Physics and Astronomy, Department of
Date of this Version
Spin-dependent properties are the heart of spintronic devices. Spintronics exploits electron’s spin, in addition to charge, to process and store the information. Recently, antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics, where an AFM order parameter (the Néel vector) is exploited to control spin-dependent transport properties. Due to being robust against magnetic perturbations, producing no stray fields, and exhibiting ultrafast dynamics, antiferromagnets can serve as promising functional materials for spintronic applications.
Among antiferromagnets, high Néel temperature noncollinear antiperovskites ANMn3 (A = Ga, Ni, Sn, and Pt) are interesting due to their magnetic group symmetry supporting non-trivial spin-dependent transport phenomena. These materials have structural similarity to perovskites which allows their epitaxial deposition on perovskite substrates. Using symmetry analyses, first-principles methods based on density-functional theory, tight-binding Hamiltonian models, and magnetization dynamics techniques, this dissertation makes predictions and provides insights into different spin-dependent phenomena in non-collinear AFM antiperovskites. The results are as follow.
It is shown that the noncollinear AFM phase of the antiperovskites exhibits sizable anomalous Hall conductivity (AHC), while the phase has zero AHC by symmetry. The Néel vector can be switched on the picosecond timescale using a spin torque generated by a spin polarized charge current. The critical switching current density can be tuned by ANMn3 stoichiometry engineering.
It is demonstrated that the noncollinear AFM phase of GaNMn3 exhibits unconventional spin Hall conductivity, in addition to the conventional existing in the paramagnetic phase. Due to its out-of-plane spin polarization, spin Hall current exerts a spin torque that can switch out-of-plane magnetization in an adjacent ferromagnet. This unconventional spin torque has been realized experimentally using spin torque ferromagnetic resonance measurements carried out by our collaborators at University of Wisconsin-Madison.
It is shown that noncollinear AFM antiperovskites allow generation of a spin-polarized longitudinal charge current like ferromagnets. The magnitude of the net spin polarization depends on crystallographic direction. These results demonstrate that AFM antiperovskites can be used as a spin source, spin-torque generator, and information carrier in spintronic devices. Advisor: Evgeny Tsymbal
A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfilment of Requirements For the Degree of Doctor of Philosophy, Major: Physics and Astronomy, Under the Supervision of Professor Evgeny Tsymbal. Lincoln, Nebraska: December 2021 Copyright © 2021 Gautam Gurung