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Metallic Amorphous Thin Films and Heterostructures with Tunable Magnetic Properties
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
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 [en]
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: urn:nbn:se:uu:diva-239950ISBN: 978-91-554-9139-0 (print)OAI: oai:DiVA.org:uu-239950DiVA: diva2:775686
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
List of papers
1. Tuning magnetic properties by hydrogen implantation in amorphous Fe100-xZrx thin films
Open this publication in new window or tab >>Tuning magnetic properties by hydrogen implantation in amorphous Fe100-xZrx thin films
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2013 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 346, 138-141 p.Article in journal (Refereed) Published
Abstract [en]

Thin films of amorphous Fe100-xZrx (x=7.6-12.9 at%) were synthesized by dc-magnetron sputtering. Samples with compositions of x=11.6 and 12.0 at% were hydrogenated by implantation. The Curie temperature increases with hydrogen content from 232 K for as-grown Fe88Zr12 to 370 K for a sample hydrogenated to 31 at%. The coercivity decreases dramatically upon hydrogenation, yielding films with tunable transition temperatures and soft magnetic properties.

Keyword
FeZr alloy, Amorphous, Hydrogen, Ion implantation
National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-209151 (URN)10.1016/j.jmmm.2013.07.031 (DOI)000324311200024 ()
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved
2. Magnetic properties of light ion implanted amorphous Fe93Zr7 films
Open this publication in new window or tab >>Magnetic properties of light ion implanted amorphous Fe93Zr7 films
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-244342 (URN)
Available from: 2015-02-16 Created: 2015-02-16 Last updated: 2015-02-16Bibliographically approved
3. Soft Room-Temperature Ferromagnetism of Carbon-Implanted Amorphous Fe93Zr7 Films
Open this publication in new window or tab >>Soft Room-Temperature Ferromagnetism of Carbon-Implanted Amorphous Fe93Zr7 Films
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2013 (English)In: APPL PHYS EXPRESS, ISSN 1882-0778, Vol. 6, no 5, 053001- p.Article in journal (Refereed) Published
Abstract [en]

We report on the effect of carbon implantation on the structural, electronic, and magnetic properties of Fe93Zr7 (FeZr) amorphous films. Extended X-ray absorption fine structure measurements on (FeZr)(100-x)C-x (x = 0, 5.5, and 11) indicate the incorporation of carbon in the FeZr matrix, with an increase of the Fe-Fe distance by implanting carbon. X-ray photoelectron spectroscopy measurements reveal the creation of Fe-C bonds after implantation. A significant enhancement of the Curie temperature and decrease of the coercivity are observed in the carbon-implanted films. Moreover, the non collinear ferromagnetism of the as-grown FeZr film diminishes upon carbon implantation.

National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-202378 (URN)10.7567/APEX.6.053001 (DOI)000318778800029 ()
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2017-02-01
4. Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
Open this publication in new window or tab >>Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
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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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-233598 (URN)10.1063/1.4892038 (DOI)000341178900042 ()
Available from: 2014-10-10 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
5. Reversed interface effects in amorphous FeZr/AlZr multilayers
Open this publication in new window or tab >>Reversed interface effects in amorphous FeZr/AlZr multilayers
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 18, 184403- p.Article in journal (Refereed) Published
Abstract [en]

We report an anomalous enhancement of the critical temperature (T-c) when the thickness (d) of the magnetic layer is decreased from 60 to 20 angstrom in amorphous FeZr/AlZr multilayers. Further reduction of the thickness causes a decrease of T-c, as expected by finite-size scaling, while the magnetic moment decreases monotonically for all values of d. The increase of the critical temperature is attributed to a reversed interface effect where local changes in the nearest-neighbor distance and coordination number gives a higher effective magnetic coupling at the interfaces compared to the interior of the layer. We have successfully described the results within a model where such interface effects are combined with finite-size scaling.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-238398 (URN)10.1103/PhysRevB.90.184403 (DOI)000344487600002 ()
Available from: 2014-12-19 Created: 2014-12-12 Last updated: 2017-12-05Bibliographically approved
6. Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures
Open this publication in new window or tab >>Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures
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2013 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 3, no 2, 022113- p.Article in journal (Refereed) Published
Abstract [en]

A clear change in the magnetic anisotropy in a layer of amorphous Co95Zr5 is obtained at the orthorhombic phase transition of the BaTiO3 substrate. The use of an amorphous buffer layer between the ferroelectric substrate and amorphous magnetic film shows that bulk strain governs the change in themagnetic anisotropy of our ferromagnetic-ferroelectric heterostructure. Moreover, we show that the thermal magnetization curves exhibit anisotropic behavior.

National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-198053 (URN)10.1063/1.4792050 (DOI)000315596600013 ()
Available from: 2013-04-10 Created: 2013-04-08 Last updated: 2017-12-06Bibliographically approved
7. Effects of substitution on the exchange stiffness and magnetization of Co films
Open this publication in new window or tab >>Effects of substitution on the exchange stiffness and magnetization of Co films
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 23, 235408- p.Article in journal (Refereed) Published
Abstract [en]

An antiferromagnetically coupled FM/NM/FM (FM = ferromagnet, NM = normal metal) trilayer structure responds to an external magnetic field by the formation of a magnetic-moment spring within the FM layers. We show that the exchange stiffness (A ex) of an FM layer can be determined by fitting the field-dependent magnetization, M(H), of the FM/NM/FM trilayer to a micromagnetic model. Using this method, we have measured the exchange stiffness of thin-film Co alloyed with Cr, Fe, Ni, Pd, Pt, and Ru. The results show that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. The observed trends have been understood by material-specific modeling based on density functional theory within the local density approximation. The stiffness measurements are in agreement with Brillouin light scattering carried out on thicker Co films.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-239091 (URN)10.1103/PhysRevB.90.235408 (DOI)000348846500002 ()
Available from: 2015-01-05 Created: 2014-12-18 Last updated: 2017-12-05Bibliographically approved

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