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Perpendicular magnetocrystalline anisotropy in tetragonally distorted Fe-Co alloys
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
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2006 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 3, 037205Article in journal (Refereed) Published
Abstract [en]

We report on the experimental realization of tetragonal Fe-Co alloys as a constituent of Fe(0.36)Co(0.64)/Pt superlattices with huge perpendicular magnetocrystalline anisotropy energy, reaching 210 mu eV/atom, and a saturation magnetization of 2.5 mu(B)/atom at 40 K, in qualitative agreement with theoretical predictions. At room temperature the corresponding values 150 mu eV/atom and 2.2 mu(B)/atom are achieved. This suggests that Fe-Co alloys with carefully chosen combinations of composition and distortion are good candidates for high-density perpendicular storage materials.

Place, publisher, year, edition, pages
2006. Vol. 96, no 3, 037205
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-75248DOI: 10.1103/PhysRevLett.96.037205OAI: oai:DiVA.org:uu-75248DiVA: diva2:103158
Available from: 2006-04-17 Created: 2006-04-17 Last updated: 2017-01-25Bibliographically approved
In thesis
1. A Structural Viewpoint of Magnetism in Fe and Co Based Superlattices
Open this publication in new window or tab >>A Structural Viewpoint of Magnetism in Fe and Co Based Superlattices
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to understand the properties of thin film devices, knowledge of the material's structure is essential. The work presented here combines magnetic and structural characterization of the systems studied to gain a deeper physical understanding. The magnetic properties have been studied with a combination of x-ray magnetic circular dichroism, SQUID magnetometry and magneto-optical Kerr effect. For the structural characterization, x-ray reflectivity and diffraction have been used, complemented by neutron diffraction and transmission electron microscopy.

One structural property that affects the magnetic moment in metal-on-metal superlattices is interdiffusion between the layers. This is discussed for bcc Fe/Co(001) and bcc Fe81Ni19/Co(001) superlattices. The effect of interdiffusion was seen as a large region of enhanced magnetic moments as compared to theoretical calculations, which assume perfectly sharp interfaces. For the Fe81Ni19/Co(001) superlattices the chemical interface region, as revealed by neutron diffraction, was in good agreement with the region of magnetic enhancement.

Another structural property that has been investigated is the strain in the magnetic layers. This does not affect the spin magnetic moment to a large extent. However the magnetocrystalline anisotropy and the orbital moment are affected by the presence of strain. The effects on the orbital moment from strain and interfaces for Fe in Fe/V superlattices was studied, and it was found that the two contributions were separable.

In this context the effect of strain on the out-of-plane magnetocrystalline anisotropy in FeCo/Pt has also been studied. The latter system is interesting from a technological perspective since tetragonally distorted FeCo alloys have the potential to be suitable new materials in computer hard drives.

Finally, a computer program, based on the Differential Evolution algorithm, to refine primarily x-ray reflectivity data, is presented.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 92 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 308
Keyword
Physics, Magnetism, Multilayer, Superlattice, X-ray magnetic circular dichroism, X-ray diffraction, X-ray reflectivity, Neutron diffraction, Structural refinement, Interfaces, Fysik
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-7886 (URN)978-91-554-6891-0 (ISBN)
Public defence
2007-06-01, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2011-11-17Bibliographically approved
2. Tailored Properties of Ferromagnetic Thin Films
Open this publication in new window or tab >>Tailored Properties of Ferromagnetic Thin Films
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic thin films and patterned nanostructures have been studied with respect to their magnetic properties using SQUID-magnetometry, magnetic force microscopy, electrical measurements, and micromagnetic calculations.

Properties of vortex domain walls, trapped in Permalloy nanowires with artificial constrictions, were investigated experimentally and by numerical calculations. In particular, the geometrical extent and strength of the pinning potential were evaluated. In these wires, long-range vortex domain wall displacement induced by spin polarized alternating currents was obtained numerically at reduced threshold current densities as compared with the direct current case. Due to the asymmetry of the energy potential, the long-range displacement direction is determined by the vortex chirality.

Strained FeCo/Pt superlattices with strong perpendicular anisotropy were investigated experimentally. The strain was controlled by varying the thickness of each alternating layer with monolayer precision and was found to have a dominating effect on the total anisotropy.

Epitaxial films of the diluted magnetic semiconductor (Ga,Mn)As were studied with focus on how the ferromagnetic transition temperature could be controlled by post-growth annealing. The ferromagnetic transition temperature was enhanced by approximately 85% for a Mn-doping concentration of 6% under certain conditions.

A method to manipulate micrometer sized magnetic particles on patterned arrays of elliptical Permalloy microstructures was studied. Controlled motion and separation of the magnetic particles were obtained using applied rotating magnetic fields. The domain structure of the elliptical elements was studied numerically.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2008. 97 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 579
Keyword
micromagnetics, domain wall, vortex, pinning potential, nanowire, spin dynamics, spin transfer torque, magnetic anisotropy, MFM, Permalloy, PMA, magnetic multilayer, Curie temperature, DMS, GaMnAs, magnetic bioseparation
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-9403 (URN)978-91-554-7353-2 (ISBN)
Public defence
2008-12-11, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2008-11-19 Created: 2008-11-19 Last updated: 2011-11-16Bibliographically approved

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Andersson, GabriellaWarnicke, PeterBjörck, MattsSanyal, BiplabChacon, CyrilZlotea, ClaudiaNordström, LarsNordblad, PerEriksson, Olle

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