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Magnetic moments and exchange interactions in Fe0.82Ni0.18/V bcc(001) multilayers
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, Theoretical Magnetism.
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.
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2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 9, p. 094421-Article in journal (Refereed) Published
Abstract [en]

The magnetic ordering and average magnetization of multilayers are greatly affected by the interface structure of the system. In this paper, interface effects are discussed, and their impact on the amplitude and period of the interlayer exchange coupling and the magnetic moments are investigated for the Fe0.82Ni0.18∕V body-centered-cubic (001) system. By modeling these effects by first principles calculations we find good agreement with experiments over the whole investigated range of layer thicknesses. In addition, as different interface effects give different fingerprints on the interlayer exchange coupling and magnetization, we are able to make an estimate of the interface structure of the different experimental samples by comparing experiment to theory.

Place, publisher, year, edition, pages
2004. Vol. 70, no 9, p. 094421-
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91263DOI: 10.1103/PhysRevB.70.094421OAI: oai:DiVA.org:uu-91263DiVA, id: diva2:163932
Available from: 2004-01-19 Created: 2004-01-19 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Growth and Magnetic Properties of Fe- and FeNi-based Thin Films and Multilayers
Open this publication in new window or tab >>Growth and Magnetic Properties of Fe- and FeNi-based Thin Films and Multilayers
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the growth and magnetic properties of thin films and multilayers. The samples were grown by magnetron sputtering, and characterized structurally mainly by x-ray diffraction and reflectivity. The magnetic characterization of the multilayers was done by magneto-optical Kerr technique, SQUID magnetometry and, in two samples, by neutron reflectometry.

Arrays of small elements of polycrystalline permalloy (FeNi alloy with 19 wt% Fe) are of interest as a component in non-volatile magnetic random access memories (MRAM). Here the shape dependence of the domain structure in such elements was studied by magnetic force microscopy (MFM) and in thin ring magnets the 'onion' state could be seen for the first time. Also, by post-annealing in hydrogen atmosphere the number of domains decreased in each element due to enhanced relaxation and defect reduction.

Furthermore, permalloy-based anisotropic magnetoresistance (AMR) in read heads are nowadays replaced by material combinations that have a giant magnetoresistance (GMR) effect. In this work Fe/V(001) and Fe0.82Ni0.18/V(001) superlattices, i.e. single-crystal-like multilayers, were investigated. These systems showed much smaller GMR effect compared to the Fe/Cr system. However, by introducing Ni into the Fe layers the magnetic anisotropy and the interlayer exchange coupling (IEC) decreased, thereby increasing the sensitivity, which is a key property for a magnetic sensor. The interface region showed a reduced magnetic moment, and the influence of the structural quality was modelled and investigated theoretically in the Fe0.82Ni0.18/V case. Also, in the Fe(2-3 ML)/V(x ML) superlattices (ML=monolayers) the transition temperature from long-range magnetic order to paramagnetic order oscillated with the V layer thickness (x) as a result of the oscillatory behaviour of the IEC.

The introduction of hydrogen in the non-magnetic layers of, for example, Fe/V(001) superlattices is a way to tune the IEC strength. Here the tuning was used as a tool to study the magnetic order in a low-dimensional magnet. At the critical hydrogen concentration <H/V>=0.022 the Fe layers in an Fe(2 ML)/V(13 ML) superlattice became decoupled. Then the system behaved as a two-dimensional Ising magnet with a finite ordering temperature of about 60 K.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. p. 62
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 927
Keywords
Physics, Sputter growth, Permalloy, Multilayer, Superlattice, Magnetism, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-3940 (URN)91-554-5849-1 (ISBN)
Public defence
2004-02-13, Polhemssalen, Ångström laboratoriet, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:15
Opponent
Supervisors
Available from: 2004-01-19 Created: 2004-01-19Bibliographically approved
2. Spin Dynamics and Magnetic Multilayers
Open this publication in new window or tab >>Spin Dynamics and Magnetic Multilayers
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Theoretical studies based on first-principles theory are presented for a number of different magnetic systems. The first part of the thesis concerns spin dynamics and the second part concerns properties of magnetic multilayers. The theoretical treatment is based on electronic structure calculations performed by means of density functional theory.

A method is developed for simulating atomistic spin dynamics at finite temperatures, which is based on solving the equations of motion for the atomic spins by means of Langevin dynamics. The method relies on a mapping of the interatomic exchange interactions from density functional theory to a Heisenberg Hamiltonian. Simulations are performed for various magnetic systems and processes beyond the reach of conventional micromagnetism. As an example, magnetization dynamics in the limit of large magnetic and anisotropy fields is explored. Moreover, the method is applied to studying the dynamics of systems with complex atomic order such as the diluted magnetic semiconductor MnGaAs and the spin glass alloy CuMn. The method is also applied to a Fe thin film and a Fe/Cr/Fe trilayer system, where the limits of ultrafast switching are explored. Current induced magnetization dynamics is investigated by calculating the current induced spin-transfer torque by means of density functional theory combined with the relaxation time approximation and semi-classical Boltzmann theory. The current induced torque is calculated for the helical spin-density waves in Er and fcc Fe, where the current is found to promote a rigid rotation of the magnetic order.

Properties of magnetic multilayers composed of magnetic and nonmagnetic layers are investigated by means of the Korringa-Kohn-Rostocker interface Green's function method. Multilayer properties such as magnetic moments, interlayer exchange coupling and ordering temperatures are calculated and compared with experiments, with focus on understanding the influence of interface quality. Moreover, the influence on the interlayer exchange coupling of alloying the nonmagnetic spacer layers with small amounts of a magnetic impurity is investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. p. x, 74
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 326
Keywords
Physics, magnetism, electronic structure, density functional theory, spin dynamics, spin-transfer torque, spin-density wave, multilayer, interface structure, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-8168 (URN)978-91-554-6944-3 (ISBN)
Public defence
2007-09-21, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15
Opponent
Supervisors
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2012-03-28Bibliographically approved

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Skubic, BjörnEriksson, OlleAndersson, GabriellaHjörvarsson, Björgvin

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