bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase Transitions and Finite Temperature Magnetism: Experiment and Analysis
Authors: Kaul Sharika Nandan 
Published: December 2007

Abstract
Magnetic excitations, prevailing in different temperature regimes that lie below the magnetic ordering temperature, and static critical phenomena near the thermally‐driven magnetic order–disorder phase transitions in spin systems in which the electrons responsible for magnetism are either localized or itinerant are reviewed from the experimental point of view. Besides bringing out clearly the importance of the energy and time scales governing various physical processes connected with the finite temperature magnetism and phase transitions in such systems, a brief account of the relevant theoretical background and crucial steps in the data analyses is given so as to prepare the ground for a meaningful comparison between theory and experiment. Such a comparison, in turn, is shown to provide improved understanding of the nature and origin of magnetic excitations and critical phenomena in localized‐spin and itinerant‐electron systems. In addition, this review highlights both the power as well as the limitations of the experimental techniques employed in the literature to study magnetic excitations and deals extensively with the magnon‐to‐fracton crossover in systems with localized spins and crossovers between different critical regimes in isotropic spin systems with long‐range interactions or spin systems in which long‐range interactions occur in association with magnetic anisotropy.
Magnetostriction and Magnetoelasticity Theory: A Modern View
Authors: del Moral A. 
Published: December 2007

AbstractA current modern status of magnetostriction (MS), magnetoelastic (MEL) coupling and magnetoelasticity (ME) theory and models (spin waves, band MS Hubbard forced MS, spin fluctuations, weak ferromagnets,ab initio, MEL parameters calculation, strongly correlated systems) is presented, particularly thestandard theory for magnetostriction(i.e., built up of MEL Hamiltonians and temperature dependence of crystal field (CEF) and two‐ion MSs). Chapter is preceeded by the phenomenological theory of MS, based on symmetry and thermodynamics. Nuclear to the MS and ME presentations is the study of MEL coupling (of CEF single‐ion and exchange two‐ion origins), including rotational strains and central rotational invariance theorem. Magnetostriction in magnetic insulators and itinerant magnets is considered, either magnetically ordered or magnetically/structurally disordered. Magnetoelasticity dynamics and sound wave propagation (elastic constant MEL contribution) are considered, particularly magnetoacoustic waves and magnetic birefringence and Faraday rotation. Chapter ends with magnetostriction in surfaces, films and superlattices.
Disordered and Frustrated Spin Systems
Authors: Binder Kurt , Young A. Peter 
Published: December 2007

Abstract

A brief review on the effects of quenched disorder on magnetic ordering is given. This disorder can be due to dilution of a ferro‐ or antiferromagnetic crystal with nonmagnetic atoms, or due to noncrystallinity (amorphous magnetic systems). This disorder in the positions of the magnetic atoms leads to disorder in the exchange interactions between spins. If the disorder is sufficiently weak, the critical temperature of magnetic ordering is somewhat decreased, and the critical behavior may change, but the
nature
of ordering is maintained. However, if the disorder is sufficiently strong, magnetic long‐range order may disappear altogether at a percolation threshold, or a new type of order may appear, the ‘spin glass’, in which spins freeze in random directions because of random competition between ferro‐ and antiferromagnetic interactions. In this context, we also mention magnetic systems with ‘frustration’ of their exchange interactions but without disorder. Finally, another important class of phenomena occurs for systems with ‘random fields’, an example of which is provided by diluted antiferromagnets in a uniform field.
Magnetism of Low‐dimensional Metallic Structures
Authors: Enders Axel , Gambardella Pietro , Kern Klaus 
Published: December 2007

AbstractThe chapter “Magnetism of low‐dimensional metallic structures” reviews experiments on the magnetism of surface‐supported low‐dimensional structures of 3d metals. Controlling the static and dynamic magnetic behavior of both individual impurities and supported nanostructures on nonmagnetic surfaces represents a fundamental challenge as well as a prerequisite to design magnetic storage and logic devices of novel conception. We describe the governing principles of self‐organized growth of metallic nanostructures at surfaces and outline approaches to drive and steer self‐assembly processes. The controlled assembly of metal nanostructures on crystalline surfaces combined with scanning probe measurements and synchrotron radiation spectroscopy allows us to track the evolution of the magnetic properties from single atoms to finite‐sized particles, atomic chains, and two‐dimensional layers, highlighting the significance of size, coordination, and interface effects at the atomic scale. As examples, we report on the giant magnetic anisotropy and unquenched orbital moments observed in nanoparticles, unusual oscillations of the easy axis of magnetization in atomic chains of variable thickness, and metastable ferromagnetic order in one‐dimension. We discuss the important role played by interactions with a nonmagnetic substrate and point out approaches to control and tune magnetism in nanoscale structures by taking advantage of coordination and hybridization effects.
X‐ray and Neutron Scattering by Magnetic Materials
Authors: Lovesey S.W. , Tanaka Y. 
Published: December 2007

AbstractA brief survey of theory designed to interpret observations on magnetic materials using neutron and X‐ray scattering techniques is presented. Emphasis is placed on X‐ray scattering because it remains an emerging subject and neutron scattering is thoroughly reviewed in several places.
Theory of Spin‐dependent Tunneling
Authors: Imamura Hiroshi , Maekawa Sadamichi 
Published: December 2007

Abstract
In this chapter, we provide a review of the theories of spin‐dependent tunneling in magnetic tunnel junctions. The chapter is organized as follows. The tunneling Hamiltonian model is described in Section 2. We explain the basic ideas for dealing with the electron tunneling and derive the expression of the tunneling current and TMR. We also show some recent advances in the theory of spin‐dependent tunneling in a Coulomb blockade regime. In Section 3, we provide a brief review of the free‐electron model and show that the TMR is not a monotonic function of the barrier height. In Section 4, we review the theory of spin‐dependent tunneling based on the tight‐binding model and its application to various magnetic tunnel junctions. The first‐principles model and its applications to the epitaxial magnetic tunnel junctions with MgO barriers are described in Section 5.
The
B
erry Phase in Magnetism and the Anomalous Hall Effect
Authors: Bruno Patrick 
Published: December 2007

Abstract
The concept of geometrical phase, introduced by Berry in 1984, has proved to be an extremely fruitful unifying concept in quantum mechanics. In this Chapter, an elementary introduction to the Berry phase is presented, with special emphasis to its role in modern magnetism. In particular, the problem of the anomalous Hall effect, which benefited consederably from new light shed by the Berry phase concept, is discussed in detail.
Numerical Micromagnetics: Finite Difference Methods
Authors: Miltat Jacques E. , Donahue Michael J. 
Published: December 2007

Abstract
Micromagnetics is based on the one hand on a continuum approximation of exchange interactions, including boundary conditions, on the other hand on Maxwell equations in the nonpropagative (static) limit for the evaluation of the demagnetizing field. The micromagnetic energy is most often restricted to the sum of the exchange, demagnetizing or self‐magnetostatic, Zeeman, and anisotropy energies. When supplemented with a time evolution equation, including field induced magnetization precession, damping and possibly additional torque sources, micromagnetics allows for a precise description of magnetization distributions within finite bodies both in space and time. Analytical solutions are, however, rarely available. Numerical micromagnetics enables the exploration of complexity in small size magnetic bodies. Finite difference methods are here applied to numerical micromagnetics in two variants for the description of both exchange interactions/boundary conditions and demagnetizing field evaluation. Accuracy in the time domain is also discussed and a simple tool provided in order to monitor time integration accuracy. A specific example involving large angle precession, domain wall motion as well as vortex/antivortex creation and annihilation allows for a fine comparison between two discretization schemes with as a net result, the necessity for mesh sizes well below the exchange length in order to reach adequate convergence.
Numerical Methods in Micromagnetics (Finite Element Method)
Authors: Schrefl Thomas , Hrkac Gino , Bance Simon , Suess Dieter , Ertl Otmar , Fidler Josef 
Published: December 2007

AbstractMicromagnetic simulations provide guidelines for the development of composite magnetic materials and magnetic devices. The granular structure of a material and the magnetic interactions between the different magnetic parts of a device can be easily taken into account by the finite element method and the boundary element method, respectively. The finite element equations are derived for the calculation of the magnetostatic field. Similarly, it is shown how the total energy of a magnetic system can be computed by matrix‐vector operations. Efficient methods for calculating equilibrium magnetic states and the simulation of the dynamic response of a magnetic material to a time varying external field are discussed. Numerical schemes for the simulation of magnetization dynamics in systems involving moving parts are introduced. The numerical methods are demonstrated by showing results of perpendicular magnetic recording simulation on composite media.
Current Induced Domain‐wall Motion in Magnetic Nanowires
Authors: Thomas Luc , Parkin Stuart 
Published: December 2007

Abstract
Recent research on current‐induced domain‐wall motion in magnetic nanowires is reviewed. The first part of the article is devoted to theoretical models and micromagnetic simulations. We first describe the magnetic structure of head‐to‐head domain walls, and then discuss theories of their interaction with spin‐polarized current. The role of both adiabatic and nonadiabatic spin‐transfer torques is discussed in the framework of an analytical one‐dimensional model and micromagnetic simulations. The second part of the article reviews recent experimental studies. Both field‐driven and current‐driven excitation and manipulation of domain walls is discussed.
Guided Spin Waves
Authors: Hertel Riccardo 
Published: December 2007

Abstract
Patterned ferromagnetic magnetic thin films of submicron size can serve as waveguides for spin waves. This chapter emphasizes the interaction of spin waves with magnetic domain walls for the case of propagating spin waves in thin magnetic strips. The study is based on micromagnetic simulations. It is shown that by manipulating the phase of propagating spin waves and by combining magnetic strips in patterned thin‐film elements, spin waves can be used for logical operations.
A typical device is a magnetic interferometer where spin waves split along different paths and then are recombined to produce constructive or destructive interference, depending on the magnetic structures of the separate paths. Simulations show that 360° domain walls can produce phase shifts of 180°. The calculations are carried out using the dynamic Landau–Lifshitz–Gilbert integro‐differential equations of micromagnetism with finite elements. The finite‐element method greatly reduces the computational artifacts that can arise from the discretization, especially in this case where patterned elements with curved surfaces are modeled. Results are shown for stripes, tuning forks, and interferometer patterns as an introduction to the basic elements of spin‐wave logics. The phase shifts of the spin waves are of fundamental interest and provide an instructive example of the concept of Berry phases in magnetism.
Micromagnetism–Microstructure Relations and the Hysteresis Loop
Authors: Goll Dagmar 
Published: December 2007

AbstractMagnetic materials are widely used in many (modern) application fields ranging from electrical engineering, car industry and energy technique to sensor systems, high‐density recording and applications in medicine and biology. For a technological progress in these fields and for an application‐oriented magnet design the characteristic magnetic properties of the hysteresis loop are of great importance. Their steady improvement brings about in particular a continuous miniaturization of magnetic devices (hard magnetic materials) and a continuous reduction of energy losses during energy transmission (soft magnetic materials) leading to innovations in many new application fields and consequently to a rapid growth of the worldwide market.Modern high‐quality magnets are based on both optimized microstructures (including defect structures) and compounds with outstanding intrinsic material parameters. Optimized microstructures are composed of amorphous regions and/or ensembles of small magnetic grains with length scales varying from nm to cm. These extrinsic magnetic properties can be controlled by the choice of the alloy composition from the phase diagram (including small amounts of additives) and by the processing route as e.g. sintering, rapid quenching, sputtering or molecular beam epitaxy (including thermal and mechanical treatments). The detailed analysis of microstructure‐magnetic property relationships by means of different high‐resolution electron microscopy techniques and magnetic hysteresis loop measurements in combination with the theory of micromagnetism allows a quantitative interpretation of magnetization processes responsible for magnetic softening/hardening. This provides general rules for a successful specific tailoring of optimized characteristic magnetic properties of the hysteresis loop in the whole ferromagnetic (or ferrimagnetic) temperature range.
Modelling of Nonlinear Behaviour and Hysteresis in Magnetic Materials
Authors: Jiles David C. , Melikhov Yevgen 
Published: December 2007

Abstract
Magnetic hysteresis models such as Landau–Lifshitz–Gilbert, Stoner–Wohlfarth, Globus, Preisach, and Jiles–Atherton are described. Discussion focuses on the underlying basic concepts. The various models span a range of length scales from the atomistic scale to the continuum, and need to be applied with careful consideration of the appropriate length scale of interest in any particular case. In general, all of these models are approximations to complicated systems with many different and competing interactions on different length scales. Therefore, depending on the relative importance of the interactions and the length scale of interest, different models are appropriate to different situations.
Domain States Determined by Neutron Refraction and Scattering
Authors: Hoffmann Axel , Felcher Gian P. 
Published: December 2007

AbstractThis chapter discusses various neutron refraction and scattering techniques, which are used to investigate magnetic domain states in ferromagnets and antiferromagnets. Besides giving a brief introduction into the various possible techniques, there are also examples of the current relevant science issues presented, which lend themselves to neutron measurement investigations.
Polarized Neutron Reflectivity and Scattering from Magnetic Nanostructures and Spintronic Materials
Authors: Zabel Hartmut , Theis‐Bröhl Katharina , Toperverg Boris P. 
Published: December 2007

AbstractPolarized neutron reflectivity and scattering has established itself as one of the most important experimental methods for the analysis of magnetic nanostructures and spintronic materials. With this method, seminal contributions have been made to the physics of thin magnetic films, interfaces, and superlattices, including collinear and noncollinear exchange coupling. Another rich area is the exchange coupling phenomena between ferromagnetic and antiferromagnetic layers. Presently neutron scattering from laterally patterned magnetic arrays has become very active for the understanding of domain structures, domain reversals, and correlation effects. Established more than 25 years ago, polarized neutron reflectivity was focused mainly on the specularly reflected intensity. With the advent of area detectors and efficient wide‐angle spin analyzers, the off‐specular diffuse scattering could be analyzed, contributing to a more complete picture of the physics of magnetic nanostructures and patterned arrays. In this review a basic introduction into the fundamentals of polarized neutron reflectivity is provided, including specular and off‐specular scattering. For the description of the off‐specular part, the distorted wave Born approximation has rigorously been applied and features missed in the simpler Born approximation are pointed out. The methods are illustrated by a number of examples from research into magnetic thin films, spin valves, magnetic multilayers, exchange bias systems, spintronic materials, and periodic magnetic arrays of islands and stripes.
Synchrotron Radiation Techniques Based onX‐rayMagnetic Circular Dichroism
Authors: Schütz Gisela , Goering Eberhard , Stoll Hermann 
Published: December 2007

AbstractX‐ray magnetic circular dichroism (XMCD) results from the dependence of the absorption cross section on the magnetization of the target. The use of highly intense, circular‐polarized synchrotron X‐ray sources close to an absorption edge energy allows an element‐specific and quantitative determination of local magnetic spin and orbital moments. If the energy is tuned to the circular dichroic active absorption edges, most of the X‐ray spectroscopic scattering and imaging techniques can be extended to their magnetic counterpart, which provides new insights into magnetic, electronic, and geometric structures and phenomena.
Lorentz Microscopy of Thin‐film Systems
Authors: Zweck Josef , Uhlig Thomas 
Published: December 2007

AbstractAs there is growing interest in laterally confined, small magnetic particles in the sub‐µm and sub‐100 nm regime, researchers look for techniques which are capable to quantitatively measure magnetic properties in this range. Electron microscopy offers a technique which combines very high lateral resolution down to presently 5 nm and at the same time high sensitivity to the specimen's magnetic induction. However, to understand fully the present and future possibilities of ‘Lorentz’ electron microscopy, a brief introduction to the main techniques, such as Fresnel and Foucault imaging, differential phase contrast and electron holography has to be given. This more technical section is followed by various examples of what can be achieved today–measurement of hysteresis loops of individual particles, observation of magnetic configuration in the deep sub‐µm regime, observation of magnetic stray fields–and what will probably be possible in near future.
Scanning Electron Microscopy with Polarisation Analysis
Authors: Oepen Hans Peter , Frömter Robert 
Published: December 2007

Abstract
The scanning electron microscope with polarization analysis (SEMPA or spin‐SEM) is a powerful tool to investigate the magnetic structure of ferromagnetic surfaces with high spatial resolution. In the article the spin polarized secondary electron emission is described and discussed as the contrast generating process that is utilized in SEMPA. Taking the secondary electron emission from itinerant ferromagnets as starting point, the properties and best case performance of spin‐SEM are derived. The consequences of these properties for the realization of such a microscope and the polarization analyzer, as well as the resulting strengths and weaknesses of the technique are discussed. The best case performance is compared to the actual performance of a newly designed microscope. Several examples for the application of spin‐SEM are presented; e.g. the study of the spin‐reorientation transition in ultrathin films and interlayer exchange coupling. It is shown how a decoration technique can be used to analyze ferromagnets where the surface is non‐magnetic due to contamination or capping by a protective layer. Finally, the influence of sample morphology on the polarization detection and details of the analysis of the vectorial polarization measurement are comprehensively discussed.
Growth of Magnetic Materials using Molecular Beam Epitaxy
Authors: Eckstein James N. 
Published: December 2007

Abstract
A wide variety of magnetic materials and devices have been prepared by molecular beam epitaxy (MBE). The accurate growth of multilayers and superlattices involving magnetic phases has made possible experiments that have uncovered how magnetic order propagates at interfaces. This has uncovered new physical effects and made possible the study of new devices assembled with atomic accuracy.
Crystal Growth of Magnetic Materials
Authors: Behr Günter , Löser Wolfgang 
Published: December 2007

AbstractIn this chapter, the various methods for crystal growth of magnetic materials are summarized and principles of choosing the appropriate growth method, which depends on phase diagram features of the alloy system, the required size, physical, and chemical perfection of single crystalline samples, are briefly discussed. The crystal growth of the following classes of materials is considered: soft magnetic pure metals and alloys, highly anisotropic compounds for high‐density magnetic recording media, rare earth–transition metal compounds for high‐performance permanent magnets, high‐magnetostrictive intermetallic compounds and ferromagnetic shape memory alloys for magnetomechanical applications, magnetocaloric materials, selected intermetallic compounds for spintronics, multiferroic materials, and some other less‐common magnetic compounds.
Amorphous Alloys
Authors: Davies Hywel A. , Gibbs Michael R.J. 
Published: December 2007

Abstract
An overview is presented of the principal aspects of metallic glasses that relate to their applications in ferromagnetic devices. Following an outline of the historical background, the topics covered include the following: (i) the main characteristics of glassy alloys, with particular emphasis on ferromagnetic variants; (ii) structure, formation, and thermal stability; (iii) mechanical properties and thermal embrittlement; (iv) the influence of composition on saturation magnetic moment and on Curie temperature; (v) the compositional and thermal requirements for glassy phase formation and the processes for producing the materials in ribbon form, together with a summary of the techniques for synthesizing alloy glass powders; (vi) induced magnetic anisotropy and magnetostriction, including the effects of Fe:Ni:Co ratio on saturation magnetostriction; (vii) permeability, magnetic losses, and transformer applications; and (viii) the use of metallic glasses in magnetic sensors.