization dynamics and to manipulate magnetic states of nanoscale devices. The prominent examples are magnetic switching and spin torque oscillators. Spin torque oscillators can be used to create local microwave fields assisting the magnetic writing in hard drives. Furthermore, they can transmit information by emitting spin waves into a magnonic waveguide. Such oscillators exhibit a rich palette of nonlinear phenomena that makes them particularly attractive device candidates within the emerging paradigm of neuromorphic computing. The central prerequisite for the design and realization of spin torque devices is the energy-efficient generation of customized spin torques. Spin torques are exerted by spin currents injected into a magnetic device element. Currently, the major bottlenecks for the development of next generation devices are limitations to the polarization direction of pure spin currents and ohmic heating. The proposed research addresses these challenges, aiming to advance existing and to spark novel device concepts. The objective is to overcome the polarization constraints for pure spin currents and to utilize thermal effects for the generation of customizable spin torques. In the course of this research, graduate and undergraduate students will be trained in state-of-the-art experimental skills of device fabrications, material characterization, and magnetic spectroscopy. The proposal contains an outreach component that targets local school teachers who will receive training in electromagnetism and spintronics concepts. Moreover, an outreach program for a local science and arts event will be developed and presented to the students.The proposed approach utilizes spin-orbit torques in metallic ferromagnets (such as anomalous Hall effect and planar Hall effect) and furthermore investigates thermal spin injection via spin Seebeck effect in coupled two-ferromagnet systems. It is planned to fabricate nanowire devices from bilayers consisting of an insulating ferrimagnet and a metallic ferromagnet, where the latter serves as spin injector. Spin torque ferromagnetic resonance measurements will be carried out to assess spin dynamics in these coupled spin systems and to investigate the spin torques due to the spin-orbit and thermal effects. Furthermore, spin injectors with perpendicular and oblique spin polarizations will be engineered and implemented in novel spin-electronic applications, such as perpendicular spin torque oscillators, spin superfluid conveyors, and antiferromagnetic planar switches. The research will result in engineering concepts for spin-charge and spin-heat transducers and stimulate the development of novel magneto-electronic devices. It will, furthermore, provide incentive experimental data for further development of fundamental concepts in the areas of spin-orbitronics and spin-caloritronics. The devices developed in the course of the proposed research will serve the proof-of-concept and prototypical purposes.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.