Long-distance spin transport in disordered insulators and low-damping metals

University Of Denver, Denver CO

Investigators

Abstract

Non-Technical Abstract: The study of spin transport by excitation of collective magnetization is an important new frontier in condensed matter physics. Spin transport in magnetic insulators, metals, or carbon nanomaterials via degrees of freedom not simply carried by propagating electrons is proving to be fertile fundamental ground rich with potential technological innovation. New discoveries in these areas inform future nanoelectronic models that could one day replace current technologies. For example, a spin information conduit formed from a disordered magnetic insulator thin film could allow easy materials integration and an essential inter-connect in a future all-spin computer processor. Similarly, large spin-wave effects in low-damping metallic ferromagnets could provide new ways to generate the spin currents needed to drive such a processor. Optimized carbon nanotube network films offer potential for spin transport applications, but could convert waste heat to usable energy if their fundamental thermal and thermoelectric physics is better understood. This project explores the fundamental science of these potentially transformative advances. Technical Abstract: This project focuses on measuring spin and heat transport (and their interplay) across three classes of materials: disordered magnetic insulators, low-damping ferromagnetic metals, and single-wall carbon nanotube networks. Each of these explores new and potentially transformative directions. The study of spin transport in disordered magnetic insulators follows on preliminary results showing that spin transport, driven by the spin Hall effect and detected via the inverse spin Hall effect, is surprisingly efficient where antiferromagnetic correlations exist but in the absence of magnetic and structural long range order. Specific tasks in this area include: 1) initial tests of amorphous Cr2O3 and NiO, 2) detailed characterization of distance and geometry dependence, 3) effects of annealing of amorphous YIG, 4) understanding of thermal gradient dependence, 5) waiting time and aging experiments, and 6) direct testing for non-equilibrium spin thermal conductivity in the disordered magnetic films. Exploration of magnon-driven spin and heat transport and thermoelectric effects in low-damping metals focuses on the Co-Fe alloy system and is motivated by potentially dramatic new spincaloritronic effects. Specific tasks here include: 1) studies with the "standard" Zink Lab thermal isolation platform, 2) characterization of AMR, MTEP, PNE, and ANE, and 3) exploration of magnon-driven spin currents using e-beam lithographically defined thermal isolation structures. Finally, study of spin and heat transport in carbon nanomaterials leverages expertise in preparation and study of highly-tuned single-wall nanotube network films. Specific tasks here include: 1) study of Wiedemann-Franz "violation" and doping dependence of thermal conductivity, 2) designing more sensitive thermal isolation platforms, and 3) testing spin transport in the networks using a non-local spin valve geometry.