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Manipulating Spins in Antiferromagnets with External Forces

Tveten, Erlend Grytli
Doctoral thesis
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URI
http://hdl.handle.net/11250/2388130
Date
2016
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  • Institutt for fysikk [1751]
Abstract
This thesis presents five papers on theoretical spintronics. Four of the papers describe

antiferromagnets and the interactions between the magnetic order parameter and external

forces induced by charge currents, spin waves, magnetic fields, and stochastic

temperature fluctuations. The fifth paper studies the ultrafast magnetic response of a

ferromagnet after rapid heating by a laser pulse.

A significant part of the presented work is devoted to describing dynamics of the antiferromagnetic

order parameter. To this end, we develop the conceptually simple collective

coordinate equations of motion and demonstrate that the dynamics of antiferromagnetic

textures are equivalent to the inertial motion of classical particles subject

to external forces and dissipation-induced friction. We apply the collective coordinate

method to describe the dynamics of antiferromagnetic domain walls. First, we study

a domain wall under the influence of a charge current. Second, we describe the interactions

between a domain wall and antiferromagnetic spin waves and show that

the resulting domain wall dynamics depend crucially on the polarization of the spin

waves. Third, we demonstrate the possibility of accurately controlling the position

of an antiferromagnetic domain wall using external magnetic fields. The interactions

between inhomogeneous magnetic fields and antiferromagnetic domain walls result

from the intrinsic magnetization of textures in the order parameter.

By applying the fluctuation-dissipation theorem, we include finite temperature effects

to the dynamic equations of motion for a homogeneous antiferromagnet. We calculate

that the heat current between an antiferromagnetic insulator and an adjacent normal

metal is substantial and carried by a staggered spin current. We complete the transition

to the high-temperature regime by developing a theory of out-of-equilibrium ultrafast

spin dynamics in a ferromagnetic metal based on electron-magnon scattering.

The theory includes the effects from a nonthermalized magnon distribution function

and the out-of-equilibrium spin accumulation among the itinerant electrons.
Has parts
Paper 1: Tveten, Erlend Grytli; Qaiumzadeh, Alireza Javinani; Tretiakov, OA; Brataas, Arne. Staggered Dynamics in Antiferromagnets by Collective Coordinates. Physical Review Letters 2013 ;Volum 110.(12) http://dx.doi.org/10.1103/PhysRevLett.110.127208 (c) 2013 American Physical Society

Paper 2: Tveten, Erlend Grytli; Qaiumzadeh, Alireza; Brataas, Arne. Antiferromagnetic domain wall motion induced by spin waves. Physical Review Letters 2014 ;Volum 112.(14) http://dx.doi.org/10.1103/PhysRevLett.112.147204 (c) 2014 American Physical Society

Paper 3: Tveten, Erlend Grytli; Brataas, Arne; Tserkovnyak, Yaroslav. Electron-magnon scattering in magnetic heterostructures far out of equilibrium. Physical Review B. Condensed Matter and Materials Physics 2015 ;Volum 92:180412.(18) http://dx.doi.org/10.1103/PhysRevB.92.180412 (c) 2015 American Physical Society

Paper 4: Brataas, Arne; Skarsvåg, Hans Langva; Tveten, Erlend Grytli; Fjærbu, Eirik Løhaugen. Heat transport between antiferromagnetic insulators and normal metals. Physical Review B. Condensed Matter and Materials Physics 2015 ;Volum 92.(18) http://dx.doi.org/10.1103/PhysRevB.92.180414 (c) 2015 American Physical Society

Paper 5: Tveten, Erlend Grytli; Muller, Tristan; Linder, Jacob; Brataas, Arne. Intrinsic magnetization of antiferromagnetic textures. Physical Review B. Condensed Matter and Materials Physics 2016 http://dx.doi.org/10.1103/PhysRevB.93.104408 (c) 2016 American Physical Society
Publisher
NTNU
Series
Doctoral thesis at NTNU;2016:114

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