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Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 5, 053906- p.Article in journal (Refereed) Published
Abstract [en]

We report on the origin of the anomalous temperature dependence of coercivity observed in some soft ferromagnets by studying the magnetic and electronic properties of FeZr films doped using ion implantation by H, He, B, C, and N. The anomalous increase of the coercivity with temperature was observed only in the C- and B-doped samples. Using x-ray photoelectron spectroscopy, we show that the anomalous behavior of the coercivity coincides with the occurrence of an electron charge transfer for those implanted samples. The origin of the anomaly is discussed in terms of (i) magnetic softness, (ii) nature of the Fe-C and -B covalent bonds, and (iii) large charge transfer. (C) 2014 AIP Publishing LLC.

Place, publisher, year, edition, pages
2014. Vol. 116, no 5, 053906- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-233598DOI: 10.1063/1.4892038ISI: 000341178900042OAI: oai:DiVA.org:uu-233598DiVA: diva2:754509
Available from: 2014-10-10 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Metallic Amorphous Thin Films and Heterostructures with Tunable Magnetic Properties
Open this publication in new window or tab >>Metallic Amorphous Thin Films and Heterostructures with Tunable Magnetic Properties
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The primary focus of this thesis is to study the effect of doping on magnetic properties in amorphous Fe100−xZrx alloys. Samples with compositions of x = 7,11.6 and 12 at.% were implanted with different concentrations of H. Moreover, the samples with a composition of x = 7 at.% were also implanted with He, B, C and N. Magnetic measurements were performed, using SQUID magnetometry and MOKE, in order to compare the as-grown and the implanted films. The Curie temperature (Tc) increases and the coercivity (Hc) decreases, with increasing dopant volume. We also found that Hc increases with temperature for B and C doped samples. Magnetization curves at low temperature validate the presence of non-collinear spin configurations in the as-grown films, which is suppressed after doping, resulting in films with tunable soft magnetic properties. We have also studied the effect of interlayer mixing and finite size effects on FeZr in Fe92Zr8/AlZr multilayer films, and found an anomalous increase of Tc with decreasing thickness.

Strain induced changes in the magnetization of an amorphous Co95Zr5 film at the orthorhombic phase transition of the BaTiO3 substrate, was also studied. The results show that structural modifications of the substrate increases the stress and hence changes the magnetic anisotropy in the amorphous Co95Zr5 layer.

Finally, the magnetization reversal of Co and CoX heterostructures, with X being Cr, Fe, Ni, Pd, Pt and Ru, has been studied. For this purpose a synthetic antiferromagnet structure, FM/NM/FM, was used, where FM is a ferromagnetic Co or CoX layer and NM is a nonmagnetic Ru spacer layer. The FM layers are coupled antiferromagnetically across the NM layer. For a range of FM layer thicknesses, the exchange stiffness parameter Aex and the interlayer coupling (JRKKY ) of the Co or CoX layers were obtained. This is done by fitting M(H) curves, measured by SQUID magnetometry, to a micromagnetic model. The alloying in CoX resulted in a decreasing Aex and also a reduced MS. The experimental results are in a good agreement with DFT calculations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 60 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1218
Keyword
Amorphous, Thin Film, Magnetic properties, FeZr alloys, Ion implantation
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-239950 (URN)978-91-554-9139-0 (ISBN)
Public defence
2015-02-27, 10134, Ångströmlaboratoriet, Polacksbacken, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2015-02-06 Created: 2015-01-04 Last updated: 2015-03-09Bibliographically approved

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Moubah, RedaAhlberg, MartinaZamani, AtiehOlsson, AndersHjörvarsson, BjörgvinJönsson, Petra E.

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