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Magnetic Monopole Current in Artificial Square Spin Ice
KTH, School of Engineering Sciences (SCI).
KTH, School of Engineering Sciences (SCI).
2014 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

Recent theoretical and experimental results have revealed the existence of magnetic monopoles, in the form of quasi particles, in both condensed matter known as spin ice, as well as in two-dimensional artificial versions of the same material. In this report a two-dimensional Ising model is first examined, then an artificial square spin ice model using a dipole approximation, only taking into account nearest and next nearest neighbors. The Metropolis algorithm is used to obtain the internal energy, specific heat capacity and entropy as functions of temperature. In the latter model the magnetic monopole concentration and monopole current is also simulated. The two models show similar quantitative behavior in the above mentioned physical quantities, and in comparison to previously published results. In the artificial square spin ice model, under the influence of a magnetic field, a rapidly decreasing monopole current is observed, which decreases faster for higher temperatures. The magnitude of the magnetic field plays a significant role in the generation of the monopole current, and no direct effect of the phase transitionis observed.

Abstract [sv]

Nya teoretiska och experimentella resultat har uppvisat förekomsten av magnetiska monopoler, i form av kvasi-partiklar, både i kondenserade material kallade spinn-is, och i tvådimensionella artificiella versioner av samma material. I den här rapporten undersöks först en tvådimensionell Isingmodell, därefter en artificiell kvadratisk spinn-is-modell med hjälpav en dipolapproximation, där hänsyn endast tas till närmaste och näst närmaste grannar. Metropolis-algoritmen används för beräkna energi, specifika värmekapaciteten och entropinsom funktioner av temperatur. I den senare modellen simuleras även monopolskoncentrationen och monopolsströmmen. De två modellerna uppvisar snarlikt kvantitativt beteende med avseende på ovan nämnda fysikaliska storheter, jämfört med varandra och tidigare publicerade resultat. Under inverkan av ett magnetfält observeras en snabbt avtagande monopolsström, i den artificiella kvadratiska spinn-is-modellen, som avtar snabbare med högre temperaturer. Storleken på det pålagda magnetfältet har markant betydelse för alstrande av monopolsströmmen, och ingen direkt effekt av fasövergången observeras.

Place, publisher, year, edition, pages
2014. , 26 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-154229OAI: oai:DiVA.org:kth-154229DiVA: diva2:756072
Educational program
Master of Science in Engineering -Engineering Physics
Examiners
Available from: 2014-10-16 Created: 2014-10-16 Last updated: 2014-10-16Bibliographically approved

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