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The Importance of Controlling Composition to Tailor the Properties of Magnetic Thin Films
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0001-9234-0907
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many physical properties, for example structural or magnetic, of a material are directly dependent on elemental composition. Tailoring of properties through highly accurate composition control is possible in thin films. This work exemplifies such tailoring.

A short review is given of the current status for research in the area of permanent magnets, focusing on rare earth element free alternatives, where FeNi in the L10 phase is a possible candidate. Epitaxial FeNi L10 thin films were successfully synthesized by magnetron sputtering deposition of monoatomic layers of Fe and Ni on HF-etched Si(001) substrates with Cu or Cu100-xNix/Cu buffers. The in-plane lattice parameter aCuNi of the Cu100-xNix buffer layer was tuned by the Ni content. Through matching of aFeNi to aCuNi, the strain state (c/a)FeNi was controlled, where c is the out-of-plane lattice parameter. The 001 reflection indicative of chemical order, as measured by resonant x-ray diffraction, was in most cases split in two peaks due to a composition modulation of Fe and Ni. This chemical disorder contributed to that the uniaxial magnetocrystalline anisotropy energy, KU≈0.35 MJ/m3, was smaller than predicted. In later experiments the composition modulation could partly be compensated for. Remaining discrepancies with respect to predicted KU values were attributed to additional disorder induced by surface roughness of the buffer layer.

The interface sharpness between Fe and Ni was explored by producing epitaxial symmetric multilayers with individual layer thicknesses n = 4-48 monolayers (ML). For n ≤ 8 ML the films had pure fcc structure, with antiferromagnetic Fe layers. For n ≥ 8 ML the Fe layers relaxed to bcc structure.

A combinatorial sputter chamber, which has the capability to deposit samples with composition and thickness gradients, was assembled. A model for simulation of composition and thickness across large substrates, for the conditions in this chamber, is presented. The model is verified by comparison to experimental data. Some challenges inherent in combinatorial sputtering are discussed, and two experimental studies employing the technique are presented as examples. These investigated magnetic and structural properties of Tb-Co films, with 7-95 at.% Tb, and of amorphous and crystalline ternary gradient Co-Fe-Zr films, respectively.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 126 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1445
Keyword [en]
FeNi, L10, X-ray diffraction, magnetic anisotropy, magnetron sputtering, thin film, permanent magnets, combinatorial materials science, amorphous materials, magnetic properties of thin films, chemical order
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-305523ISBN: 978-91-554-9735-4OAI: oai:DiVA.org:uu-305523DiVA: diva2:1039332
Public defence
2016-12-09, Polhemsalen, ​Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-11-18 Created: 2016-10-18 Last updated: 2016-11-28
List of papers
1. Resonant x-ray diffraction revealing chemical disorder in sputtered L10 FeNi on Si(0 0 1)
Open this publication in new window or tab >>Resonant x-ray diffraction revealing chemical disorder in sputtered L10 FeNi on Si(0 0 1)
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2016 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 40, 406002Article in journal (Refereed) Published
Abstract [en]

In the search for new rare earth free permanent magnetic materials, FeNi with a L1(0) structure is a possible candidate. We have synthesized the phase in the thin film form by sputtering onto HF-etched Si(001) substrates. Monatomic layers of Fe and Ni were alternately deposited on a Cu buffer layer, all of which grew epitaxially on the Si substrates. A good crystal structure and epitaxial relationship was confirmed by in-house x-ray diffraction (XRD). The chemical order, which to some part is the origin of an uniaxial magnetic anisotropy, was measured by resonant XRD. The 001 superlattice reflection was split in two symmetrically spaced peaks due to a composition modulation of the Fe and Ni layers. Furthermore the influence of roughness induced chemical anti-phase domains on the RXRD pattern is exemplified. A smaller than expected magnetic uniaxial anisotropy energy was obtained, which is partly due to the composition modulations, but the major reason is concluded to be the Cu buffer surface roughness.

Keyword
resonant x-ray diffraction, FeNi, L10, magnetron sputtering, chemical order, magnetic anisotropy, magnetic properties of thin film
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-305358 (URN)10.1088/0953-8984/28/40/406002 (DOI)000383804500014 ()27518923 (PubMedID)
Available from: 2016-10-18 Created: 2016-10-14 Last updated: 2016-10-24Bibliographically approved
2. Strain Engineering for Controlled Growth of Thin-Film FeNi L10
Open this publication in new window or tab >>Strain Engineering for Controlled Growth of Thin-Film FeNi L10
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-305521 (URN)
Available from: 2016-10-22 Created: 2016-10-18 Last updated: 2016-10-24
3. Composition, structure and magnetic properties of very thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)
Open this publication in new window or tab >>Composition, structure and magnetic properties of very thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-305519 (URN)
Available from: 2016-10-22 Created: 2016-10-18 Last updated: 2016-10-24
4. Tailoring anisotropy and domain structure in amorphous TbCo thin films through combinatorial methods
Open this publication in new window or tab >>Tailoring anisotropy and domain structure in amorphous TbCo thin films through combinatorial methods
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2016 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3, 035005Article in journal (Refereed) Published
Abstract [en]

We apply an in-plane external magnetic field during growth of amorphous TbCo thin films and examine the effects on the magnetic anisotropy and domain structure. A combinatorial approach is employed throughout the deposition and analysis to study a continuous range of compositions between 7–95 at.% Tb. Magnetometry measurements show that all samples have a strong out-of-plane anisotropy, much larger than any in-plane components, regardless of the presence of a growth field. However, magnetic force microscopy demonstrates that the growth field does indeed have a large effect on the magnetic domain structure, resulting in elongated domains aligned along the imprinting field direction. The results show that the anisotropy can be tuned in intricate ways in amorphous TbCo films giving rise to unusual domain structures. Furthermore the results reveal that a combinatorial approach is highly effective for mapping out these material properties.

Keyword
magnetic anisotropy, amorphous magnetic materials, magnetic properties of thin films, domain structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-269248 (URN)10.1088/0022-3727/49/3/035005 (DOI)000368096300005 ()
Funder
Swedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2015-12-18 Created: 2015-12-15 Last updated: 2016-10-24Bibliographically approved
5. Magnetic and structural characterization of CoFeZr thin films grown by combinatorial sputtering
Open this publication in new window or tab >>Magnetic and structural characterization of CoFeZr thin films grown by combinatorial sputtering
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-305520 (URN)
Available from: 2016-10-22 Created: 2016-10-18 Last updated: 2016-10-24

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