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Twengström, Mikael
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Publications (4 of 4) Show all publications
Giblin, S. R., Twengström, M., Bovo, L., Ruminy, M., Bartkowiak, M., Manuel, P., . . . Fennell, T. (2018). Pauling Entropy, Metastability, and Equilibrium in Dy2Ti2O7 Spin Ice. Physical Review Letters, 121(6), Article ID 067202.
Open this publication in new window or tab >>Pauling Entropy, Metastability, and Equilibrium in Dy2Ti2O7 Spin Ice
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2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 6, article id 067202Article in journal (Refereed) Published
Abstract [en]

Determining the fate of the Pauling entropy in the classical spin ice material Dy2Ti2O7 with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice-the dipolar spin ice model-predicts an ordering transition at T approximate to 0.15 K, but recent experiments by Pomaranski et al. suggest an entropy recovery over long timescales at temperatures as high as 0.5 K, much too high to be compatible with the theory. Using neutron scattering and specific heat measurements at low temperatures and with long timescales ( 0.35 K/10(6) s and 0.5 K/10(5) s, respectively) on several isotopically enriched samples, we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Furthermore, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez et al. are, after all, essentially correct: The short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235135 (URN)10.1103/PhysRevLett.121.067202 (DOI)000441021400016 ()30141658 (PubMedID)
Funder
Swedish Research Council, 2013-03968Stiftelsen Olle Engkvist Byggmästare, 2014/807
Note

QC 20180919

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-09-19Bibliographically approved
Twengström, M., Bovo, L., Gingras, M. J., Bramwell, S. T. & Henelius, P. (2017). Microscopic aspects of magnetic lattice demagnetizing factors. PHYSICAL REVIEW MATERIALS, 1(4), Article ID 044406.
Open this publication in new window or tab >>Microscopic aspects of magnetic lattice demagnetizing factors
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2017 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 1, no 4, article id 044406Article in journal (Refereed) Published
Abstract [en]

The demagnetizing factor N is of both conceptual interest and practical importance. Considering localized magnetic moments on a lattice, we show that for nonellipsoidal samples, N depends on the spin dimensionality (Ising, XY, or Heisenberg) and orientation, as well as the sample shape and susceptibility. The generality of this result is demonstrated by means of a recursive analytic calculation as well as detailed Monte Carlo simulations of realistic model spin Hamiltonians. As an important check and application, we also make an accurate experimental determination of N for a representative collective paramagnet (i.e., the Dy2Ti2O7 spin ice compound) and show that the temperature dependence of the experimentally determined N agrees closely with our theoretical calculations. Our conclusion is that the well-established practice of approximating the true sample shape with "corresponding ellipsoids" for systems with long-range interactions will in many cases overlook important effects stemming from the microscopic aspects of the system under consideration.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-220295 (URN)10.1103/PhysRevMaterials.1.044406 (DOI)000416582000002 ()
Note

QC 20171222

Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2018-05-02Bibliographically approved
Giblin, S. R., Twengström, M. & et al., .Pauling entropy, metastability and equilibrium in Dy2Ti2O7spin ice.
Open this publication in new window or tab >>Pauling entropy, metastability and equilibrium in Dy2Ti2O7spin ice
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-227046 (URN)
Note

QC 20180502

Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-05-02Bibliographically approved
Bovo, L., Twengström, M., Petrenko, O. A., Fennell, T., Gingras, M. J., Bramwell, S. T. & Henelius, P.Special temperatures in frustrated ferromagnets,.
Open this publication in new window or tab >>Special temperatures in frustrated ferromagnets,
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-227045 (URN)
Note

QC 20180502

Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-05-02Bibliographically approved
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