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Thermodynamics of a two-dimensional Heisenberg ferromagnet with dipolar interaction
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
2005 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 71, no 2, 024427- p.Article in journal (Refereed) Published
Abstract [en]

Thermodynamics of quantum and classical two-dimensional (2D) Heisenberg models with long-range dipole-dipole interaction has been investigated using various forms of self-consistent spin-wave theory (SSWT). It has been found that SSWT gives a much lower transition temperature T-c than the free-magnon (spin-wave) theory. For the classical spin, the T-c from SSWT lies within 9% of the Monte Carlo value, making SSWT the best approximation among those considered. It is proven that the random phase approximation vertex corrections to SSWT are rather small. The results depend strongly on the value of the spin, emphasizing the importance of using the quantum and not the classical 2D Heisenberg model even for large spins such as S=7/2.

Place, publisher, year, edition, pages
2005. Vol. 71, no 2, 024427- p.
Keyword [en]
ULTRATHIN MAGNETIC-FILMS, GREENS-FUNCTION THEORY, SPIN-WAVE THEORY, THIN-FILMS, REORIENTATION TRANSITION, LOW-TEMPERATURE, 2 DIMENSIONS, MONTE-CARLO, RANGE ORDER, ANISOTROPY
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-92687DOI: 10.1103/PhysRevB.71.024427OAI: oai:DiVA.org:uu-92687DiVA: diva2:165858
Available from: 2005-03-10 Created: 2005-03-10 Last updated: 2012-03-27Bibliographically approved
In thesis
1. Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding
Open this publication in new window or tab >>Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. Our calculations are done within the framework of the self-consistent spin-wave theory (SSWT), which is modified in order to include the dipolar interaction. Both quantum and classical versions of the Heisenberg model are considered.

The second part of the thesis investigates the chemical bonding in solids from the first principles calculations. A new chemical bonding indicator called balanced crystal orbital overlap population (BCOOP) is developed. BCOOP is less basis set dependent than the earlier indicators and it can be used with full-potential density-functional theory (DFT) codes. We apply BCOOP formalism to the chemical bonding in the high-T_c superconductor MgB2 and the theoretically predicted MAX phase Nb3SiC2. We also study how the chemical bonding results in a repulsive hydrogen–hydrogen interaction in metal hydrides. The role of this interaction in the structural phase transition in Ti3SnHx is investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. vii + 87 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 21
Keyword
Physics, spin Hamiltonians, quantized spin models, Heisenberg model, spin waves, self-consistent spin-wave theory, dipolar interaction, density functional theory, chemical bonding, overlap population, MAX phases, metal hydrides, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-4815 (URN)91-554-6164-6 (ISBN)
Public defence
2005-04-01, Siegbahnsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-03-10 Created: 2005-03-10Bibliographically approved

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Eriksson, Olle

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