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Origin of Magnetic Anisotropy of Gd Metal
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.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2003 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 91, no 15, 157201-157204 p.Article in journal (Refereed) Published
Abstract [en]

Using first-principles theory, we have calculated the energy of Gd as a function of spin direction, θ, between the c and a axes and found good agreement with experiment for both the total magnetic anisotropy energy and its angular dependence. The calculated low temperature direction of the magnetic moment lies at an angle of 20° to the c axis. The calculated magnetic anisotropy energy of Gd metal is due to a unique mechanism involving a contribution of 7.5  μeV from the classical dipole-dipole interaction between spins plus a contribution of 16  μeV due to the spin-orbit interaction of the conduction electrons. The 4f spin polarizes the conduction electrons via exchange interaction, which transfers the magnetic anisotropy of the conduction electrons to the 4f spin.

Place, publisher, year, edition, pages
2003. Vol. 91, no 15, 157201-157204 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91745DOI: 10.1103/PhysRevLett.91.157201OAI: oai:DiVA.org:uu-91745DiVA: diva2:164576
Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Theory of Crystal Fields and Magnetism of f-electron Systems
Open this publication in new window or tab >>Theory of Crystal Fields and Magnetism of f-electron Systems
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A parameter free approach for the calculation of the crystal field splitting of the lowest Russel-Saunders J-multiplet in f-electron systems has been developed and applied to selected compounds. The developed theory is applicable to general symmetries and is based on symmetry constrained density functional theory calculations in the local density or in the generalised gradient approximation.

The magnetocrystalline anisotropy of Gd has been analysed. It has been shown that the peculiar orientation of the easy axis of magnetisation is consistent with an S-ground state. Further, the temperature dependence of the easy axis of magnetisation has been investigated and it has been shown that the temperature driven reduction of the effective magnetisation is the principal mechanism responsible for it.

A new method has been developed that allows for theoretical studies of the electronic structure and total energy of elements and compounds in an intermediate valence regime. The method combines model and first-principles band structure calculations, therefore being accurate and computationally efficient. It has been applied to Yb metal under pressure obtaining a remarkable agreement with experimental observations for the equation of state and the x-ray absorption spectroscopy.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 61 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 976
Keyword
Theoretical physics, Crystal Field, Magnetism, Electronic Structure, Teoretisk fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-4257 (URN)91-554-5963-3 (ISBN)
Public defence
2004-05-19, Polhemssalen, Ångström Laboratory, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:15
Opponent
Supervisors
Available from: 2004-04-28 Created: 2004-04-28Bibliographically approved
2. Transition Properties of f-electrons in Rare-earth Optical Materials
Open this publication in new window or tab >>Transition Properties of f-electrons in Rare-earth Optical Materials
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main purpose of this thesis is to theoretically study energy levels and intra-electronic transition intensities for various f-electron systems. The f-f electronic dipole transitions are parity-forbidden for a free ion but become non-zero when the ion is subject to a crystal-field. This is commonly described within the framework of Judd-Ofelt theory which accounts for the mixing of odd parity into the wave-functions.

Some refinements and quantitative studies have been made by applying many-body perturbation theory, or the perturbed functions approach, to obtain effective dipole operators due to correlation, spin-orbit and higher order crystal-field effects not included in Judd-Ofelt theory. A software for the computation of f-electron multiplets and Stark levels was implemented and published as well.

The single- and pair-functions used for the evaluation of intensity parameters were obtained by solving various inhomogeneous Schrödinger equations. The wave-functions and energies obtained by diagonalizing an effective Hamiltonian have been used together with the oscillator strength methods to simulate absorption spectrum. Consistent crystal-field parameters applied in some of the papers were obtained by fitting crystal polarizabilities to reflect the experimental Stark levels. The same crystal model was then used to generate odd crystal field parameters needed for the f-f transition intensities. The total effect of these refinements are spectral features that usually agree well with experimental findings. Some of these methods have also been applied and seen to be quite useful for the understanding of optical fiber amplifiers frequently used in today's optical networks.

Finally, a finite-difference approach was applied for the Helium iso-electronic sequence. The exact wave-function was expanded in a sum of partial waves, and accurate ground- and excited state energies were obtained by using the iterative Arnoldi approach.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 50 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 944
Keyword
Physics, rare-earth ions, oscillator strengths, correlation, crystal field, f-electrons, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-4014 (URN)91-554-5890-4 (ISBN)
Public defence
2004-03-19, Siegbahnsalen, Ångström laboratory, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 14:00
Opponent
Supervisors
Available from: 2004-02-25 Created: 2004-02-25 Last updated: 2012-04-04Bibliographically approved

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Ahuja, RajeevNordström, LarsEriksson, OlleBrooks, Michael S. S.

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