Literature on magnetism

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  • A new model to describe the crossover from superparamagnetic to blocked magnetic nanoparticles, E. De Biasi et al. (2008)
    TitleA new model to describe the crossover from superparamagnetic to blocked magnetic nanoparticles
    AuthorsE. De Biasi, R.D. Zysler, C.A. Ramos, M. Knobel
    PublicationJournal of Magnetism and Magnetic Materials
    DateJuly 2008
    AbstractA new model that considers the thermal probability of uniform magnetization inversion in magnetic nanoparticles is presented. We included the temporal window in consideration of the thermal average, which allowed us to take into account the hysteretic behavior, leading to a more clear description of the passage from one regime to another. From this formalism appears a superparamagnetic probability L that indicated the fraction of superparamagnetic particles we find on the ensemble at a given T, H and experimental time window. We have performed numerical simulations, including different time windows and considering the high- and low-temperature regimes. We compare our model with the analytic solution in zero and high-temperature limits and find that the proposed model agrees with the simulations. Measurements of field-cooling and zero-filed-cooling magnetization as well as hysteresis loops were simulated applying this model, from which relevant considerations regarding the importance, applicability and limitations of this treatment could be obtained.
  • A micromagnetic study of domain-structure modeling, Tetsuji Matsuo et al. (2008)
    TitleA micromagnetic study of domain-structure modeling
    AuthorsTetsuji Matsuo, Naoki Mimuro, Masaaki Shimasaki
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    Date18 April 2008
    AbstractTo develop a mesoscopic model for magnetic-domain behavior, a domain structure model (DSM) was examined and compared with a micromagnetic simulation. The domain structure of this model is given by several domains with uniform magnetization vectors and domain walls. The directions of magnetization vectors and the locations of domain walls are determined so as to minimize the magnetic total energy of the magnetic material. The DSM was modified to improve its representation capability for domain behavior. The domain wall energy is multiplied by a vanishing factor to represent the disappearance of magnetic domain. The sequential quadratic programming procedure is divided into two steps to improve an energy minimization process. A comparison with micromagnetic simulation shows that the modified DSM improves the representation accuracy of the magnetization process.
  • Connection between microstructure and magnetic properties of soft magnetic materials, G. Bertotti (2008)
    TitleConnection between microstructure and magnetic properties of soft magnetic materials
    AuthorG. Bertotti
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    Date7 April 2008
    AbstractThe magnetic behavior of soft magnetic materials is discussed with some emphasis on the connection between macroscopic properties and underlying micromagnetic energy aspects. It is shown that important conceptual gaps still exist in the interpretation of macroscopic magnetic properties in terms of the micromagnetic formulation. Different aspects of hysteresis modeling, power loss prediction and magnetic non-destructive evaluation are discussed in this perspective.
  • Similarity rules of magnetic minor hysteresis loops in Fe and Ni metals, S. Takahashi et al. (2008)
    TitleSimilarity rules of magnetic minor hysteresis loops in Fe and Ni metals
    AuthorsS. Takahashi, S. Kobayashi, Y. Kamada, T. Shishido
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Corrected Proof
    Date16 March 2008
    AbstractWe have studied similarity rules of quasistatic minor hysteresis loops for Fe and Ni single crystals in the wide temperature range from 10 to 600�K. Two similarity rules of MR*/Ma*~3/4 and WR*/WF*~1/6, were found in a medium field range where irreversible movement of Bloch walls plays a crucial role for magnetization; Ma*, MR*, WF*, and WR* are magnetization, remanence, hysteresis loss, and remanence work of a minor hysteresis loop. The similarity rules hold true, being almost independent of kinds of ferromagnets, applied stress, and temperature. The origin was discussed from the viewpoint of pinning effects due to dislocations as well as eddy current effects which become predominant at low temperatures for samples with low dislocation density.
  • Structural and magnetic features of heterogeneously nucleated Fe-oxide nanoparticles, K. Simeonidis et al. (2008)
    TitleStructural and magnetic features of heterogeneously nucleated Fe-oxide nanoparticles
    AuthorsK. Simeonidis, S. Mourdikoudis, I. Tsiaoussis, M. Angelakeris, C. Dendrinou-Samara, O. Kalogirou
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
  • Angular dependence of coercivity of grains in nanocrystalline permanent magnets, Gong Yi-Min et al. (2008)
    TitleAngular dependence of coercivity of grains in nanocrystalline permanent magnets
    AuthorsGong Yi-Min, Lan Zhi-Huan, Yan Yu, Du Xiao-Bo, Wang Wen-Quan, Wang Xue-Feng, Su Feng, Lu Lei, Zhang Zhi-Sheng, Jin Han-Min, Wen Ge-Hui
    PublicationChinese Physics B
    AbstractIn this paper magnetization remanence curves were studied for nanocrystalline Pr8Fe87B5, Pr12Fe82B6 and Pr15Fe77B8. Initially the sample was at remanence following saturation along z-axis. After rotating the magnet by 5n degrees (n = 0, 1, ..., 18) a field H was applied along z-axis and then decreased to zero, and the remanence Jnr was measured as a function of H. The curves were compared with those calculated based on the nucleation of reverse domain model and domain wall pinning model. The latter model succeeds in simulation much better than the former, and it is concluded that the magnetization reversal is dominated by domain wall pinning for all the samples. The nucleation mechanism contribution, while remains small, increases with the increase of Pr content.
  • Implementation of Hysteresis Material Characteristics in Finite Element Computations, P. Sergeant et al. (2007)
    TitleImplementation of Hysteresis Material Characteristics in Finite Element Computations
    AuthorsP. Sergeant, L. Dupré
    Conference NameCOMSOL Users Conference 2007
    AbstractThe hysteresis loss in a sample is obtained by evaluating the drag force profile when slowly moving the sample forward and backward through the strong field of a permanent magnet. A numerical time-stepping model is presented that calculates the drag force profile. At every time step, the sample is slightly moved relative to the magnet. The model is based on 2D-FE computations (COMSOL AC/DC module, magnetostatics, perpendicular currents) including magnetic hysteretic material behavior using the Preisach model. The material behavior is described through differential permeabilities. The drag force is obtained by using the Maxwell stress tensor. A study was carried out of the numerical accuracy, and the model was also validated by comparing with measurements. The results show that the method is able to detect defects in the sample.
  • Tuning the domain wall orientation in thin magnetic strips using induced anisotropy, S. Cherifi et al. (2007)
    TitleTuning the domain wall orientation in thin magnetic strips using induced anisotropy
    AuthorsS. Cherifi, R. Hertel, A. Locatelli, Y. Watanabe, G. Potdevin, A. Ballestrazzi, M. Balboni, S. Heun
    PublicationApplied Physics Letters
    AbstractThe authors report on a method to tune the orientation of in-plane magnetic domains and domain walls in thin ferromagnetic strips by manipulating the magnetic anisotropy of the system. Uniaxial in-plane anisotropy is induced in a controlled way by oblique evaporation of magnetic thin strips. A direct correlation between the magnetization direction and the domain wall orientation is found experimentally and confirmed by micromagnetic simulations. The domain walls in the strips are always oriented along the oblique evaporation-induced easy axis, irrespective of the shape anisotropy. The controlled manipulation of domain wall orientations could provide promising possibilities for recently proposed devices based on domain wall propagation
  • About Coercivity and Intrinsic Coercivity, Magnetic Component Engineering (2007)
    TitleAbout Coercivity and Intrinsic Coercivity
    AuthorMagnetic Component Engineering
    PublisherMagnetic Component Engineering
    AbstractIn this article we will discuss a magnet's coercivity and intrinsic coercivity so as to give the reader a grasp of what these terms are and how they relate to permanent magnets. There is ample confusion about these terms, therefore, this article was written to give a better understanding of what these really mean with regards to the performance of permanent magnets and how these values should be specified on drawings.
  • Magnetic-based microfluidic platform for biomolecular separation, Qasem Ramadan et al. (2006)
    TitleMagnetic-based microfluidic platform for biomolecular separation
    AuthorsQasem Ramadan, Victor Samper, Daniel Poenar, Chen Yu
    PublicationBiomedical Microdevices
    DateJune 11, 2006
    AbstractA novel microfluidic platform for manipulation of micro/nano magnetic particles was designed, fabricated and tested for applications dealing with biomolecular separation. Recently, magnetic immunomagnetic cell separation has attracted a noticeable attention due to the high selectivity of such separation methods. Strong magnetic field gradients can be developed along the entire wire, and the miniaturized size of these current-carrying conductors strongly enhances the magnetic field gradient and therefore produces large, tunable and localized magnetic forces that can be applied on magnetic particles and confine them in very small spots. Further increases in the values of the generated magnetic field gradients can be achieved by employing miniaturized ferromagnetic structures (pillars) which can be magnetized by an external magnetic field or by micro-coils on the same chip. In this study, we demonstrate magnetic beads trapping, concentration, transportation and sensing in a liquid sample under continuous flow by employing high magnetic field gradients generated by novel multi-functional magnetic micro-devices. Each individual magnetic micro-device consists of the following components: 1. Cu micro-coils array embedded in the silicon substrate with high aspect ratio conductors for efficient magnetic field generation 2. Magnetic pillar(s) made of the magnetic alloy NiCoP for magnetic field focusing and magnetic field gradient enhancement. Each pillar is magnetized by its corresponding coil 3. Integrated sensing coil for magnetic beads detection 4. Microfluidic chamber containing all the previous components. Magnetic fields of about 0.1 T and field gradients of around 300 T/cm have been achieved, which allowed to develop a magnetic force of 3 10−9 N on a magnetic particle with radius of 1 μm. This force is large enough to trap/move this particle as the required force to affect such particles in a liquid sample is on the order of ∼pN. Trapping rates of up to 80% were achieved. Furthermore, different micro-coil designs were realized which allowed various movement modes and with different step-sizes. These results demonstrate that such devices incorporated within a microfluidic system can provide significantly improved spatial resolution and force magnitude for quick, efficient and highly selective magnetic trapping, separation and transportation, and as such they are an excellent solution for miniaturized μ-total analysis systems.
  • Analytical description of magnetization curves, Zdzislaw Wlodarski (2006)
    TitleAnalytical description of magnetization curves
    AuthorZdzislaw Wlodarski
    PublicationPhysica B: Condensed Matter
    DateMarch 15, 2006
    AbstractMagnetization process is described by the two-component expression based on the Brillouin equation and the Rayleigh model. Such approach leads to very accurate approximation of typical main magnetization curves, and adequate approximation of related hysteresis loops and demagnetization curves in the whole range of magnetization. Model parameters may be determined from the measured magnetization curves or standard physical parameters of magnetic materials.
  • Microcoils for transport of magnetic beads, Qasem Ramadan et al. (2006)
    TitleMicrocoils for transport of magnetic beads
    AuthorsQasem Ramadan, Chen Yu, Victor Samper, Daniel Puiu Poenar
    PublicationApplied Physics Letters
    DateJanuary 16, 2006
  • Cofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane), Adam C. Siegel et al. (2006)
    TitleCofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane)
    AuthorsAdam C. Siegel, Sergey S. Shevkoplyas, Douglas B. Weibel, Derek A. Bruzewicz, Andres W. Martinez, George M. Whitesides
    PublicationAngewandte Chemie International Edition
  • On-chip micro-electromagnets for magnetic-based bio-molecules separation, Qasem Ramadan et al. (2004)
    TitleOn-chip micro-electromagnets for magnetic-based bio-molecules separation
    AuthorsQasem Ramadan, Victor Samper, Daniel Poenar, Chen Yu
    PublicationJournal of Magnetism and Magnetic Materials
    AbstractThis paper reports a comprehensive theoretical, finite element and measurement analysis of different designs of planar micro-electromagnets for bio-molecular manipulation. The magnetic field due to current flowing in complex shapes of current-carrying conductors have been calculated analytically, simulated using finite-element analysis (FEA), and measured using the superconducting quantum interference device technique (SQUID). A comparison of the theoretical and measured magnetic field strength and patterns is presented. The planar electromagnets have been fabricated using patterned Al 2 [mu]m thick. The aim of the study is to explore and optimize the geometrical and structural parameters of planar electromagnets that give rise to the highest magnetic fields and forces for magnetic micro-beads manipulation. Magnetic beads are often used in biochemical assays for separation of bio-molecules. Typical beads are 0.2-10 [mu]m in diameter and have superparamagnetic properties. Increasing the intensity of the magnetic field generated by a coil by injection a larger current is not the most suitable solution as the maximum current is limited by Joule heating. Consequently, in order to maximize the field for a given current, one should optimize the geometry of the coil, as this is an extremely significant factor in determining the magnetic field intensity in 2D planar designs. The theoretical and measured results of this work show that the meander micro-electromagnet with mesh-shaped winding profile produces the strongest magnetic field (about 2.7 [mu]T for a current intensity of 6 mA) compared with other meander designs, such as the serpentine and rosette-shaped ones. The magnetic fields of these three types of meander-shaped micro-electromagnets were compared theoretically with that produced by a spiral micro-electromagnet whose technological realization is more complicated and costly due to the fact that it requires an additional insulation layer with a contact window and a second patterned metal layer as a via. Nevertheless, the spiral design produces a much stronger magnetic field up to five times larger than that of the mesh-shaped micro-electromagnet for the same current and electromagnet area. The measured results strongly agree with these conclusions resulted from the theoretical analysis. The results presented in this paper provide a solid and useful basis for the design of a micro-fluidic bio-molecule separation and detection system using magnetic fields and magnetic beads.
  • Micromagnetism and the Microstructure of Ferromagnetic Solids, H. Kronmüller et al. (2003)
    TitleMicromagnetism and the Microstructure of Ferromagnetic Solids
    AuthorsH. Kronmüller, M. Fähnle
    PublisherCambridge University Press
    AbstractThe main theme of this book is micromagnetism and microstructure as well as the analysis of the relations between characteristic properties of the hysteresis loop and microstructure. Also presented is an analysis of the role of microstructure in the fundamental magnetic properties (for example magnetorestriction or critical behaviour) of crystalline and amorphous alloys. The authors apply the theory of micromagnetism to all aspects of advanced magnetic materials including domain patterns and magnetization processes under the influence of defect structures. Coverage includes modern developments in computational micromagnetism and its application to spin structures of small particles and platelets. It will be of interest to researchers and graduate students in condensed matter, physics, electrical engineering and materials science, as well as to industrial researchers working in the electrotechnical and recording industry. * The first book to deal with the relations between magnetic properties and microstructure * Includes micromagnetism of advanced metallic materials * Describes computational micromagnetism of magnetization processes as well as the magnetic structures of small particles and thin films Contents 1. Introduction 2. Magnetic Gibbs free energy 3. Basic micromagnetic equilibrium conditions 4. Domain walls in crystalline and amorphous solids 5. Interaction of domain walls with defects 6. Coercivity of modern magnetic materials 7. Statistical theory of domain wall pinning 8. Law of approach to ferromagnetic saturation and high-field susceptibility 9. Microstructure and domain patterns 10. Magnetic after-effects in amorphous alloys 11. Magnetorestriction in amorphous and polycrystalline ferromagnets 12. Micromagnetic theory of phase transitions in spatially disordered spin systems 13. Computational micromagnetism of thin platelets and small particles 14. Computational micromagnetism of dynamic magnetization processes.
  • Magnetic Detection of Microstructural Change in Power Plant Steels , Victoria Anne Yardley (2003)
    TitleMagnetic Detection of Microstructural Change in Power Plant Steels
    AuthorVictoria Anne Yardley
    DateMay 2003
    AbstractPower plant components are expected to withstand service at high tem- perature and pressure for thirty years or more. One of the main failure mechanisms under these conditions is creep. The steel compositions and heat treatments for this application are chosen to confer microstructural sta- bility and creep resistance. Nevertheless, gradual microstructural changes, which eventually degrade the creep properties, occur during the long service life. Conservative design lives are used in power plant, and it is often found that components can be used safely beyond the original design life. How- ever, to benefit from this requires reliable monitoring methods. One such technique involves relating the microstructural state to measurable magnetic properties. Magnetic domain walls interact energetically with microstructural fea- tures such as grain boundaries, carbides and dislocations, and are ‘pinned’ in place at these sites until a sufficiently large field is applied to free them. When this occurs, the sudden change in magnetisation as the walls move can be detected as a voltage signal (Barkhausen noise). Previous work has suggested that grain boundaries and carbide particles in power plant steels act as pinning sites with characteristic strengths and strength distributions. In this study, the concept of pinning site strength distributions was used to develop a model for the variation of the Barkhausen noise signal with ap- plied field. This gave a good fit to published data. The modelling parameters characterising pinning site strengths showed good correlations with grain and carbide particle sizes. New Barkhausen noise data were obtained from tempered power plant steel samples for further model testing. The Orientation Imaging Microscopy (OIM) technique was used to investigate the grain orientations and grain boundary properties in the steel and their possible role in Barkhausen noise behaviour. The model again fitted the data well, and a clear relationship could be seen between the pinning strength parameter and the severity of tempering (as expressed by the Larson-Miller tempering parameter) to which the steel was subjected. The experimental results suggest that the Barkhausen noise characteris- tics of the steels investigated depend strongly on the strain at grain bound- aries. As tempering progresses and the grain boundary dislocation density falls, the pinning strength of the grain boundaries also decreases. A clear difference in Barkhausen noise response could be seen between a 2 1 Cr1Mo 4 traditional power-plant steel and an 11Cr1Mo steel designed for superior heat resistance. A study of an oxide dispersion strengthened ferrous alloy, in which the mi- crostructure undergoes dramatic coarsening on recrystallisation, was used to investigate further the effects of grain boundaries and particles on Barkhausen noise. The findings from these experiments supported the conclusion that grain boundary strain reduction gave large changes in the observed Barkhausen noise.
  • The physics of coercivity, Dominique Givord et al. (2003)
    TitleThe physics of coercivity
    AuthorsDominique Givord, Michel Rossignol, Vitoria M. T. S. Barthem
    PublicationJournal of Magnetism and Magnetic Materials
    DateMarch 2003
    AbstractIn hard magnets, coercivity is not a material intrinsic property. Magnetization reversal is constituted by a series of local processes, of which the first, termed as "true nucleation", takes place within a defect. An original analysis is proposed in this article which relates the coercive field Hc(T) to another experimental parameter, the activation volume. The obtained results exclude that coercivity is governed by true nucleation. Another process is necessarily involved before possible wall pinning in the bulk of the grains. It corresponds to the passage and expansion of the magnetic wall from the defect to the main hard phase. During passage/expansion, the wall energy increases progressively as the wall moves into regions with properties that approach those of the main hard phase and its surface area increases. At the same time, its behaviour tends to be governed by main phase properties. This scenario allows coercivity in hard magnets to be quantitatively interpreted.
  • On the electromagnetic force on a polarizable body, A. Engel et al. (2002)
    TitleOn the electromagnetic force on a polarizable body
    AuthorsA. Engel, R. Friedrichs
    PublicationAmerican Journal of Physics
    DateApril 2002
  • Microelectromagnets for the control of magnetic nanoparticles, C. S. Lee et al. (2001)
    TitleMicroelectromagnets for the control of magnetic nanoparticles
    AuthorsC. S. Lee, H. Lee, R. M. Westervelt
    PublicationApplied Physics Letters
    DateNovember 12, 2001
  • Layered Magnetic Structures: History, Highlights, Applications, Peter Grunberg (2001)
    TitleLayered Magnetic Structures: History, Highlights, Applications
    AuthorPeter Grunberg
    PublicationPhysics Today
    DateMay 00, 2001
    AbstractThe study of layered magnetic structures is one of the hottest topics in magnetism today, due largely to growing applications in magnetic sensors and in magnetic storage media like computer disks and random-access memories (see the article by L. M. Falicov in PHYSICS TODAY, October 1992, page 46, and the special issue of PHYSICS TODAY on magnetoelectronics, April 1995). Magnetic random-access memories (MRAMs) based on structures of magnetic metallic films interspersed with nonmagnetic metallic or insulating interlayers could be the next generation in magnetic-storage technology, replacing the semiconductor-based dynamic random-access memories (DRAMs) that are now the standard. Advantages of MRAMs include nonvolatility (they retain information when the computer is switched off), high storage density, and low energy consumption. Until the introduction of DRAMs in the 1970s, MRAM technology—using minute ferrite rings, or “core”—was dominant. Thin magnetic film was suggested as a replacement for core as early as 1955, and the first research results were presented in 1959, but problems with reliability of film-based MRAMs led instead to the adoption of DRAMs.
  • Shaped Ceramics with Tunable Magnetic Properties from Metal-Containing Polymers, Mark J. MacLachlan et al. (2000)
    TitleShaped Ceramics with Tunable Magnetic Properties from Metal-Containing Polymers
    AuthorsMark J. MacLachlan, Madlen Ginzburg, Neil Coombs, Thomas W. Coyle, Nandyala P. Raju, John E. Greedan, Geoffrey A. Ozin, Ian Manners
    DateFebruary 25, 2000
  • Anisotropy and phase transitions in atomically thin magnetic microstructures, A. Marty (2000)
    TitleAnisotropy and phase transitions in atomically thin magnetic microstructures
    AuthorA. Marty
    AbstractA recently developed technique allows the in situ fabrication of real two dimensional ferromagnetic particles. In this thesis a Scanning Kerr Microscope (SKEM) with a resolution of about 1mu is used to study the in-plane magnetization of such ultrathin particles on the micrometer size scale. The SKEM provides the possibility to measure the temperature dependent magnetization not only in zero magnetic field, but also in an applied external field. Magnetization loops M(H) can be collected at diferent spots on the sample. In addition, by scanning an interesting area we are able to map the magnetization in any external magnetic field along an in-plane direction. In the first part of this thesis a detailed study, of the magnetization of ultrathin Co particles evaporated on a Cu(100) single crystal is presented. The outstanding property is their single domain remanent state. They show square hysteresis loops along the easy magnetization axis with slightly varying fields Hc. The single domain state is stable and independent on the lateral extent of the structures, at least down to 1mu. Hysteresis loops are collected on particles of various lateral sizes and shapes to measure the switching behavior and the influence of their shape on their magnetization. We found that local changes in the substrate dominates over eventual size or shape dependence. No mutual interaction was observed for particles with a distance between each other down to 2mu. In the second part of this thesis the critical behaviour of in-plane magnetized Co/Cu(100) films and particles are investigated. The system exhibits a second-order phase transition from a ferromagnetic phase to a paramagnetic phase. In addition to the fourfold symmetry breaking field, a misfit in the Cu substrate causes a weak twofold anisotropy field. Both anisotropies scales differently with temperature and the transition is probably dominated by the uniaxial crystal field. However. the fourfold symmetry breaking cannot be neglected and causes non-universal behavior. Simultaneously collected M(H) curves parallel and perpendicular to the easy magnetization axis during phase transition reveal an anisotrupic behavior up to about 10 Kelvin above Tc and pronounced peaks in both susceptibilities at Tc. An analysis of the shape of the magnetization curves indicates that the fourfold symmetry breaking vanish slightly below T, while the twofold field persists. The relevant length at phase transition - the correlation length of the electron spins - develops to the maximum of about 1mu in our system. This is about the maximal particle size detectable with the SKEM. Finite size effects are therefore hard to observe. The values for the critical exponents beta, delta and gamma measured at 10x6mu2 and 4x4mu2 particles are slightly enhanced compared with the extended film values. In addition they exhibit a slightly different scaling function.
  • Atomically thin magnetic microstructures , C. Stamm (2000)
    TitleAtomically thin magnetic microstructures
    AuthorC. Stamm
    AbstractIn this thesis the magnetic properties of atomically thin microstructures are investigated. By drastically decreasing the size of a ferromagnet along one space dimension a two-dimensional particle results, which exhibits new magnetic behaviour. Domains in ferromagnetic bodies are the result of two competing interactions. The magnetostatic self-energy is reduced by the formation of magnetic domains with opposite magnetization. On the other hand exchange and anisotropy energy increase with each additional domain wall. The reason why in three-dimensional ferromagnets domains occur is that the agnetostatic energy is a volume energy, whereas the wall energy is a surface energy. Therefore, only small magnets are expected to be in a single-domain state. This is not necessarily true for two-dimensional magnets, where two different situations must be considered. In the first case, the magnetization is oriented parallel to the film plane. The physical systems investigated in this thesis are Co on a Cu(001) surface and Fe on a W(110) surface. The main result for in-plane magnetized structures is that they do not exhibit domains, irrespective of their size and shape. The smallest particle with rema- nent magnetization at room temperature was 130nm wide and 2 atomic layers thick. The shape anisotropy of stripes with in-plane aspect ratio R = 80 is negligible compared to the crystalline anisotropy. The mutual interaction between atomically thin magnets is too small to determine the magnetic configuration. In the second case, the magnetization stands perpendicular to the film plane, real- ized in this work by a few layers of Fe on Cu(001). Continuous films exhibit a striped domain configuration with local orientational order. When confining its lat- eral size on the micron scale a transition becomes visible, where magnetic particles below a critical size become single-domain. The phase transition of a perpendicular magnetized thin film to the paramagnetic state is found to happen in two steps, which is reminiscent of a two-dimensional melting process.
  • Magnetism of nanometer-scale iron particles arrays (invited), S. Wirth et al. (1999)
    TitleMagnetism of nanometer-scale iron particles arrays (invited)
    AuthorsS. Wirth, S. von Molnar, M. Field, D. D. Awschalom
    DateApril 15, 1999
    Proceedings TitleJ. Appl. Phys.
  • Permanent Magnets, J.M.D. Coey (1999)
    TitlePermanent Magnets
    AuthorJ.M.D. Coey
    PublicationWiley Encyclopedia of Electrical and Electronics Engineering
    AbstractThe sections in this article are: Magnetic Properties, Magnet Processing, Magnet Materials, Magnet Applications, Prospects
  • Ferromagnetic coercivity and applied field orientation, Brandon Edwards et al. (1995)
    TitleFerromagnetic coercivity and applied field orientation
    AuthorsBrandon Edwards, D. I. Paul
    PublicationJournal of Magnetism and Magnetic Materials
    DateJune 1995
    AbstractWe analyze the relationship between the coercive force of a ferromagnetic material and the angle of the applied magnetic field. The material is assumed to contain a ferromagnetic domain wall as well as a planar defect parallel to the wall and it is further assumed that the dominant mechanism determing the coercivity is that of pinning of the wall by the defect. Our formulation takes into account the spatial dependence of the direction of magnetization along the normal to the plane of the defect. Numerical solutions are obtained for the resulting nonlinear differential equations and analysis is done on the roles of the anisotropic, magnetostatic, and exchange energies in determining the behavior of the coercivity as the direction of the applied magnetic field is varied. Our results show that, in contradiction to previous thought, the inverse cosine of the applied field angle is not a good approximation to the coercivity dependence unless the coercivity is about two orders of magnitude smaller than the anisotropy field. Also, there exist ranges of parameter values for which the domain wall pinning coercivity decreases as the angle between the applied magnetic field and the anisotropy field increases - a behavior previously assumed to occur only when the coercivity is dominated by nucleation rather than pinning of domain walls. Thus, caution must be exercised when using the angular dependence of the applied field to determine the mechanism of magnetic reversal of a given material.
  • Comparison between various hysteresis models and experimental data , F. Ossart et al. (1990)
    TitleComparison between various hysteresis models and experimental data
    AuthorsF. Ossart, F. Ossart, G. Meunier
    PublicationMagnetics, IEEE Transactions on
    AbstractThe authors present a comparison between results predicted by four mathematical models of hysteresis and experimental data measured on a CoNiCr alloy for longitudinal recording. Two of those models are simple analytical formulas and can be used in a first approach to the phenomena, but are deficient in terms of modeling the behavior of minor loops. The other two models are more sophisticated. The first assumes a differential equation between B and H, while the other is derived from the Preisach model. The authors present results showing that, for the material studied, the last model gives the best fitting to experimental data
  • Angular dependence of coercivity in sintered magnets, D. Givord et al. (1988)
    TitleAngular dependence of coercivity in sintered magnets
    AuthorsD. Givord, P. Tenaud, T. Viadieu
    PublicationJournal of Magnetism and Magnetic Materials
    DateApril 2, 1988
    AbstractThe angular dependence of coercivity in sintered magnets is analysed within the framework of a model for magnetization reversal described previously. In systems where the coercive field is much weaker than the anisotropy field, magnetization reversal in each grain is determined by a 1/cos [theta] law, i.e. only the projection of the field along the magnetization is effective. The angular dependence of coercivity in magnets corresponds to such a law, convoluted with the angular distribution of grain orientations. In systems, where the coercive field is not negligible with respect to the anisotropy field, a coherent reversible rotation of the moments apart from their easy direction occurs prior to magnetization reversal and modifies the 1/cos [theta] law. Analysis of the observed behavior reveals then that, in the nucleus in which magnetization reversal is initiated, the anisotropy is not strongly reduced with respect to the bulk.
  • Theory of ferromagnetic hysteresis, D. C. Jiles et al. (1986)
    TitleTheory of ferromagnetic hysteresis
    AuthorsD. C. Jiles, D. L. Atherton
    PublicationJournal of Magnetism and Magnetic Materials
    DateSeptember 1986
    AbstractA mathematical model of the hysteresis mechanisms in ferromagnets is presented. This is based on existing ideas of domain wall motion including both bending and translation. The anhysteretic magnetization curve is derived using a mean field approach in which the magnetization of any domain is coupled to the magnetic field H and the bulk magnetization M. The anhysteretic emerges as the magnetization which would be achieved in the absence of domain wall pinning. Hysteresis is then included by considering the effects of pinning of magnetic domain walls on defect sites. This gives rise to a frictional force opposing the movement of domain walls. The impedance to motion is expressed via a single parameter k, leading to a simple model equation of state. This exhibits all of the main features of hysteresis such as the initial magnetization curve, saturation of magnetization, coercivity, remanence, and hysteresis loss.
  • Handbook of Magnetic Materials : Volume 1, E.P. Wohlfarth (1980)
    TitleHandbook of Magnetic Materials : Volume 1
    AuthorE.P. Wohlfarth
    PublisherNorth Holland
  • Ferromagnetism, R.M. Bozorth (1951)
    AuthorR.M. Bozorth
    PublisherVan Nostrand
    AbstractA reissue of a broadly recognized classic text, Ferromagnetism covers the basics of magnetics as well as in-depth coverage of magnetic materials. This timeless and invaluable reference also includes: * complete definitions of magnetic phenomena and theories * illustrations of magnetic materials * detailed explanations of basic magnetization and domain theory * practical use of many fundamental expressions * useful technical data on magnetic materials Ferromagnetism will provide a useful resource to any electrical engineer, physicist, researcher or designer, interested in the field of magnetics.