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Statics, Domain Structure and Dynamics in the Dilute Dipolar Magnet LiHoF4
KTH, School of Engineering Sciences (SCI), Theoretical Physics.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , v, 59 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:52
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-11166ISBN: 978-91-7415-424-5 (print)OAI: oai:DiVA.org:kth-11166DiVA: diva2:236761
Public defence
2009-09-25, Sal FD51, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100624Available from: 2009-09-25 Created: 2009-09-25 Last updated: 2010-07-05Bibliographically approved
List of papers
1. Phase diagram of the dilute magnet LiHoxY1-xF4
Open this publication in new window or tab >>Phase diagram of the dilute magnet LiHoxY1-xF4
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 5Article in journal (Refereed) Published
Abstract [en]

We study the effective long-range Ising dipole model with a local exchange interaction appropriate for the dilute magnetic compound LiHoxY1-xF4. Our calculations yield a value of 0.12 K for the nearest-neighbor exchange interaction. Using a Monte Carlo method, we calculate the phase boundary T-c(x) between the ferromagnetic and paramagnetic phases. We demonstrate that the experimentally observed linear decrease in T-c with dilution is not the simple mean-field result, but a combination of the effects of fluctuations and the exchange interaction. Furthermore, we find a critical dilution x(c)=0.21(2), below which there is no ordering. In agreement with recent Monte Carlo simulations on a similar model, we find no evidence of the experimentally observed freezing of the glassy state in our calculation. We apply the theory of Stephen and Aharony to LiHoxY1-xF4 and find that the theory does predict a finite-temperature freezing of the spin glass. Reasons for the discrepancies are discussed.

Keyword
LITHIUM HOLMIUM FLUORIDE, LIHOF4, RANGE, FERROMAGNETISM, ALGORITHM, GLASSES, SYSTEMS
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-13941 (URN)000249155100094 ()2-s2.0-34547994339 (Scopus ID)
Note

QC 20100705

Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2017-04-28Bibliographically approved
2. Low-temperature properties of the dilute dipolar magnet LiHoxY1-xF4
Open this publication in new window or tab >>Low-temperature properties of the dilute dipolar magnet LiHoxY1-xF4
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 5Article in journal (Refereed) Published
Abstract [en]

We analyze recent experiments on the dilute rare-earth compound LiHoxY1-xF4 in the context of an effective Ising dipolar model. Using a Monte Carlo method we calculate the low-temperature behavior of the specific heat and linear susceptibility and compare our results to measurements. In our model the susceptibility follows a Curie-Weiss law at high temperature, X similar to 1 / (T- T-cw), with a Curie-Weiss temperature that scales with dilution, T-cw similar to x, consistent with early experiments. We also find that the peak in the specific heat scales linearly with dilution, C-max(T)similar to x, in disagreement with recent experiments. This difference could be caused by the hyperfine interaction which is not included in our calculation. Experimental studies do not reach a consensus on the functional form of the susceptibility and specific heat, and in particular, we do not see reported scalings of the form X similar to T-0.75 and X similar to exp(-T/T-0). Furthermore, we calculate the ground-state magnetization as a function of dilution and re-examine the phase diagram around the critical dilution x, = 0.24 +/- 0.03. We find that the spin-glass susceptibility for the Ising model does not diverge below x, while some recent experiments give strong evidence for a stable spin-glass phase in LiHo0.167Y0.833F4.

Keyword
SPIN-GLASSES
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-13942 (URN)10.1103/PhysRevB.78.054437 (DOI)000259368200093 ()2-s2.0-50449103708 (Scopus ID)
Note
QC 20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2010-07-05Bibliographically approved
3. The ferromagnetic transition and domain structure in LiHoF4
Open this publication in new window or tab >>The ferromagnetic transition and domain structure in LiHoF4
2009 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, no 2Article in journal (Refereed) Published
Abstract [en]

Using Monte Carlo simulations we verify that the rare-earth compound LiHoF4 is a very good realization of a dipolar Ising model. With only one free parameter our calculations for the magnetization, specific heat and inverse susceptibility match experimental data at a quantitative level in the 0.5-3 kelvin range, including the ferromagnetic transition at 1.53 K. Using parallel tempering methods and reaching system sizes up to 32000 dipoles with periodic boundary conditions, we are able to give evidence of the logarithmic corrections predicted in renormalization group theory. Due to the long range and angular dependence of the dipolar model, sample shape and domains play a crucial role in the ordered state. We consider surface corrections to Griffiths's theorem, which arise infinite macroscopic samples and lead to a theory of magnetic domains. We find a domain wall energy of 0.059 erg/cm(2) and predict that the ground-state domain structure for cylinders with a demagnetization factor N > 0 consists of thin parallel sheets of opposite magnetization, with a width depending on the demagnetization factor.

Keyword
LITHIUM HOLMIUM FLUORIDE, CRITICAL-BEHAVIOR, LOGARITHMIC CORRECTIONS, COMPUTER-SIMULATION, MONTE-CARLO, MAGNET, PHASE, MODEL, CRYSTAL, DIPOLES
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-13943 (URN)10.1209/0295-5075/87/27007 (DOI)000269665400027 ()2-s2.0-79051468890 (Scopus ID)
Note
QC 20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2010-07-20Bibliographically approved
4. Glauber Dynamics of Dilute Ising Dipoles
Open this publication in new window or tab >>Glauber Dynamics of Dilute Ising Dipoles
(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-13944 (URN)
Note
QC 20100705Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2010-07-20Bibliographically approved

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