Dissertations / Theses: 'Ultrathin magnetic films'

1

Vaz, Carlos Antonio Fernandes. "Interface anisotropies in ultrathin magnetic films." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620969.

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2

Porrati, Fabrizio. "Spatially varying magnetic anisotropies in ultrathin films." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=967319277.

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3

Tselepi, Marina. "Atomic scale structure in ultrathin magnetic films." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624211.

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4

Cowburn, R. P. "Magnetic switching and domain structure in ultrathin epitaxial magnetic films." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598084.

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A detailed experimental study using magnetooptics has been performed into magnetic switching and domain structure predominantly in high quality ultrathin epitaxial Ag/Fe/Ag(001) films, for both in-plane and out of plane magnetisation. When the magnetisation is in-plane, magnetic switching has been found to proceed by a series of irreversible jumps of the magnetisation direction, each of which is mediated by the sweeping of domain walls. A simple phenomenological model has been developed which explains the switching and which highlights the role of magnetic anistropy and domain wall pinning by defects. Further micromagnetic modelling, combined with experiments, showed that the defects which determine coercivity are atomic steps on the Fe surface (named 'micropins'). A series of time resolved studies revealed that in addition to the micropins there also exists a second domain wall pinning mechanism, named 'macropinning' which is due to extrinsic defects such as scratches and other surface damage and which is not primarily responsible for coercivity. It has been found possible to engineer artificially the magnetic properties of a Permalloy film by introducing controlled macropins through lithographic structuring. The interplay between dipolar effects and intrinsic anisotropy leads to a novel domain structure during switching which could have important technological applications. In contrast to the in-plane magnetised case, in which the domain structure is an interim state which mediates the magnetic switching, the out of plane magnetised system was found to adopt a domain structure as its preferred ground state for certain temperatures and film thicknesses. These have been described by a magnetic phase diagram.

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Hope, S. "Spin polarised radiation studies of ultrathin magnetic films." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604219.

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Two distinct spin polarised radiation techniques have been employed to determine the magnetic properties of ultrathin magnetic films in-situ and ex-situ. The magneto-optical Kerr effect has been used to study the evolution of the magnetic properties during room temperature growth of Co/Cu(110) in -situ. The thickness dependence of the magnetic moment per atom in the Cu/Ni/Cu/Si(001) system has been investigated ex-situ using polarised neutron reflection. The Co/Cu(110) system is found to exhibit a 3D growth mode, becoming ferromagnetic at a critical thickness of d_c=4.6±1.1. ML. Remarkably, the magnetic susceptibility χ follows a power law near d_c with a critical exponent γ=2.39±0.08, which is in excellent agreement with the theoretical value of γ=2.43 for a 2D percolation phase transition. STM measurements on the same crystal indicate that the percolation phase transition is related to the coalescence of Co island clusters across the entire sample area. For a given Co thickness in the range 5MLCo<40ML the magnetic easy axis is found to switch through 90° over a repeatable duration (of the order of one hour) dependent on the thickness of the Co film. The behaviour is attributed to the reversal in sign of the effective uniaxial anisotropy constant, due to the adsorption of submonolayer quantities of residual CO gas in the UHV chamber. The effect of the adsorbed CO gas can be reversed by the adsorption of submonolayer coverages of Cu overlayer thereby switching the easy axis back to its original direction. For thin Co films (d_Co<15ML) the easy axis switches abruptly between the two directions. For thicker Co films (d_Co>15ML) the magnetic easy axis can take up intermediate directions and allows us to controllably engineer the direction of easy magnetisation at a constant Co thickness. A phenomenological model is developed to explain the switching behaviour based on competing uniaxial and cubic anisotropies. Depositing Co, or annealing the sample to 400K will produce similar behaviour. The nature of the switching for each mechanism is discussed.

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6

Freeland, D. J. "Role of morphology in ultrathin magnetic Fe films." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599205.

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Single crystal ultrathin Fe films have been grown on Ag(100), GaAs(100) and InAs(100) substrates, using MBE. As magnetic properties are highly dependent on the interface and morphology of surfaces, characterisation have been performed in-situ, to establish the correlation between magnetism and morphology. Epitaxial Fe has been deposited on GaAs(100)-4x6 at room temperature and the evolution of the phase transition from superparamagnetic to ferromagnetic has been studied. MOKE measurements indicate that after the onset of ferromagnetism, the whole Fe film is ferromagnetic and there are essentially no magnetically dead layers. This is in contrast with previous studies and indicates that, under certain conditions, the growth of Fe/GaAs(100) may not be complicated by interface alloying to the extent as previously thought. Whilst the lattice mismatch between Fe and InAs(100) is far greater than that for GaAs(100), epitaxial bcc Fe has been stabilised on InAs(100)-4x2. This system holds much promise for magneto-electronics since, unlike GaAs, InAs forms an ohmic contact with Fe. A uniaxial anisotropy has been observed in ultrathin, 5-10 ML Fe/InAs(100), grown at room temperature, with easy axis along [011]. This is in contrast to the far stronger uniaxial anisotropy in Fe/GaAs(100), whose easy axis is along the [01‾1] direction. Possible explanations for the differences between these systems are discussed. RHEED studies on Fe/InAs(100) have shown that there is a significant morphological relaxation, in the ultrathin 5-25 ML Fe region. Furthermore, relaxation occurs more rapidly along [01‾1] than along [011] - this 'anisotropic lattice relaxation' suggests magneto-elastic effects. LEED spotwidth measurements for Fe/Ag(001), indicate that there are two changes in surface morphology within the first seven monolayers of Fe growth. The coercivity thickness dependence is directly compared with LEED and discussed in terms of domain wall pinning at interfaces. Factors such as island growth, interdiffusion and segregation are highlighted to explain these structural and magnetic properties.

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7

Lew, Wen Siang. "Spin configurations and switching in ultrathin magnetic films." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620424.

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8

Guan, Wei. "Ultrathin films on semiconductor substrates: growth, magneto-optical characteristics and spin injection." Thesis, University of Salford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490413.

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Ferromagnetic metal films on semiconductors are considered to be one of the most likely candidates to achieve an efficient spin injection at room temperature, which is one of the essential requirements for spintronics devices. The work presented focused on a study of the ferromagnetic film-semiconductor heterostructures, especially their magneto-optical properties and spin injection.

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9

Di, Nan. "Electric and chemical manipulation of magnetic anisotropy of ultrathin ferromagnetic films." Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01224224/document.

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10

Song, Jiaming [Verfasser]. "Structural, electronic and magnetic properties of ultrathin epitaxial manganese films / Jiaming Song." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1077768214/34.

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11

Heide, Marcus. "Magnetic domain walls in ultrathin films contribution of the Dzyaloshinsky-Moriya interaction /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981517242.

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12

Skinta, John A. "Magnetic penetration depth studies of electron-doped cuprate and ultrathin YBCO films /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486459267521535.

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13

Wang, N. Y. N. "Optical spin injection and XMCD in ultrathin magnetic films deposited on GaAs." Thesis, University of Salford, 2009. http://usir.salford.ac.uk/26959/.

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The primary aim of this work is to study optically excited spin injection over a ferromagnetic metal-semiconductor Schottky barrier. A novel experimental approach has been introduced which enables the determination of the sign in the magnetic asymmetry of the photocurrent, hence the sign in the spin polarisation. The magnetic ultrathin films are grown on GaAs substrates using an e-beam evaporation technique in an ultrahigh vacuum system. The elemental and chemical characterisation of the Fe/GaAs samples has been conducted using x-ray absorption spectroscopy (XAS) whilst x-ray magnetic circular dichroism (XMCD) is utilised to obtain the magnetic information. The temperature-dependent magnetic properties of the samples are examined and the orbital, spin moments are estimated with classical optical sum rules. The magneto-optical Kerr effect (MOKE) is also employed to characterise the magnetic properties of ultrathin Ni, Fe films on GaAs substrates. The study of the spin injection processes is carried out with photoexcitation of electrons using circularly polarised light. Pure left and right circularly polarised light obtained using a Soleil-Babinet compensator plays a key role in the study of the spin injection processes. The influence of the magnetization of the ultra thin magnetic films on the chirality-dependent photocurrents is attributed to the effect of the spin-polarised density of states of the ferromagnetic films. Interestingly, under appropriate experimental conditions, a negative magnetic asymmetry in the photocurrent can be observed with Ni films, which are known to have a negative spin polarization for the electrons near the Fermi level. The study focuses on the use of a non-normal incidence experimental geometry in which various experimental factors are carefully explored. The influences of photon energy on the magnetic asymmetry in photocurrent have been examined providing a better understanding of the spin injection process.

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Nallan, Himamshu, Thong Ngo, Agham Posadas, Alexander Demkov, and John Ekerdt. "Area Selective Deposition of Ultrathin Magnetic Cobalt Films via Atomic Layer Deposition." Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-207142.

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The work investigates the selective deposition of cobalt oxide via atomic layer deposition. Methoxysilanes chlorosilane and poly(trimethylsilylstyrene) self-assembled monolayers are utilized to prevent wetting of water and cobalt bis(N-tert butyl, N'-ethylpropionamidinate) from the substrate, thereby controlling nucleation on the substrate and providing a pathway to enable selective deposition of cobalt oxide. Sr and Al are deposited atop the oxide films to scavenge oxygen and yield carbon-free cobalt metal films. Thermal reduction of the oxide layer in the presence of CO and H 2 was also investigated as an alternative. Finally, we demonstrate control over the tunability of the coercivity of the resultant films by controlling the reduction conditions.

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15

Rovinelli, Giovanni. "Magnetic, morphological and structural properties of polycrystalline ultrathin cobalt films for organic spintronics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

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The opportunity of using the organic molecules in spintronic devices appeared challenging since these materials, having nominally high spin relaxation times, are suitable for coherent spin manipulation. The spin behaviour in these molecular spintronic devices has been demonstrated to strongly depend on the nature of the chemical bonds between the organic molecules and the magnetic electrodes affecting also the magnetic response of both molecular and metallic sides. In particular, the adsorption of an organic molecule on a ferromagnetic layer has been proved to change the local magnetism of a magnetic substrate. In spite of their technological interest, the investigation of such effect in the case of the polycrystalline magnetic thin film is still lacking. My work contributes to filling this gap by studying the structural, morphological and magnetic properties of ultrathin polycrystalline cobalt films covered by the well-known buckminsterfullerene organic molecule (C60). The combined investigation by AFM, TEM, SQUID magnetometry and anisotropic magnetoresistance allowed to correlate the sample microstructure with the magnetic response and to identify the main mechanism responsible for spin transport in these FM layers. Analysed films are composed of polycrystalline cobalt grains decoupled by non-crystalline amorphous regions. The volume ratio between crystalline grains and amorphous regions increases by increasing the film thickness. As expected, the values of saturation magnetisation decrease as the crystallinity decreases and a typical blocking behaviour is present. The cobalt layers are also subjected to oxidation at the interface with the single crystal oxide substrate. The presence of amorphous phase in polycrystalline cobalt ultrathin film impacts the analysis of transport properties: the anisotropic magnetoresistance slightly depends on the crystalline phase while it is mainly inherent to the amorphous component.

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16

Liu, Yanwei. "A study of magnetic ultrathin films on GaAs and optically excited spin injection." Thesis, University of Salford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490537.

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Ferromagnetic metal - semiconductor Schottky diode structures are believed to be one of the most likely candidates to achieve an efficient spin injection at room temperature, which is one of the essential requirements for spintronic devices. rhe work presented has been performed with the aim of achieving a comprehensive understanding of the complicated spin-dependent transport processes taking place in the ferromagnetic metal-semiconductor Schottky diode structures.

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17

Chuang, Donna Sue. "Magnetic anisotrophy in ultrathin epitaxial films grown on surfaces vicinal to Cu(001)." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32145.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.
Vita.
Includes bibliographical references (leaves 115-119).
by Donna Sue Chuang.
Ph.D.

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18

McManus, Moyra Kathleen. "X-ray absorption fine structure measurements of the lattice strain in magnetic ultrathin films." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24332.pdf.

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19

Butterfield, Martin Thomas. "Surface structure of ultrathin metal films deposited on copper single crystals." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/33132.

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Ultrathin films of Cobalt, Iron and Manganese have been thennally evaporated onto an fcc Copper (111) single crystal substrate and investigated using a variety of surface structural teclmiques. The small lattice mismatch between these metals and the Cu (111) substrate make them an ideal candidate for the study of the phenomena of pseudomorphic film growth. This is important for the understanding of the close relationship between film structure and magnetic properties. Growing films with the structure of their substrate rather than their bulk phase may provide an opportunity to grow materials with novel physical and magnetic properties, and hence new technological applications. Both Cobalt and Iron have been found to initially maintain a registry with the fee Cu (111) surface in a manner consistent with pseudomorphic growth. This growth is complicated by island rather than layer-by-layer growth in the initials stages of the film. In both cases a change in the structure of the film seems to occur at a point where the coalescence of islands in the film may be expected to occur. When the film does change structure they do not form a perfect over-layer with the structure of their bulk counterpart. The films do contain a number of features representative of the bulk phase but also contain considerable disorder and possibly remnants of fcc (111) structure. The order present in these films can be greatly improved by annealing. Manganese appears to grow with an fee Mn (111) lattice spacing and there is no sign of a change in structure in films of up to 4.61 ML thick. The gradual deposition and annealing of a film to 300°C, with a total deposition time the same as that for a 1 ML thick film, causes a surface reconstruction to occur that is apparent in a R30° (√3×√3) LEED pattern. This is attributed to the formation of a surface alloy, which is also supported by the local expansion of the Cu lattice in the (111) direction.

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20

Pietzsch, Oswald. "Magnetic imaging by spin-polarized scanning tunneling spectroscopy applied to ultrathin Fe/W(110) films." [S.l.] : [s.n.], 2001. http://www.sub.uni-hamburg.de/disse/444/Disse.pdf.

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21

Romming, Niklas [Verfasser], and Roland [Akademischer Betreuer] Wiesendanger. "Discovery and Manipulation of Individual Skyrmions in Ultrathin Magnetic Films / Niklas Romming ; Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1150401516/34.

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22

Johnston, Hamish. "A study of the magnetic and structural properties of ultrathin Fe/Ni(111/W(110) films /." *McMaster only, 1997.

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23

Johnston, Hamish L. "A study of the magnetic and structural properties of ultrathin Fe/Ni(111)/W(110) films." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ30149.pdf.

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24

Perini, Marco [Verfasser], and Roland [Akademischer Betreuer] Wiesendanger. "Nanoscale non-collinear magnetic structures in Co-based epitaxial ultrathin films / Marco Perini ; Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/117936273X/34.

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25

Ott, Holger. "Magnetic structures and phase transitions in thin and ultrathin films of heavy lanthanide metals investigated by resonant magnetic X-ray scattering." [S.l. : s.n.], 2004. http://www.diss.fu-berlin.de/2004/186/index.html.

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26

Ramchal, Robert. "In situ magnetic domain imaging at the spin-reorientation transition of ultrathin Ni- and Fe/Ni-films." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=973910720.

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27

Ramchal, Robert Rabindranath. "In situ magnetic domain imaging at the spin-reorientation transition of ultrathin Ni- and Fe/Ni-films." Gerhard-Mercator-Universitaet Duisburg, 2005. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-01312005-175427/.

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In order to characterize the spin-reorientation transition (SRT), i. e. the change of the easy axis of the magnetization, of ultrathin Ni/Cu(100)- and Fe/Ni/Cu(100)-films the magnetic domain structure was imaged as a function of the Ni and Fe layer thickness, respectively, by using spin-polarized low energy electron microscopy (SPLEEM) during the film growth in ultrahigh vacuum at 300 K. Whereas the size of the domains at the SRT of Ni/Cu(100) is some micrometers, the domain structure of the Fe/Ni-films breaks up into a pattern of 180 nm wide stripe domains. It was shown that the SRT of both Ni/Cu(100) and Fe/Ni/Cu(100) proceeds via a spiral-like rotation of the magnetization within the domains. A discontinuous SRT via coexisting in-plane and out-of-plane magnetized stripe domains is not observed for the film systems.

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28

Kuhrau, Susanne [Verfasser], and Hans Peter [Akademischer Betreuer] Oepen. "Surface-sensitive magnetic imaging of polycrystalline and epitaxial ultrathin cobalt films with a perpendicular magnetic anisotropy / Susanne Kuhrau ; Betreuer: Hans Peter Oepen." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1197801227/34.

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29

Mann, Olivier Patrice. "Nanoscale electrodeposition of ultrathin magnetic Ni films and of the compound semiconductors AlSb and ZnSb from ionic liquids." Göttingen Cuvillier, 2007. http://d-nb.info/98745594X/04.

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30

Mann, Olivier Patrice. "Nanoscale electrodeposition of ultrathin magnetic Ni films and of the compound semiconductors AlSb and ZnSb from ionic liquids /." Göttingen : Cuvillier, 2008. http://d-nb.info/98745594X/04.

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31

von, Malottki Stephan [Verfasser], Stefan [Akademischer Betreuer] Heinze, Fabio [Gutachter] Caruso, and Hannes [Gutachter] Jónsson. "Stability of magnetic skyrmions in ultrathin films / Stephan von Malottki ; Gutachter: Fabio Caruso, Hannes Jónsson ; Betreuer: Stefan Heinze." Kiel : Universitätsbibliothek Kiel, 2020. http://d-nb.info/123127588X/34.

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32

Hagemeister, Julian Claudius [Verfasser], and Roland [Akademischer Betreuer] Wiesendanger. "Confinement effects and stability of spin-spirals and skyrmions in ultrathin magnetic films / Julian Claudius Hagemeister ; Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2017. http://d-nb.info/1139493078/34.

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33

Govind, Remya Kunjuveettil [Verfasser], Karl-Michael [Akademischer Betreuer] Schindler, Kathrin [Akademischer Betreuer] Dörr, and Clemens [Akademischer Betreuer] Laubschat. "Growth, magnetic properties and interface effects of Fe and Fe-oxide ultrathin films on BaTiO3(001) substrates / Remya Kunjuveettil Govind. Betreuer: Karl-Michael Schindler ; Kathrin Dörr ; Clemens Laubschat." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2013. http://d-nb.info/1045604151/34.

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34

Gray, S. J. "Structure and magnetism in ultrathin iron films." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599627.

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Fe films have been grown epitaxially on Ag(001) and GaAs(001) substrates. Ultra high vacuum conditions were used to allow the evolution of structural and magnetic properties to be studied during film growth. Structural characterisation was by LEED and RHEED and in situ magnetic characterisation by longitudinal MOKE and BLS. These techniques were further used to study the effect of Ag and Cr overlayers on 6 and 14 _ML Fe films. Some films were capped and further characterised ex situ by longitudinal and polar MOKE, and Kerr spectroscopy. Fe films deposited on Ag(001) were found to cover the substrate after approximately 4 _ML had been deposited. Quantitative analysis of the LEED patterns enabled step separations to be estimated. It was found that there was a minimum average step separation at 3 _ML Fe. The LEED patterns show pyramids, characteristic of growth dominated by Schwoebel barriers. In situ BLS and ex situ MOKE was used to study the evolution of the cubic and surface anisotropy constants K₁ and K_s with thickness. For very low thicknesses K₁ becomes just negative. At low temperatures thin Fe films are magnetised normal to the plane of the film. At higher temperatures an apparent gap in the magnetisation at the out-of-plane transition is seen. At higher temperatures still no remanent perpendicular magnetisation is seen. The gap and loss of remanent magnetisation are found to be due to domain formation. Ag deposited on Fe was found to show very little interaction, and all magnetic effects were saturated within 3 ML_.Cr deposition on Fe gave rise to changes in the surface anisotropy and magnetisation consistent with the antiferromagnetic nature of Cr with the first layer aligned antiparallel to the underlying Fe. This was seen on rougher Fe films.

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35

Schumann, Frank Oliver. "2D magnetism of ultrathin Co/Cu(100) films." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337385.

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36

Tetienne, Jean-Philippe. "Un microscope de champ magnétique basé sur le défaut azote-lacune du diamant : réalisation et application à l'étude de couches ferromagnétiques ultraminces." Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0037/document.

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La capacité à cartographier le champ magnétique à l'échelle nanométrique serait un atout crucial pour étudier les propriétés magnétiques des solides ainsi que certains phénomènes de transport, mais aussi pour des études fondamentales en biologie. Cette thèse porte sur la réalisation d'un microscope de champ magnétique d'un genre nouveau, qui promet une résolution spatiale de quelques nanomètres, une sensibilité de l'ordre du nanotesla, et fonctionne aux conditions ambiantes. Ce microscope est basé sur le défaut azote-lacune du diamant, dont les propriétés quantiques peuvent être exploitées pour en faire un magnétomètre ultrasensible de taille atomique. Dans un premier temps, nous présenterons le fonctionnement et la réalisation du microscope à défaut azote-lacune, qui consiste essentiellement en un microscope à force atomique sur la pointe duquel un nanocristal de diamant est attaché. Nous testerons le microscope en imageant le champ de fuite généré par un cœur de vortex dans un microdisque ferromagnétique. Dans un second temps, nous appliquerons le microscope à l'étude de couches ferromagnétiques ultraminces. Ces systèmes présentent un intérêt à la fois fondamental, les effets d'interfaces restant encore largement inexplorés à ce jour, et technologique, puisqu'ils sont à la base de propositions pour la réalisation de nouvelles mémoires magnétiques à basse consommation d'énergie. Nous étudierons d'abord la nature des parois de domaines dans ces couches ultraminces, ce qui nous permettra de révéler l'existence d'une interaction Dzyaloshinskii-Moriya d'origine interfaciale dans certains échantillons. Nous étudierons ensuite les sauts nanométriques d'une paroi de domaine induits par l'agitation thermique. Nous démontrerons en particulier le contrôle de ces sauts par un laser, ce qui nous permettra de visualiser et explorer le paysage énergétique de la paroi
The ability to map the magnetic field at the nanometer scale would be a crucial advance to study the magnetic properties of solids as well as some transport phenomena, but also for fundamental studies in biology. This thesis deals with the realisation of a magnetic field microscope of a new kind, which promises a spatial resolution down to a few nanometres, a sensitivity of the order of a few nanoteslas, and operates under ambient conditions. This microscope is based on the nitrogen-vacancy defect in diamond, whose quantum properties can be harnessed to make an ultrasensitive, atomic-size magnetometre. In the first part, we will present the basic principles and the realisation of the nitrogen-vacancy defect microscope, which consists essentially in an atomic force microscope on the tip of which a diamond nanocrystal is grafted. We will test the microscope by imaging the stray field generated by a vortex core in a ferromagnetic microdisk. In the second part, we will apply the microscope to the study of ultrathin ferromagnets. These systems are interesting both from the physical point of view, as interface effects have been little explored so far, and for technology, as they are the cornerstone of several proposals for realising novel magnetic memory devices with low energy consumption. We will first study the nature of domain walls in these ultrathin ferromagnets, which will enable us to reveal the existence of an interface-related Dzyaloshinskii-Moriya interaction in some samples. Next, we will study the nanometric jumps of a domain wall induced by thermal fluctuations. In particular, we will demonstrate control over these jumps using a laser, which will allow us to visualise and explore the wall's energy landscape

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37

Küpper, David. "Gas adsorption effects on magnetism and structure of ultrathin Co-based films." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612263.

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38

Finco, Aurore [Verfasser], and Roland [Akademischer Betreuer] Wiesendanger. "Interplay between non-collinear magnetism and nanoscale structural properties in epitaxial Fe-based ultrathin films / Aurore Finco ; Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/116301365X/34.

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39

Klimenta, Florian [Verfasser], H. L. [Akademischer Betreuer] Meyerheim, W. [Akademischer Betreuer] Hergert, and N. [Akademischer Betreuer] Jedrecy. "Preparation, geometric structure and magnetism of ultrathin oxide films on metal surfaces / Florian Klimenta. Betreuer: H. L. Meyerheim ; W. Hergert ; N. Jedrecy." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2013. http://d-nb.info/1036872424/34.

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40

Fruchart, Olivier. "Elaboration, étude et modélisation d'un système magnétique modèle : réseaux de plots sub-microniques ultraminces de Fe(110) épitaxié à anisotropie planaire." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10094.

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L'objectif de cette these etait l'elaboration, l'etude et la modelisation des processus de renversement de l'aimantation dans un systeme modele : des plots submicroniques ultraminces epitaxies a aimantation planaire. Nous avons montre en depot laser pulse (dlp) par analyse rheed et afm que le procede habituel de depot a t<800c des couches tampons de w et mo sur al#2o#3 induisait une rugosite importante. Nous proposons un nouveau procede fonde sur un depot a 200c, un recuit a 800c et une poursuite de depot a 800c, qui permet l'obtention de couches monocristallines de mo(110) dont la surface est composee de larges terrasses atomiques, permettant par consequent la croissance de couches de fer(110) de haute qualite. L'utilisation des techniques de lithographie x et de gravure seche ont ensuite permis de realiser des reseaux de dizaines de millions de plots (particules) identiques, de dimensions laterales de 200nm a 500nm. Pour les reseaux etudies les interaction dipolaires entre particules peuvent etre negligees. L'analyse magnetique des couches continues a montre que le systeme mo/fe(110) (peu etudie jusqu'alors) presente une anisotropie d'interface planaire qui favorise l'axe 001 au detriment de $$110, DE MEME INTENSITE MAIS DE SIGNE OPPOSE A CELLE DE W/FE(110), ET QUI PERMET D'ATTEINDRE DES CHAMPS D'ANISOTROPIE SUPERIEURS A 0. 5T AUX FAIBLES EPAISSEURS DE FE. AU DESSUS DE 10MC (MONOCOUCHES) LE RETOURNEMENT S'EFFECTUE A CHAMP FAIBLE PAR NUCLEATION SUR UN DEFAUT ISOLE PUIS PAR PROPAGATION LIBRE ET IMMEDIATE D'UNE PAROI. AU DESSOUS DE 5MC LES PAROIS SONT PIEGEES DU FAIT DES FLUCTUATIONS SPATIALES DISCRETES DE L'EPAISSEUR DE LA COUCHE DE FER. LA GRAVURE EN PARTICULES EMPECHE LE BALAYAGE DES PAROIS ET INDUIT UNE TRES FORTE AUGMENTATION DE COERCITIVITE, QUI EST D'AUTANT PLUS IMPORTANTE QUE L'EPAISSEUR EST FAIBLE (DU FAIT DE LA DIMINUTION DES CHAMPS DEMAGNETISANTS INTERNES AUX PARTICULES), JUSQU'A ATTEINDRE H#C = 0. 73H#A POUR E = 1NM. LE COMPORTEMENT HC() MESURE EST TRES PROCHE DE LA LOI DE STONER-WOHLFARTH, BIEN QUE LE RETOURNEMENT NE SOIT PAS COHERENT PUISQUE LE VOLUME DE NUCLEATION (DETERMINE PAR HC(T) ET TRAINAGE) NE REPRESENTE QUE 1% DU VOLUME D'UNE PARTICULE. DES MESURES DE PARTICULES INDIVIDUELLES PAR MICROSQUID CONFIRMENT QUE LES PARTICULES SONT ESSENTIELLEMENT UNIFORMEMENT AIMANTEES, ET MONTRENT EGALEMENT QUE LA DISTRIBUTION DES CHAMPS DE RETOURNEMENT D'UNE PARTICULE UNIQUE EST FAIBLE. NOUS PROPOSONS UNE METHODE POUR EVALUER LE CYCLE D'HYSTERESIS MOYEN D'UNE PARTICULE UNIQUE A PARTIR DE LA MESURE MACROSCOPIQUE DU CYCLE D'HYSTERESIS ET DE LA SUSCEPTIBILITE REVERSIBLE DU RESEAU. NOUS AVONS EGALEMENT DEVELOPPE UN MODELE MICROMAGNETIQUE DE RETOURNEMENT DE L'AIMANTATION SPECIFIQUE AUX PARTICULES ULTRAMINCES A AIMANTATION PLANAIRE, ET QUI PREDIT, EN FONCTION DE L'EPAISSEUR DU PLOT, LA REDUCTION DE CHAMP COERCITIF HC PAR RAPPORT AU CHAMP D'ANISOTROPIE, C'EST A DIRE PAR RAPPORT AU CHAMP DE RETOURNEMENT COHERENT. DES SIMULATIONS NUMERIQUES ONT MONTRE D'UNE PART LA PERTINENCE DU MODELE, D'AUTRE PART QU'AU DELA D'UNE TAILLE LATERALE DE L'ORDRE DE 50 A 100NM LA TAILLE LATERALE DU PLOT N'INFLUENCE PLUS LA VALEUR DE LA COERCITIVITE, QUI EST ALORS DETERMINEE UNIQUEMENT PAR L'EPAISSEUR DU PLOT. L'ACCORD EST RELATIVEMENT BON ENTRE MODELE ET SIMULATION D'UNE PART, EXPERIENCE D'AUTRE PART, MEME SI LA COERCITIVITE CALCULEE EST TOUJOURS PLUS ELEVEE QUE CELLE OBSERVEE.

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41

Makarov, Sergey [Verfasser], and Heiko [Akademischer Betreuer] Wende. "Magnetism of ultrathin Fe(001) films on Ir(001) inferred from in-situ 57Fe conversion electron Mössbauer spectroscopy in ultrahigh vacuum / Sergey Makarov. Betreuer: Heiko Wende." Duisburg, 2016. http://d-nb.info/1098130472/34.

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42

Lee, Kuo-Long, and 李國隆. "Magnetic Domains of NiO/Ni/Cu(001) Ultrathin Films." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/94779665096512271868.

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碩士
國立中正大學
物理系
99
The magnetic properties of a film of NiO/Ni/Cu(001) were investigated by using Magneto-Optical Kerr Effect (MOKE) , Photoemission Electron Microscopy (PEEM) at different temperature. The film was deposited by thermal evaporation of 13 ML Ni on Cu(001) substrate in an ultrahigh vacuum (UHV) chamber with a base pressure of 5×10-10 mbar and followed by oxygen exposure for 1800 Langmuir (L) . The growth of the film was monitored by using Medium-Energy Electron Diffraction (MEED) . The structure was resolved by using Low Energy Electron Diffraction (LEED) and IV-LEED. The surface oxide was confirmed by X-ray Absorption Spectroscopy (XAS) , where the peaks indicating NiO were found. Below the antiferromagnetic Néel temperature (TN) of the NiO, the coercivity of the film dramatically increases owing to the Antiferromagnet/Ferromagnet (AF/FM) exchange-biased coupling. From the PEEM images, it is found that the most NiO AF aligning along the perpendicular direction and canting direction driven by the perpendicular FM of Ni. Additionally, the films are protected by the surface oxide and can magnetically alive under the pressure of atmosphere. Thus, we successfully generate a film with perpendicular magnetic anisotropy that functions at the ambient condition. It might be applied for the spintronic devices.

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43

Chang, Y. C., and 張硯筑. "Study surface magnetic-optic properties of ultrathin films on dilute magnetic semiconductor." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/4a838j.

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碩士
國立嘉義大學
光電暨固態電子研究所
97
The magneto-optic properties of ultrathin films were studied by the surface magneto-optic effect in ultrahigh vacuum (UHV). It is one of main systems in our laboratory. There are two kinds of magneto-optic system: Faraday effect and Kerr effect. Generally, the surface magneto-optical Faraday effect (SMOFE) is used to measures the transparent substrate. Unlike the Kerr effect is used to measure the reflection signals. This thesis presents the details of the measurement and theory of Faraday effect, and the problems solved by the tool about ultrathin films on transparent substrate.. First, variation of magnetic properties of Co ultrathin films on ZnO(002) single crystal was studied by surface magneto-optic Faraday effect. Compare with the results of the magnetic properties and Auger spectra, we believed that the degree of surface roughness was strongly related to the magnetic properties signal. Then we began to investigate the low energy sputtering effect of N on the Co ultrathin films. So we suppose that the sputtering process let N or Co atom embed into the ZnO(002) surface. The surface composition might be N-ZnO or Co-ZnO compound. Finally, the interesting variations of coercive field and saturation magnetization of 0.55 nm Co/ZnO(002) with sputtering time in longitudinal-SMOFE measurement were observed. From the cross-link behaviors via the Auger spectra, we can rudely conclude the possible magnetic compound may be the Co4N .

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44

Porrati, Fabrizio [Verfasser]. "Spatially varying magnetic anisotropies in ultrathin films / von Fabrizio Porrati." 2002. http://d-nb.info/967319277/34.

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45

Huang, Shin-Hsueh, and 黃士學. "Characteristics of ultrathin CoFeB thin films with perpendicular magnetic anisotropy." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/71170250642387891439.

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碩士
國立雲林科技大學
材料科技研究所
99
In this study, we focused on the ultrathin CoFeB films with perpendicular magnetic anisotropy (PMA) which can be used for perpendicular magnetic tunnel junctions (pMTJs). The magnetic properties of the films were tuned by varying the CoFeB composition and the annealing temperatures. Two different compositions of CoFeB were studied: Co40Fe40B20 and Co20Fe60B20. At the first stage of the experiment, we fabricated both the bottom substructure Ta / CoFeB / MgO and the top structure MgO / CoFeB / Ta of pMTJs to look for conditions of PMA. The magnetic properties of the samples were measured by alternating gradient magnetometer (AGM). As for the annealing treatment, the samples were annealed at 300℃ and 350℃ with/without perpendicular applied magnetic field. The results show that the top structures Co40Fe40B20 of thickness 1.4 nm and 1.6 nm retained PMA for both as-deposition and post deposition annealing. The Co20Fe60B20 films of thickness from 1.2 nm to 1.6 nm had PMA from as-deposition condition to post annealing up to 300℃. In contrast with the bottom structures, no strong PMA was present for the top CoFeB structures. To overcome this problem, an ultrathin iron or magnesium layer was inserted between MgO and CoFeB layers. The results show that t adding Fe layer of thickness 0.2 nm together with the post annealing can enhance PMA of the top structures. In addition, we found that the bottom tantalum layer, served as the bottom electrode, becomes crystalline when sputtered on top of ruthenium layer. The crystallinity of tantalum can prevent intermix at Ta-CoFeB interface and reduce the thickness of magnetic dead layer of CoFeB after annealing treatment.

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46

阮家治. "Investigation of magnetic for Co ultrathin films on Fe/Pt(111)." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/33777072912265349614.

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47

Chiu, Chih-Lang, and 邱志郎. "Influence of Growth Temperature on Magnetic Properties in Magnetic Ultrathin fcc Co/Cu(100) Films." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/65148992669109376766.

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碩士
國立臺灣大學
物理學研究所
88
The crystal structure and magnetic properties, such as Curie temperature Tc, magnetic anisotropy are investigated for the fcc ultrathin magnetic films at variation of growth condition. All experiments are performed in an ultrahigh vacuum (UHV) multi-function chamber equipped with LEED, AES, in-situ MOKE, sputter gun, and film deposit. The Tc of 2 ML Co/Cu(100) rapidly drops down for the growth temperature Tg above 275 K. The Tc of Tg=225 K and Tg=325 K are 325 K and 250 K respectively, and the decrease on Tc is 30 %. The effects of growth condition on the Tc may be traced back to the morphology due to the various growth modes, bilayer island or layer-by-layer, and in turn the enhanced magnetic moment of the Co atoms at the edge of islands.

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48

"Tuning Anomalous Hall effect and Spin Polarized Current in Magnetic Ultrathin Films." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.51596.

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abstract: In this dissertation I studied the anomalous Hall effect in MgO/Permalloy/Nonmagnetic Metal(NM) based structure, spin polarized current in YIG/Pt based thin films and the origin of the perpendicular magnetic anisotropy(PMA) in the Ru/Co/Ru based structures. The anomalous Hall effect is the observation of a nonzero voltage difference across a magnetic material transverse to the current that flows through the material and the external magnetic field. Unlike the ordinary Hall effect which is observed in nonmagnetic metals, the anomalous Hall effect is only observed in magnetic materials and is orders of magnitude larger than the ordinary Hall effect. Unlike quantum anomalous Hall effect which only works in low temperature and extremely large magnetic field, anomalous Hall effect can be measured at room temperature under a relatively small magnetic field. This allows the anomalous Hall effect to have great potential applications in spintronics and be a good characterization tool for ferromagnetic materials especially materials that have perpendicular magnetic anisotropy(PMA). In my research, it is observed that a polarity change of the Hall resistance in the MgO/Permalloy/NM structure can be obtained when certain nonmagnetic metal is used as the capping layer while no polarity change is observed when some other metal is used as the capping layer. This allows us to tune the polarity of the anomalous Hall effect by changing the thickness of a component of the structure. My conclusion is that an intrinsic mechanism from Berry curvature plays an important role in the sign of anomalous Hall resistivity in the MgO/Py/HM structures. Surface and interfacial scattering also make substantial contribution to the measured Hall resistivity. Spin polarization(P) is one of the key concepts in spintronics and is defined as the difference in the spin up and spin down electron population near the Fermi level of a conductor. It has great applications in the spintronics field such as the creation of spin transfer torques, magnetic tunnel junction(MTJ), spintronic logic devices. In my research, spin polarization is measured on platinum layers grown on a YIG layer. Platinum is a nonmagnetic metal with strong spin orbit coupling which intrinsically has zero spin polarization. Nontrivial spin polarization measured by ARS is observed in the Pt layer when it is grown on YIG ferromagnetic insulator. This result is contrary to the zero spin polarization in the Pt layer when it is grown directly on SiO2 substrate. Magnetic proximity effect and spin current pumping from YIG into Pt is proposed as the reason of the nontrivial spin polarization induced in Pt. An even higher spin polarization in the Pt layer is observed when an ultrathin NiO layer or Cu layer is inserted between Pt and YIG which blocks the proximity effect. The spin polarization in the NiO inserted sample shows temperature dependence. This demonstrates that the spin current transmission is further enhanced in ultrathin NiO layers through magnon and spin fluctuations. Perpendicular Magnetic Anisotropy(PMA) has important applications in spintronics and magnetic storage. In the last chapter, I study the origin of PMA in one of the structures that shows PMA: Ru/Co/Ru. By measuring the ARS curve while changing the magnetic field orientation, the origin of the PMA in this structure is determined to be the strain induced by lattice mismatch.
Dissertation/Thesis
Doctoral Dissertation Physics 2018

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49

CHENG, W. Y., and 鄭文源. "Magnetic properties of Co/Ir(111) ultrathin films: growth and annealing effects." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/41992919475719057634.

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碩士
東海大學
物理學系
92
Magnetic properties of ultrathin Co films deposited on a Ir(111) surface at ambient temperature have been studied using surface magneto-optic Kerr effect technique. For Co/Ir(111) films thinner than 2 monolayers (ML), there is not magnetic hysteresis and the films are nonferromagnetic. As the Co thickness increases to above 2 ML, hysteresis occurs on both the longitudinal and polar configurations. The preferred orientation of magnetization for the films is neither on the surface nor perpendicular to the surface plane. Systematic investigations of the Co/Ir(111) films shows that perpendicular magnetic anisotropy (PMA) occurs after applying annealing treatment for films thinner than 4 ML. These results show that the Co/Ir system exhibits large technological potential in the applications of magnetic recording materials. As an example, significant interdiffusion occurs after annealing at temperature above 450 K for 3 ML Co/Ir(111) as revealed from Auger electron spectroscopy. Annealing treatment at higher temperatures results in a larger intermixing of Co and Ir at the surface layers. PMA occurs as the Auger intensity ratio (ICo/IIr) decreases to about half of the original value of the as-deposited film. Systemic investigations for the magnetic anisotropy of Co/Ir(111) system reveal a magnetic phase diagram for Co thickness up to 4 ML and annealing temperature up to 900 K. Regions of nonferromagnetic, PMA, and ferromagnetic phases were resolved. The relations between PMA and surface composition has been identified.

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50

Chen, Wei-Hsiang, and 陳暐翔. "Surface structure and related magnetic properties of Fe/Ir(111) ultrathin films." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/62390499298329817756.

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Dissertations / Theses on the topic 'Ultrathin magnetic films'

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