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Fabrication and study of inorganic and organic thin film magnets
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thin film magnets are very important for many kinds of electronic devices and play a crucial role to achieve optimum performance. Therefore an intense level of research is going on all around the world to fabricate advanced electronics devices using both new inorganic and organic thin-film magnets. Historically, most magnetic materials used for technological applications are based on inorganic materials and have been studied extensible up to now. Recently, however, organic or molecular magnets have opened a new prospective of thin film magnets which have begun to show promise, offering the possibility of light-weight flexible materials and devices that include magnetic functionality.

The research presented in this thesis is hence divided into two parts, where inorganic and organic magnets in thin films form were studied. The Ti/Ni multilayer system is studied as an inorganic magnet in the first part, whereas M(TCNE)x thin films were studied in the second part with M= Fe, Ni and TCNE is tetracynoethelene, an organic compound, and x~2.

The Ti/Ni multilayer is a potential candidate for industrial applications and also features solid-state amorphisation. Because of various interesting scientific and technological aspects of Ti/Ni multilayer structures, many structural properties and subsequent thermal stability studies have been extensively reported in the literature, but surprisingly few reports are available on the corresponding electronic and magnetic properties. The work in the present thesis is therefore focused on synthesis and systematic investigation of structural, electronic and magnetic properties of as prepared as well as annealed Ti/Ni multilayer structures and to establish correlation between them.

The second part of the thesis deals with organic-based molecular magnets of the M(TCNE)x type, where x~2, M = Fe, Ni and TCNE = tetracynoethelene. Fe(TCNE)x and Ni(TCNE)x have for the first time been fabricated as thin films, free of oxygen- and precursor-induced defects. The films were fabricated in situ under ultra high vacuum conditions using our group’s recently developed fabrication techniques for organic-based molecular magnets. The previously unknown electronic structure of these thin film magnets are presented in the thesis. Room temperature magnetic ordering was observed for thin films of Ni(TCNE)2, in stark contrast to earlier versions of the material (fabricated with the old methods and hence containing various defects). Room temperature magnetic ordering for a similar system, Ni2(TCNE), previously has been reported by another group, but it is clear that more studies are necessary to completely resolve the underlying mechanisms for the magnetic properties seen in these materials.

Place, publisher, year, edition, pages
Linköping: Institutionen för teknik och naturvetenskap , 2007. , 65 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1152
Keyword [en]
Physics, electronic, thin films, inorganic magnets, organic magnets
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-11442ISBN: 978-91-85895-20-5 (print)OAI: oai:DiVA.org:liu-11442DiVA: diva2:17866
Public defence
2007-12-14, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2012-11-21
List of papers
1. Correlation of structural, chemical and magnetic properties in annealed Ti/Ni multilayer structures
Open this publication in new window or tab >>Correlation of structural, chemical and magnetic properties in annealed Ti/Ni multilayer structures
2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, Vol. 97, no 4, 043509- p.Article in journal (Refereed) Published
Abstract [en]

Ti/Ni multilayer samples have been synthesized on float glass substrates using an electron-beam evaporation technique under ultrahigh vacuum conditions at room temperature. Grazing incidence x-ray diffraction (GIXRD) and grazing incidence x-ray reflectivity (GIXRR) techniques were used, respectively, to study structural modifications and to determine corresponding changes in microstructural parameters, such as individual layer thickness, interface roughness, and electron density due to annealing treatment. In addition to this, the chemical nature of the surface and interfaces of these samples were also studied using a depth profile x-ray photoelectron spectroscopy (XPS) technique. The GIXRD measurement show clear amorphization of the as-deposited multilayer sample annealed in the temperature range of 300–400 °C. The corresponding GIXRR measurement indicates the formation of a sufficiently thick layer of Ti–Ni at interfaces converting the Ti/Ni bilayer into a Ti/Ti–Ni/Ni trilayer multilayer structure. The precipitation of the Ti–Ni alloy phase at the interface in the case of samples annealed at 400 °C has been confirmed by XPS measurements. The magnetization behavior investigated using the magneto-optical Kerr effect technique clearly shows well the saturation magnetization behavior for all samples annealed up to 300 °C, while the sample annealed at 400 °C does not show saturation magnetization. The corresponding coercivity value (Hc) is also found to be changed drastically from 15.5 to 0.6 Oe. This observed magnetization behavior is discussed and correlated with structural and chemical changes in the multilayer structure.

Keyword
titanium alloys, nickel alloys, ferromagnetic materials, magnetic multilayers, electron beam deposition, vacuum deposition, annealing, amorphisation, interface roughness, electron density, Kerr magneto-optical effect, coercive force, magnetic hysteresis, X-ray diffraction, X-ray photoelectron spectra, titanium, nickel
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13113 (URN)10.1063/1.1835561 (DOI)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2010-06-14
2. High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer
Open this publication in new window or tab >>High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer
2006 (English)In: Applied Surface Science, ISSN 0169-4332, Vol. 253, no 5, 2572-2580 p.Article in journal (Refereed) Published
Abstract [en]

High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi3 and Ti2Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes.

Keyword
Ti/Ni multilayer structure; Annealing effect; Interfaces properties; Magnetization measurements; Resistivity measurements
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13114 (URN)10.1016/j.apsusc.2006.05.036 (DOI)
Available from: 2008-04-01 Created: 2008-04-01
3. Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation
Open this publication in new window or tab >>Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation
2006 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 15, no 1-2, 56-66 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents investigation of Ti–Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 °C using synchrotron radiation. For this purpose [Ti (50 Å)/Ni (50 Å)]X10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti–Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 °C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (≥400 °C) with the formation of TiNi, TiNi3 and Ti2Ni alloy phases.

The survey scans corresponding to 400, 500 and 600 °C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti–Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 °C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti–Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti–Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 °C confirms existence and BE position of observed Ni 3d satellite structure. The observed changes and modifications in the VB photoemission are discussed and interpreted in terms of structural changes at the interface due to annealing treatment.

Keyword
Ti/Ni multilayer; PES; Synchroctron radiation; Valence band; Annealing; Alloy phase formation
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13115 (URN)10.1016/j.elspec.2006.03.006 (DOI)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2010-06-14
4. Influence of Ti layer thickness on solid state amorphization and magnetic properties of annealed Ti/Ni multilayer
Open this publication in new window or tab >>Influence of Ti layer thickness on solid state amorphization and magnetic properties of annealed Ti/Ni multilayer
2007 (English)In: Journal of Physics Condensed Matter, ISSN 0953-8984, Vol. 37, no 19, 376210- p.Article in journal (Refereed) Published
Abstract [en]

Annealing induced SSR (solid state reaction) leading to amorphization and magnetic properties as a function of Ti layer thickness has been investigated using XRD (x-ray diffraction), GIXRR (grazing incidence x-ray reflectivity) and MOKE (magneto-optical Kerr effect) measurements. [Ti(t Å)/Ni(50 Å)] × 10 ML samples where t = 30, 50 and 70 Å have been prepared by using electron beam evaporation technique under ultra-high vacuum conditions at room temperature. The amorphization process was carefully studied using XRD and GIXRR techniques showing that the SSA (solid state amorphization) temperature gradually decreases with increasing Ti layer thickness. Corresponding MOKE measurements show a magnetic to non-magnetic transition near the amorphization temperature (TA) with annealing, for each of the Ti layer thicknesses, due to crystalline Ti–Ni alloy phase formation at interfaces. The saturation magnetization and coercivity were also modified with Ti layer thickness variation. In addition to this, anisotropy developed with Ti layer thickness and diminished with increasing annealing temperatures. All these magnetic changes due to Ti layer thickness variations are interpreted in terms of amorphization and micro-structural changes near the SSA temperature.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13116 (URN)10.1088/0953-8984/19/37/376210 (DOI)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2009-04-21
5. Room temperature magnetism in thin film nickel-tetracynoethylene
Open this publication in new window or tab >>Room temperature magnetism in thin film nickel-tetracynoethylene
(English)Manuscript (Other academic)
Abstract [en]

Room temperature magnetic ordering is reported in Ni-Tetracynoethelene (TCNE) thin films fabricated on gold substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film thickness and stoichiometry were obtained from x-ray photoelectron spectroscopy (XPS) measurements. XPS derived stoichiometry points to a 1:2 ratio between Ni and TCNE resulting in Ni(TCNE)x, x ~ 2. No evidence of pure Ni metal in the in situ grown films were present in the XPS and UPS measurements within the detection limits of the techniques.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13117 (URN)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2012-11-21
6. Electronic structure of thin film iron-tetracyanoethylene: Fe(TCNE)x
Open this publication in new window or tab >>Electronic structure of thin film iron-tetracyanoethylene: Fe(TCNE)x
Show others...
2009 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 95, no 1, 131-138 p.Article in journal (Refereed) Published
Abstract [en]

Thin film iron-tetracyanoethylene Fe(TCNE) x , x∼2, as determined by photoelectron spectroscopy, was grown in situ under ultra-high vacuum conditions using a recently developed physical vapor deposition-based technique for fabrication of oxygen- and precursor-free organic-based molecular magnets. Photoelectron spectroscopy results show no spurious trace elements in the films, and the iron is of Fe2+ valency. The highest occupied molecular orbital of Fe(TCNE) x is located at ∼1.7 eV vs. Fermi level and is derived mainly from the TCNE singly occupied molecular orbital according to photoelectron spectroscopy and resonant photoelectron spectroscopy results. The Fe(3d)-derived states appear at higher binding energy, ∼4.5 eV, which is in contrast to V(TCNE)2 where the highest occupied molecular orbital is mainly derived from V(3d) states. Fitting ligand field multiplet and charge transfer multiplet calculations to the Fe L-edge near edge X-ray absorption fine structure spectrum yields a high-spin Fe2+ (3d6) configuration with a crystal field parameter 10Dq∼0.6 eV for the Fe(TCNE) x system. We propose that the significantly weaker Fe-TCNE ligand interaction as compared to the room temperature magnet V(TCNE)2 (10Dq∼2.3 eV) is a strongly contributing factor to the substantially lower magnetic ordering temperature (T C ) seen for Fe(TCNE) x -type magnets.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17167 (URN)10.1007/s00339-008-5032-y (DOI)
Available from: 2009-03-07 Created: 2009-03-07 Last updated: 2015-05-18

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