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The Low Temperature Magnetic Relaxation of Dy₂Ti₂O₇

dc.comment.hiddenA paper has been accepted to the journal Nature Physics that contains the results presented in this thesis. So we ask that the thesis be made available in 4 months, so that the work will be published before that time.en
dc.contributor.authorRevell, Halle
dc.date.accessioned2012-09-26T21:12:25Z
dc.date.available2012-09-26T21:12:25Z
dc.date.issued2012-09-26T21:12:25Z
dc.date.submitted2012
dc.description.abstractThe recent formulation of the monopole picture of spin ice[1, 2, 3], has lead to several studies of the signatures of monopole excitations[2, 4], as well as studies of the motion of magnetic monopoles[5, 6, 7]. In this thesis low temperature dynamics of the dipolar spin ice material Dy₂Ti₂O₇ are examined through SQUID measurements of the dc magnetic relaxation. The results are compared to recent ac susceptibility measurements[8] and new Monte Carlo simulations. It is found that instead of the relaxation being a single exponential decay with a temperature-activated relaxation time, which is what is expected from the dipolar spin ice model[9, 10, 11], the relaxation is a stretched exponential that develops into a long-time tail. The relaxation has a temperature-activated relaxation time, τ(T) = τo exp(∆E/kT), that has an energy barrier, ∆E/k, of ∼ 9K, as opposed to the ∼ 5 K energy barrier predicted by the dipolar spin ice model. By comparison to dynamic Monte Carlo simulations the stretched exponential behaviour is attributed to surface effects of the sample and the long-time tail is explained by a small amount (0.3 %) of stuffed Dy spins in the material. The 9 K energy barrier is explained by assuming that the basic spin flip process is not fully temperature independent and instead has an energy barrier of 4 K. This study should bring to light the importance of taking material defects and surface effects into account as one would in an electric conductor, whose material defects lead to resistance. Even in the case of the spin ice materials, which are usually assumed to be extremely “clean”, defects can play an important role in the dynamics and this study is the first instance where resistance meets “magneticity”.en
dc.identifier.urihttp://hdl.handle.net/10012/7042
dc.language.isoenen
dc.pendingfalseen
dc.publisherUniversity of Waterlooen
dc.subject.programPhysicsen
dc.titleThe Low Temperature Magnetic Relaxation of Dy₂Ti₂O₇en
dc.typeMaster Thesisen
uws-etd.degreeMaster of Scienceen
uws-etd.degree.departmentPhysics and Astronomyen
uws.peerReviewStatusUnrevieweden
uws.scholarLevelGraduateen
uws.typeOfResourceTexten

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