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Applied Physics Seminar: "Control of spin current polarization and spin-orbit torques by non-collinear antiferromagnetic order"

John Heron, Department of Materials Science and Engineering, University of Michigan
Wednesday, November 17, 2021
12:00-1:00 PM
340 West Hall Map
Bio:
Heron’s research focuses on understanding the role of symmetry in ferroic thin films and heterostructure interfaces to design and control spin-based phenomena. His work is supported by multiple federal agencies, the Semiconductor Research Corporation and has led to a technology being developed by Intel and a US start-up company.

Abstract:
Thin film antiferromagnets have emerged as strong candidates for state-of-the-art spintronic applications, promising efficient spin current generation that is critical for the development of low power non-volatile electronics. Intrinsic spin current generation in thin films has been primarily studied in systems with interfacial symmetry breaking (such as the Rashba-Edelstein effect), surface spin current from a topological insulator state, or a bulk spin Hall effect (via a large spin-orbit coupling and Berry curvature) in heavy metal systems such as W, Ta, or Pt. In general, the high symmetry of these non-magnetic systems limits the spin Hall conductivity tensor components to that of a left-handed polarization texture around the applied current direction and limits the spin current polarization injected into an adjacent magnetic layer to be a single in-plane direction. The ideal polarization direction for magnetic logic and memory devices is out-of-plane. In contrast, the reduced symmetry of non-collinear antiferromagnets allows for additional linear-response-driven spin conductivities, including longitudinal and out-of-plane spin currents with x, z polarization, though the measured effects so far have been small and non-tunable. Understanding the intrinsic origin of these out-of-plane spin currents with atypical polarization could enable new developments in low power non-volatile spin-based electronics.
Here I will discuss new multi-component out-of-plane spin Hall conductivities σx, σy, σz observed in L12 ordered antiferromagnetic PtMn3 thin films. Measurements across a collinear-noncollinear antiferromagnetic phase transition determine that these are uniquely generated in the non-collinear state. The maximum spin torque efficiencies (ξ = JS/Je ∼ 0.3) are found to be significantly larger than in Pt (ξ ∼ 0.1), a canonical spin Hall effect material. Additionally, the spin Hall conductivities in the non-collinear state exhibit an orientation-dependent anisotropy, which can be used to select for a dominant component. Our work motivates the symmetry control of spin transport for tailored functionality in magneto-electronic systems.
Building: West Hall
Event Type: Lecture / Discussion
Tags: Engineering, Physics
Source: Happening @ Michigan from Applied Physics