Spin dynamics in inhomogeneous and defected low dimensional systems
Loading...
DOI
Date
2018
Authors
Journal Title
Journal ISSN
Volume Title
Thesis supervisors
Reviewers
Publisher
Institute of Nuclear Physics Polish Academy of Sciences
License Type
Creative commons license
Abstract
Wybrane układy magnetyczne mogące służyć jako falowody dla fal spinowych zostały
zbadane pod względem konfiguracji równowagowych i wzbudzeń elementarnych. Wykryto
zlokalizowane stany o częstościach w przerwie wzbronionej i - co ciekawe - w paśmie fal
objętościowych na złączach łańcuchów spinowych w zależności od parametrów ich odd-
ziaływań. Stwierdzono brak fali przechodzącej na złączu ferromagnetycznych łańcuchów
spinowych sprzężonych oddziaływaniem antyferromagnetycznym. Używając oprogramowa-
nia do obliczeń mikromagnetycznych wyznaczono konfiguracje równowagowe oraz ksz-
tałty histerezy magnetycznej w łańcuchach płaskich eliptycznych cząstek magnetycznych.
Częstości i polaryzacje fal spinowych w takich łańcuchach zbadano za pomocą opro-
gramowania dostarczonego przez Wydział Fizyki i Nauk o Ziemi Uniwersytetu w Fer-
rarze. Mechanizm przełączania konfiguracji okazał się związany z falami spinowymi o
częstościach zdążających do zera (tzw. ”miękkimi” modami). Stwierdzono, że odzyskanie
konfiguracji antyferromagnetycznej w takich łańcuchach jest możliwe przez zmianę paramet-
rów anizotropii. Skonstruowano najprostszy dwuspinowy model makrospinów, zbadano
jego konfiguracje równowagowe oraz wykryto przejście, które będąc nieciągłym nie wykazuje
histerezy, zatem przejawia cechy przejścia drugiego rodzaju.
Selected systems of different size scales have been studied in view of their applicability as waveguides for spin waves in various frequency ranges. Localized interface states have been found within a band of propagative waves on a junction of two ferromagnetic chains in addition to bound states in the frequency gaps. Total reflection in the whole frequency range has been found on an interface of two such chains coupled via antiferromagnetic interactions. The magnetic ground states have been found with the use of a software for micromagnetic computations for elliptically shaped flat nanoparticles (macrospins) of permalloy arranged in 1D chains. Ranges of stability/metastability of particular configu- rations as well as the related magnetic hysteresis loops resulting from the dipolar intera- particle interactions have been delimited. The frequencies of low lying spin waves as well as the corresponding spin precession profiles in such chains have been obtained with a software provided by the Department of Physics and Earth Sciences of the University of Ferrara. The mechanisms of the configuration switching under a homogeneous external magnetic field have been shown to be related with softening of the appropriate spin waves. A possibility of recovery of the stable antiferromagnetic configuration has been predicted by varying the anisotropy of particles. A number of configurations in the simplest two-spin model of macrospin chain have been revealed as a function of the macrospins separation in the chain. An evidence of a discontinuous transformation without, however, a hysteresis has been found.
Selected systems of different size scales have been studied in view of their applicability as waveguides for spin waves in various frequency ranges. Localized interface states have been found within a band of propagative waves on a junction of two ferromagnetic chains in addition to bound states in the frequency gaps. Total reflection in the whole frequency range has been found on an interface of two such chains coupled via antiferromagnetic interactions. The magnetic ground states have been found with the use of a software for micromagnetic computations for elliptically shaped flat nanoparticles (macrospins) of permalloy arranged in 1D chains. Ranges of stability/metastability of particular configu- rations as well as the related magnetic hysteresis loops resulting from the dipolar intera- particle interactions have been delimited. The frequencies of low lying spin waves as well as the corresponding spin precession profiles in such chains have been obtained with a software provided by the Department of Physics and Earth Sciences of the University of Ferrara. The mechanisms of the configuration switching under a homogeneous external magnetic field have been shown to be related with softening of the appropriate spin waves. A possibility of recovery of the stable antiferromagnetic configuration has been predicted by varying the anisotropy of particles. A number of configurations in the simplest two-spin model of macrospin chain have been revealed as a function of the macrospins separation in the chain. An evidence of a discontinuous transformation without, however, a hysteresis has been found.
Description
Keywords
Citation
Sponsorship:
Grantnumber:
License Type
Attribution-NonCommercial-NoDerivatives 4.0 Międzynarodowe