Enabling Gigantic Antiferromagnetic Spin Caloritronic Effects through Spin Heat Accumulation
Abstract
Motivation and Hypothesis: The field of spin caloritronics strives to understand the coupling of spin and heat currents in magnetic heterostructures to discover novel mate1ial systems with functional thermal properties. To date, the field of spin caloritronics focused primarily on magnetic heterostructures with ferro- or ferri-magnetic order, such as Pt/yttrium-iron-garnet bilayers. In these types of systems, the magnitude of spin caloritronic phenomena at room temperature is small because the average energies, group velocities, and mean-free-paths of spin-waves in magnetic insulators are all small. We seek to discover extraordinary magneto -thermal transport phenomena by investigating a new class of spin-caloritronic material systems that possess antiferromagnetic order. Spin-waves in antiferromagnetic materials can possess energies and group-velocities orders of magnitude larger than ferro- and ferri-magnetic insulators. However, many antiferromagnetic insulators are not expected to display large spin-caloritronic effects in the absence of a strong magnetic field because spin-wave branches with opposite angular momentum are degenerate, or nearly degenerate. We hypothesize that spin-heat-accumulation in the normal metal will break the degeneracy by preferentially heating only one of the spin-wave branches, thereby enabling gigantic spin-caloritronic effects in antiferromagnetic heterostructures. To test our hypothesis, we will use our recent breakthroughs in controlling and characterizing electronic thermal transport in metal systems to design structures that can efficiently generate spin heat accumulation at interfaces. Objective: The overarching objective of our project is to gain a fundamental understanding of how spin-heat accumulation at a normal-metal/magnetic-insulator impacts spin caloritronic phenomena. To reach this objective, we propose two specific tasks. (1) We will use time-domain thermoreflectance measurements to provide the first quantitative measurements of the spin-dependent electron-phonon coupling coefficient in ferromagnetic metals. The asymmetry in electron-phonon coupling for up and down electrons plays a dominant role in determining the magnitude of spin-heat accumulation that can exist in metal heterostructures, but no experimental measurements of this asymmetry currently exist. (2) Using a combination of ultrafast pump/probe and thermo-electrical transport measurements, we will investigate how spin-heat accumulation at a normal-metal/antiferromagnetic interface impacts interfacial spin and heat currents. Expected Outcomes and ARO Relevance: An experimental discovery that directly links spin caloritronic phenomena and spin heat accumulation will profoundly affect our understanding of how heat and spins are coupled at interfaces. This discovery may enable a new class of functional spin caloritronic devices based on antiferromagnetic order, thereby enabling a novel field of study that focuses on antiferromagnetic spin caloritronic phenomena. Therefore, our work will significantly impact a wide array of scientific communities, including materials scientists, electrical engineers, thermal scientists, and condensed matter physicists. Furthern10re, our novel ultrafast characterization methods will provide direct insight into the potential utility of spin caloritronic phenomena for both next-generation computing technologies and terahertz radiation based imaging/sensing technologies. Advances in these technology classes will enhance Army critical applications such as information supremacy and soldier performance augmentation.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1810364
Entities
People
- Richard B Wilson
Organizations
- Army Contracting Command
- United States Army
- University of California, Riverside