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  • 1.
    Bhatt, Pramod
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Fabrication and study of inorganic and organic thin film magnets2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. Correlation of structural, chemical and magnetic properties in annealed Ti/Ni multilayer structures
    Öppna denna publikation i ny flik eller fönster >>Correlation of structural, chemical and magnetic properties in annealed Ti/Ni multilayer structures
    2005 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, Vol. 97, nr 4, s. 043509-Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    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
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-13113 (URN)10.1063/1.1835561 (DOI)
    Tillgänglig från: 2008-04-01 Skapad: 2008-04-01 Senast uppdaterad: 2010-06-14
    2. High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer
    Öppna denna publikation i ny flik eller fönster >>High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer
    2006 (Engelska)Ingår i: Applied Surface Science, ISSN 0169-4332, Vol. 253, nr 5, s. 2572-2580Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Ti/Ni multilayer structure; Annealing effect; Interfaces properties; Magnetization measurements; Resistivity measurements
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-13114 (URN)10.1016/j.apsusc.2006.05.036 (DOI)
    Tillgänglig från: 2008-04-01 Skapad: 2008-04-01
    3. Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation
    Öppna denna publikation i ny flik eller fönster >>Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation
    2006 (Engelska)Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 15, nr 1-2, s. 56-66Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Ti/Ni multilayer; PES; Synchroctron radiation; Valence band; Annealing; Alloy phase formation
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-13115 (URN)10.1016/j.elspec.2006.03.006 (DOI)
    Tillgänglig från: 2008-04-01 Skapad: 2008-04-01 Senast uppdaterad: 2010-06-14
    4. Influence of Ti layer thickness on solid state amorphization and magnetic properties of annealed Ti/Ni multilayer
    Öppna denna publikation i ny flik eller fönster >>Influence of Ti layer thickness on solid state amorphization and magnetic properties of annealed Ti/Ni multilayer
    2007 (Engelska)Ingår i: Journal of Physics Condensed Matter, ISSN 0953-8984, Vol. 37, nr 19, s. 376210-Artikel i tidskrift (Refereegranskat) 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.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-13116 (URN)10.1088/0953-8984/19/37/376210 (DOI)
    Tillgänglig från: 2008-04-01 Skapad: 2008-04-01 Senast uppdaterad: 2009-04-21
    5. Room temperature magnetism in thin film nickel-tetracynoethylene
    Öppna denna publikation i ny flik eller fönster >>Room temperature magnetism in thin film nickel-tetracynoethylene
    (Engelska)Manuskript (Övrigt vetenskapligt)
    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.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-13117 (URN)
    Tillgänglig från: 2008-04-01 Skapad: 2008-04-01 Senast uppdaterad: 2012-11-21
    6. Electronic structure of thin film iron-tetracyanoethylene: Fe(TCNE)x
    Öppna denna publikation i ny flik eller fönster >>Electronic structure of thin film iron-tetracyanoethylene: Fe(TCNE)x
    Visa övriga...
    2009 (Engelska)Ingår i: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 95, nr 1, s. 131-138Artikel i tidskrift (Refereegranskat) 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.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-17167 (URN)10.1007/s00339-008-5032-y (DOI)
    Tillgänglig från: 2009-03-07 Skapad: 2009-03-07 Senast uppdaterad: 2017-12-13
  • 2.
    Bhatt, Pramod
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Carlegrim, Elin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Kanciurzewska, A
    Adam Mickiewicz University Poznan.
    de Jong, M. P.
    University of Twente.
    Fahlman, Mats
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Electronic structure of thin film iron-tetracyanoethylene: Fe(TCNE)x2009Ingår i: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 95, nr 1, s. 131-138Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    Bhatt, Pramod
    et al.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    Chaudhari, S. M.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation2006Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 15, nr 1-2, s. 56-66Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Bhatt, Pramod
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Ganeshan, V.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    Reddy, V. R.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    Chaudhari, S. M.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer2006Ingår i: Applied Surface Science, ISSN 0169-4332, Vol. 253, nr 5, s. 2572-2580Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Bhatt, Pramod
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Kanciurzewska, Anna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Carlegrim, Elin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Kapilashrami, Mukes
    Division of Engineering Material Physics, Royal Institute of Technology, Stockholm, Sweden.
    Belova, Liubov
    Division of Engineering Material Physics, Royal Institute of Technology, Stockholm, Sweden.
    Rao, K V
    Division of Engineering Material Physics, Royal Institute of Technology, Stockholm, Sweden.
    Fahlman, Mats
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Ferromagnetism above room temperature in nickel–tetracyanoethylene thin films2009Ingår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 19, nr 36, s. 6610-6615Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Room temperature ferromagnetic ordering is reported in Ni–tetracyanoethylene (TCNE) thin films fabricated on Au substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables the preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film stoichiometry was 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 was present in the XPS or the ultraviolet photoelectron spectroscopy (UPS) measurements within the detection limits of the techniques.

  • 6.
    Bhatt, Pramod
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Rao, K. V.
    Division of Engineering Material Physics, Royal Institute of Technology, Stockholm, Sweden.
    Fahlman, Mats
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Room temperature magnetism in thin film nickel-tetracynoethyleneManuskript (Övrigt vetenskapligt)
    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.

  • 7.
    Bhatt, Pramod
    et al.
    Inter-University Consortium for DAE Facilities.
    Sharma, Anupam
    Inter-University Consortium for DAE Facilities, Indore, India.
    Chaudhari, S. M.
    Inter-University Consortium for DAE Facilities, Indore, India.
    Correlation of structural, chemical and magnetic properties in annealed Ti/Ni multilayer structures2005Ingår i: Journal of Applied Physics, ISSN 0021-8979, Vol. 97, nr 4, s. 043509-Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    Bhatt, Pramond
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Chaudhari, S. M.
    UGC-DAE Consortium for Scientific Research, Indore, India.
    Fahlman, Mats
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Influence of Ti layer thickness on solid state amorphization and magnetic properties of annealed Ti/Ni multilayer2007Ingår i: Journal of Physics Condensed Matter, ISSN 0953-8984, Vol. 37, nr 19, s. 376210-Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    Singh, Surendra
    et al.
    Bhabha Atom Research Centre.
    Basu, Saibal
    Bhabha Atom Research Centre.
    Bhatt , Pramod
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Structure and magnetism of Ni/Ti multilayers on annealing2008Ingår i: PRAMANA-JOURNAL OF PHYSICS, ISSN 0304-4289 , Vol. 71, nr 5, s. 1091-1095Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Neutron reflectometry study has been carried out in unpolarized (NR) and polarized (PNR) mode to understand the structure and magnetic properties of alloy formation at the interfaces of Ni/Ti multilayers on annealing. The PNR data from annealed sample shows a noticeable change with respect to the as-deposited sample. These changes are: a prominent shift of the multilayer Bragg peak to a higher angle and a decrease in the intensity of the Bragg peak. The PNR data from annealed sample revealed the formation of magnetically dead alloy layers at the interfaces. Changes in roughness parameters of the interfaces on annealing were also observed in the PNR data.

  • 10.
    Singh, Surendra
    et al.
    Bhabha Atom Research Centre.
    Basu, Saibal
    Bhabha Atom Research Centre.
    Bhatt, Pramod
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Poswal, A K
    Bhabha Atom Research Centre.
    Kinetics of alloy formation at the interfaces in a Ni-Ti multilayer: X-ray and neutron reflectometry study2009Ingår i: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 79, nr 19, s. 195435-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vacuum-deposited Ni/Ti multilayers on annealing at different temperatures exhibit formation of ordered alloy layers at interfaces. We have studied in detail the formation of alloy at interfaces of a Ni/Ti multilayer on annealing at 300 degrees C and 400 degrees C using powder x-ray diffraction, x-ray reflectometry, polarized neutron reflectometry, and off-specular x-ray reflectometry techniques. Correlation among structural, magnetic, and morphological properties in as-deposited Ni/Ti multilayer as well as in a sample annealed at 300 degrees C and 400 degrees C has been studied. X-ray diffraction technique was used to obtain crystal structure of the sample. Specular x-ray reflectometry and neutron reflectometry were used to determine the growth of alloy layers from density profile, as a function of depth in the sample. From off-specular x-ray reflectivity we found that the in-plane correlation lengths at the interfaces grew with annealing. This is associated with alloy crystallite growth obtained from x-ray reflectometry. Detailed magnetic-moment density profile of as-deposited as well as annealed multilayer sample has been determined by polarized neutron reflectometry measurements, which was used to determine the magnetic nature of the alloy layers. The results show formation of nonmagnetic alloy layers at the interfaces on annealing. From the Bragg-peak intensities of x-ray reflectivity and polarized neutron reflectivity measurements, we have estimated the diffusion lengths after annealing at 300 degrees C and 400 degrees C.

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