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Best practice of extracting magnetocaloric properties in magnetic simulations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In this thesis, a numerical study of simulating and computing the magnetocaloric properties of magnetic materials is presented. The main objective was to deduce the optimal procedure to obtain the isothermal change in entropy of magnetic systems, by evaluating two different formulas of entropy extraction, one relying on the magnetization of the material and the other on the magnet's heat capacity. The magnetic systems were simulated using two different Monte Carlo algorithms, the Metropolis and Wang-Landau procedures. The two entropy methods proved to be comparably similar to one another. Both approaches produced reliable and consistent results, though finite size effects could occur if the simulated system became too small. Erroneous fluctuations that invalidated the results did not seem stem from discrepancies between the entropy methods but mainly from the computation of the heat capacity itself. Accurate determination of the heat capacity via an internal energy derivative generated excellent results, while a heat capacity obtained from a variance formula of the internal energy rendered the extracted entropy unusable. The results acquired from the Metropolis algorithm were consistent, accurate and dependable, while all of those produced via the Wang-Landau method exhibited intrinsic fluctuations of varying severity. The Wang-Landau method also proved to be computationally ineffective compared to the Metropolis algorithm, rendering the method not suitable for magnetic simulations of this type.

Place, publisher, year, edition, pages
2019. , p. 30
Series
FYSAST ; FYSMAS1097
Keywords [en]
Magnetocaloric effect, Thermodynamics, Statistical mechanics, Monte Carlo simulations, Metropolis algorithm, Wang-Landau method, Isothermal change in entropy, Adiabatic change in temperature, Numerical methods, Effective spin models
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-388356OAI: oai:DiVA.org:uu-388356DiVA, id: diva2:1332830
Educational program
Master Programme in Physics
Supervisors
Examiners
Available from: 2019-07-01 Created: 2019-06-28 Last updated: 2019-07-01Bibliographically approved

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