Computational Guiding Rules for the Design of Ultra-low Energy Spintronic Devices: Opportunities and Challenges

Voltage-induced magnetization switching can lead to a new paradigm enabling ultralow-power and high density nonvolatile MeRAM devices. Two major challenges for future MeRAM devices are to achieve large perpendicular magnetic anisotropy and high voltage-controlled magnetic anisotropy efficiency in heavy-metal/ferromagnet/insulator heterostructures.  First, I will present computational guiding rules for the design of ultralow energy spintronic devices where the heavy metal is across the 5d-transition metal series. The calculations reveal three important synergistic mechanisms to achieve low energy dissipation up to two orders of magnitude [1-4]. I will then discuss our recent work on antiferromagnetic resonance (AFMR) phenomena in metallic systems under an external electric field [5]. I will show that the AFMR linewidth can be separated into a relativistic component originating from the angular momentum transfer between the collinear AFM subsystem and the crystal through spin-orbit coupling, and an exchange component that originates from the spin exchange between the two sublattices. Both the AFMR linewidth, AFMR frequency and Néel temperature can be tuned by an external electric field. I will then present an ab initio-based theoretical framework which elucidates the origin of the bulk versus interface contributions to the spin-orbit torque (SOT) in heavy metal/ferromagnet bilayers [6-8] and reveals the microscopic mechanism for the recent experimental discovery of sign reversal of the field-like SOT due to interfacial Co oxidation. Finally I will discuss an ab-initio based Green's function approach to calculate the Dzyaloshinskii-Moriya interactions (DMI) that is computationally more efficient and accurate than the most commonly employed supercell and generalized Bloch-based approaches [9].