bluuebunny/crossref_metadata_2025 huggingface dataset:
“Decoding the Dots”: The ImageStream system (ISS) as a novel and powerful tool for flow cytometric analysis
Authors: Zuba-Surma Ewa , Kucia Magdalena , Ratajczak Mariusz
Published: December 2007

The aim of this article is to provide a brief review of the ImageStream system (ISS). The ISS technology was developed as a novel method for multiparameter cell analysis and subsequently as a supportive tool for flow cytometry (FC). ISS integrates the features of FC and fluorescent microscopy collecting images of acquired cells for offline digital image analysis. The article presents an overview of the main characteristics of ISS and a comparison between ISS, FC and the laser scanning cytometer (LSC). We reviewed ISS applications focusing on those involved in cellular phenotyping and provide our own experience with using ISS as a supportive tool to classical FC and demonstrate the compatibility between FC and ISS photometric analysis as well as the advantages of using ISS to confirm FC results.
DCC and TS protein expression in resected gastric cancer: A Hellenic Cooperative Oncology Group Study
Authors: Bamias Aristotle , Fountzilas George , Michael Michael , Konstantaras Christos , Vrettou Eleftheria , Eleftheriadis Efstathios , Papakostas Pavlos , Papadimitriou Konstantionos , Pavlidis Nicholas , Xiros Nikos , Bai Maria
Published: December 2007

There is a high risk of relapse after resection of gastric cancer. We studied the prognostic significance of the deleted colorectal cancer (DCC) gene and thymidylate synthase (TS) protein expression after resection of gastric cancer. Protein expression in the primary tumor of 146 patients with serosal and/or lymph node involvement was studied immunohistochemically by using anti-DCC and anti-TS monoclonal antibodies. DCC expression was found in 69.9%, while low TS staining intensity (0+,1+) and focal staining (<25% of tumor cells stained) were found in 44.6% and 33.8%, respectively. Overall survival (OS) was significantly longer in patients with DCC (p=0.014) negative tumors. TS expression was not an independent prognostic factor. Lack of DCC expression was associated with significantly longer cause-specific survival (CSS) (p=0.040) after curative resection. In conclusion, DCC expression is an independent prognostic factor in patients undergoing resection of gastric cancer while TS expression was not associated with the prognosis in our study.
Population-based cardiovascular risk factors in the elderly in Turkey: a cross-sectional survey
Authors: Ozkara Adem , Turgut Faruk , Kanbay Mehmet , Selcoki Yusuf , Akcay Ali
Published: December 2007

Hypertension, diabetes, hyperlipidaemia, obesity and smoking are known to be the most important modifiable risk factors for cardiovascular disease (CVD). Because the elderly population has been increasing globally, CVD may become a more important public health problem in the future. This report examines the prevalence of cardiovascular risk factors in the elderly in Ankara, Turkey. This was a cross-sectional survey and included a total of 2720 individuals living in the Ankara district. Trained research staff administered a standard questionnaire in the participants’ homes and worksites. The questionnaire collected information on clinical and demographic characteristics and a self-reported medical history, including past history of hypertension, diabetes, hyperlipidemia, coronary artery disease, coronary artery by-pass graft operation, and cerebrovascular accident. The mean age of the study participants was 69.5 ± 7.2 years. The study identified 1298 women (78.1%) and 753 men (71.2%) with hypertension, and the overall prevalence of hypertension was 75.4%. A total of 739 (27.2%) people had diabetes mellitus, and, of these people, 603 (81.6%) were hypertensive. A total of 1361 people had hyperlipidemia, and 1103 of these patients were also hypertensive. The overall prevalence of obesity was 27.2%. A total of 553 (20.3%) people were smokers. Our findings indicate that cardiovascular risk factors are very common in the elderly. To maximize risk reduction, physicians must take aggressive measures to decrease cardiovascular risk factors.
Coffee consumption and type 2 diabetes — An extensive review
Authors: Bidel Siamak , Hu Gang , Tuomilehto Jaakko
Published: December 2007

Coffee is a complex mixture of potentially active chemicals. It contains significant amounts of phenolic polymers, chlorogenic acid and also caffeine. Agricultural factors, roasting, blending, and brewing determine coffee’s chemical composition. Recent epidemiological studies suggest that habitual coffee consumption may help to prevent some chronic diseases including type 2 diabetes. Despite reports from the clinical trials of the effect of caffeine on decreasing insulin sensitivity, long-term prospective studies revealed that coffee may improve fasting glucose, glucose tolerance and insulin sensitivity as well. In the most recent publication habitual coffee drinkers have a lower total and cardiovascular mortality rate among diabetic subjects.
Comparative X-Ray study of galantamine and tacrine on the evacuatory function of rat gastrointestinal tract
Authors: Kristev Athanas , Sirakov Vladimir , Turiiski Valentin , Getova Damianka , Velkova Kichka
Published: December 2007

A The acetylcholinesterase inhibitors galantamine and tacrine are used to treat Alzheimer’s disease. However, these compounds also affect the gastrointestinal (GI) tract. Here, we compared and analyzed both the effects of galantamine-and tacrine on the evacuatory kinetics of the GI tract in rats. Rats were untreated (n=15) or treated with galantamine (one daily dose of 1 mg/kg per os for 21 days; n=17) or tacrine (one daily dose of 0.5 mg/kg per os for 21 days; n=13) and evacuatory kinetics were assessed using radiological methods. Galantamine initially slowed and then accelerated evacuation, which is characteristic of the majority of cholinesterase inhibitors and is a result of the endogenous acetylcholine accumulated in the GI tissues. In the tacrine-treated rats the contrast medium was kept in the stomach and cecum and its evacuation time was reliably increased. These results indicate that when administered for 20 days, galantamine and tacrine have different effects on motor and evacuatory function in the GI tract of rats, because at certain levels of the tract the tacrine-action is dominated by specific non-cholinergic and non-anticholinesterase mechanisms.
Theory of nonlinear Sagnac effect
Authors: Eliseev P.
Published: December 2007

A nonlinear wave interaction is considered as a technique to increase the rotation sensitivity of the ring laser. The gyroscopic scale factor K is calculated in an active laser gyro with a dispersive medium. K is in reverse proportion to the group index n* = n + vdn/dv of the medium. In a monolithically-integrated GaAs ring laser, the value K ∼5000 is obtainable (radius ∼1 cm) in a linear case. In the presence of a strong wave, the dynamic nonlinear anomalous dispersion can provide an increase of K by 10–100 times in the vicinity of critical points where n* passes zero. An expression of K is derived for the nonlinear Sagnac effect. The nonlinear dispersion is discussed in terms of “slow/fast” light.
Temporal electrical response of chiral smectic liquid crystal displays with V/W-shaped electrooptical characteristic
Authors: Pena J. , Pérez I. , Urruchi V. , Torres J. , Otón J.
Published: December 2007

Chiral smectic liquid crystal cells showing V-shaped electrooptical switching have been reported as one of the most promising technologies for high-end display applications. In this work, time-resolved electrical behaviour of these devices has been obtained through a set of systematic measurements. The electrical equivalent circuit has been derived, a number of simulations at different frequencies have been performed using commercial software for analogue circuits. Performance of this electrical model to account for time domain variations of switching currents in chiral smectic LC displays with V/W-shaped electrooptical response has been analyzed as well.
Multiband Hubbard Models and the Transition Metals
Authors: Stollhoff Gernot
Published: December 2007

Correlation computations on multiband Hubbard Hamiltonians are presented. It is shown why the proper degeneracy is of vital importance and that the atomic exchange interaction plays a particular role. The different methods are connected, and their results are discussed. Many experimental properties for the elemental solids can be explained by single closely related sets of parameters each. There is an exception,Tcof Fe. Here, a novel feature of longer‐range interactions enters. Connections are made to LSDA calculations, and their seeming successes and deficiencies are explained.
Quantum
M
onte
C
arlo Methods
Authors: Assaad Fakher F. , Troyer Matthias
Published: December 2007

We present a review of quantum Monte Carlo algorithms for the simulation of quantum magnets. A general introduction to Monte Carlo sampling is followed by an overview of local updates, cluster updates, and generalized ensemble techniques such as multicanonical and Wang‐Landau sampling for classical magnets. For quantum systems we present two complementary approaches: world‐line methods in (i) a path‐integral and (ii) a stochastic series expansion (SSE) representation, which are best suited for pure spin Hamiltonians. Determinental quantum Monte Carlo algorithms are the methods of choice for the simulation of fermionic Hamiltonians, such as the Hubbard model. An overview of the methods is followed by a selection of typical applications.
Phase Transitions and Finite Temperature Magnetism: Experiment and Analysis
Authors: Kaul Sharika Nandan
Published: December 2007

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

A 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

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

The 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

A 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.
Spin Waves: History and a Summary of Recent Developments
Authors: Mills D.L.
Published: December 2007

We review experimental and theoretical studies of spin waves in ferromagnets, with emphasis on the 3d ferromagnets along with films and multilayers formed from these materials.
Theory of Spin‐dependent Tunneling
Authors: Imamura Hiroshi , Maekawa Sadamichi
Published: December 2007

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

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

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

Micromagnetic 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

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

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

Magnetic 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

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

This 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

Polarized 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

X‐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

As 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

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

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

In 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

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.
Rare‐earth Intermetallics for Permanent Magnet Applications
Authors: Fidler Josef , Suess Dieter , Schrefl Thomas
Published: December 2007

Modern high‐performance permanent magnets are based on rare‐earth (RE) intermetallic compounds with excellent intrinsic magnetic properties as well as on optimized microstructures and alloy compositions. Outstanding hard magnetic properties such as energy density product and coercive field are obtained in binary and ternary RE (Sm, Nd, Pr) compounds with transition metals (TM = Co, Fe), in particular, based on RECo
5
and RE
2
Co
17
and RE
2
Fe
14
B. The complex microstructure considerably influences the magnetic reversal process. Intergranular phases change the coupling behavior between the hard magnetic grains. Nonmagnetic phases eliminate the direct exchange interaction and reduce the long‐range magnetostatic coupling. Both effects increase the coercive field in nucleation‐controlled magnets. The RE‐rich intergranular phase is necessary for the liquid phase sintering process, but deteriorates the corrosion stability and reduces the remanence. In order to improve coercive field, remanence and energy density, it is necessary to increase the volume fraction of the hard magnetic phase by reducing the amount of oxygen, nonmagnetic phases and pores, and to improve the degree of alignment of the hard grains. The difference in magnetic domain wall energy in precipitation hardened multiphase magnets determines the coercive field in domain wall pinning controlled magnets. The inhomogeneous magnetization behavior near the intergranular regions of nanocrystalline RE magnets, which is directly responsible for remanence and coercivity, is strongly influenced by the microstructural parameters. By using numerical micromagnetic simulations based on the finite element technique the correlation between microstructure and magnetic hysteresis properties can be quantitatively predicted, thus providing a powerful tool for the further development of optimized high‐performance Nd
2
Fe
14
B and Sm(Co,Cu)
5
/Sm
2
(Co,Fe)
17
‐type magnets.
Dilute Magnetic Oxides and Nitrides
Authors: Coey John Michael David , Rode Karsten
Published: December 2007

Recent reports on Curie temperatures well above room temperature for a number of dilute magnetic oxides and nitrides have triggered an intensive research on these compounds. Such materials are expected to play a key role in the development of electronics using the electron spin rather than its charge as information carrier. Furthermore, the fundamental origin of the magnetic interactions in these materials is of great interest as the
m
‐J paradigm seems unable to explain the observed magnetic behavior. In this paper, we outline the main magnetic interactions in dilute magnetic oxides and show that an alternative approach is needed to explain and understand the phenomena, and also review a selection of possible candidates for high Curie temperature dilute oxides.
Novel Nanoparticulate Magnetic Materials and Structures
Authors: Sellmyer David J. , Xu Yingfan , Sui Yucheng , Skomski Ralph
Published: December 2007

The article deals with free and embedded magnetic nanoparticles and with related magnetic structures, such as nanotubes and particulate thin films. The structures are relevant to modern technology, especially magnetic recording, where they have high potential for ultrahigh recording densities. After an introduction to magnetic recording, the focus is on relatively new preparation methods such as cluster deposition of magnetic metallic particles and synthesis in porous templates. The particles, tubes, and wires have dimensions between 1 nm and several 100 nm and exhibit a broad range of structural and magnetic properties. Present‐day recording media are longitudinal but soon there will be a transition to perpendicular recording media using very small grains for noise considerations and highly anisotropic materials to ensure thermal stability of the stored information. The considered materials range from transition‐metal elements and oxides, such as Fe, Co, and magnetite, to tetragonal FePt and rare‐earth transition‐metal (RE‐TM) alloys.
Crystallography and Chemistry of Perovskites
Authors: Johnsson Mats , Lemmens Peter
Published: December 2007

The perovskite family of oxides is probably the best studied family of oxides. Despite the simplicity of the original perovskite crystal structure related to the mineral perovskite CaTiO3, this family of compounds shows an enormous variety of structural modifications and variants. In the following text, we describe several examples of perovskites and discuss the implications of structural distortions and nonstoichiometry on their electronic and magnetic properties.
Chalcogenides and Pnictides
Authors: Fruchart Daniel , Wolfers Pierre
Published: December 2007

The first part of the chapter is dedicated to magnetic properties of metal phosphides and arsenides, mainly those with MX and M2X formulas. Their crystal structures are classified on the basis of the relative M–M and M–X bonding strength. Electronic origin instabilities of the d‐magnetism are underlined with reference to magnetoelastic, magnetic field, and pressure induced transitions, thus revealing high‐performing materials in terms of colossal magnetocaloric properties. In short, the second part reports on the knowledge of magnetic chalcogenides, from zinc‐blende spintronic materials up to recent studies on rare‐earth and uranium magnetic compounds.
Magnetic Carbon
Authors: Esquinazi Pablo
Published: December 2007

Landau–Lifshitz–Gilbert dynamics is investigated for uniformly magnetized particles subject to constant, pulsed, and circularly polarized applied fields. The Landau–Lifshitz–Gilbert equation is treated as a nonlinear dynamical system on the unit sphere. The equilibria and the phase portraits of this dynamical system, the nature of conservative (precessional) dynamics, and the nature of dissipation are discussed. Conservative Landau–Lifshitz dynamics is studied in detail and analytical expressions are derived for this dynamics in terms of elliptic functions. Then the problem of magnetization switching is studied in detail. Damping and precessional switchings of magnetization in spheroidal particles are discussed for rectangular field pulses, and expressions for critical fields and pulse durations are derived. The phenomenon of ringing, which occurs as the final stage of magnetization switching, is analytically studied using the averaging technique. The final section is devoted to the study of Landau–Lifshitz–Gilbert dynamics in uniformly magnetized particles with rotationally invariant properties, subject to a circularly polarized external field. By using geometric and topological considerations, exact uniform‐mode solutions of the full nonlinear dynamics are obtained for arbitrary values of the excitation conditions. The stability of these solutions is investigated and the conditions leading to periodic or quasiperiodic motions of the magnetization are established. Finally the problem of ferromagnetic resonance is treated using the developed analytical techniques.
Magnetocaloric Materials
Authors: Pecharsky Vitalij K. , Gschneidner Karl A.
Published: December 2007

Recent breakthroughs in design of advanced magnetocaloric materials signify that a paradigm shift in refrigeration, liquefaction, and freezing technologies is forthcoming. The concept of the magnetocaloric effect is introduced, the latest discoveries are reviewed and the current trends in engineering of novel magnetocaloric materials have been identified.
Advanced Magnetic Microwires
Authors: Vázquez Manuel
Published: December 2007

The most relevant aspects of magnetic amorphous microwires are collected in this chapter from production and processing methods to micromagnetic magnetization reversal processes, including selected technological applications finally paying particular attention to the actual search for novel microwire materials. After a first general review of the present state of the art in Section 1, the fabrication of amorphous and nanocrystalline microwires by rapid solidification techniques and subsequent processing is described in Section 2, including important characteristics such as mechanical stress distribution. Section 3 reviews the most interesting magnetic features of positive magnetostriction, Fe‐based microwires with bistable magnetic behavior such as: domain structure, magnetization reversal mechanism and its dynamics, magnetoelastic behavior, magnetostatic interactions in arrays of bistable microwires, and applications. Section 4 is devoted to the circular magnetization process and magnetoimpedance effect of nonmagnetostrictive microwires, the microwave properties, and their applications. Finally, Section 5 summarizes the latest results obtained in the search for novel microwires with new and/or optimized properties: nanocomposite and multilayer microwires.
Magnetic Ultrathin Films
Authors: Heinrich Bretislav , Cochran John Francis
Published: December 2007

The magnetic properties of ultrathin ferromagnetic films a few monolayers thick differ from the magnetic properties of the same material in bulk form because a large fraction of the atoms in such films are located either on the surfaces or within one monolayer of the surfaces. As a result, the magnetic properties of ultrathin films are very sensitive to surface roughness and to the proximity of foreign atoms at the interfaces with a substrate or with an overlayers film. The first part of this chapter provides an overview of three main methods for the preparation of ultrathin films: thermal deposition, laser pulse deposition, and magnetron sputtering. Emphasis is placed on techniques used to prepare high‐quality films having smooth surfaces and important examples are discussed in detail. The second part reviews magnetic anisotropies in ultrathin films: measuring techniques, the theory of magnetic anisotropies, and the effect of surface roughness on thin‐film anisotropies. The chapter closes with a guide to the literature on thin‐film magnetic anisotropy data for several interesting systems: Fe, Co, Ni films grown on various substrates; Fe films grown on GaAs crystals; Fe/Pt alloys grown on MgO; and bcc Ni films grown on GaAs(001).
Magneto‐optical Materials
Authors: Kleemann Wolfgang
Published: December 2007

After introducing the concepts of linear and nonlinear magneto‐optics in the visible spectral range, the flourishing field of X‐ray circular and linear dichroism is briefly discussed with pertinent examples. The experimental part starts with the basic idea of magneto‐optic ellipsometry and then focuses on the development of new experimental techniques like vector magneto‐optical Kerr effect (MOKE), diffracted MOKE, dynamic MOKE, nonlinear MOKE, and magneto‐optic X‐ray microscopy. Specified and timely material aspects are finally discussed under the topics magneto‐optical storage materials, magnetic semiconductors, antiferromagnets, and magnetophotonic crystals. It is stressed that the magneto‐optical probe is indispensable in the limits of very short times (femtomagnetism), that it plays a leading role in the development ofspintronics, and that nano‐ and microstructured magnetic materials have opened the new field ofmagnetophotonics.
Spintronic Biochips for Biomolecular Recognition
Authors: Freitas Paulo P. , Ferreira Hugo A.
Published: December 2007

The past few years have witnessed a continuously growing interest in the use of magnetic‐field sensors for biological applications. In particular, spintronic devices comprising magnetic‐field transducers such as anisotropic and giant magnetoresistive sensors, spin valves, magnetic tunnel junctions, and planar Hall effect sensors, are being developed in research laboratories and companies worldwide for biomolecular recognition detection. In these devices, the interaction between biomolecules, such as DNA–DNA hybridization, antibody–antigen recognition or general ligand‐receptor binding, is detected through the changes in resistance of a spintronic transducer that senses the stray field created by nano‐ or micrometer sized magnetic particles that label those interactions. Spintronic biochips hold the promise of becoming high‐performance and low‐cost tools that could revolutionize healthcare, the pharmaceutical industry, environmental analysis, and general biotechnological procedures. In this sense, systems are already being studied and developed for genetic disease diagnostics, microorganism identification, and biological warfare agent screening. In this chapter, an overview of magnetoresistive biochips will be given, together with recent developments on the field and some challenges for the future.
Ferroelectricity in Incommensurate Magnets
Authors: Harris A. Brooks , Lawes Gavin
Published: December 2007

We review the phenomenology of coupled magnetic and electric order parameters for systems in which ferroelectric and incommensurate magnetic order occur simultaneously. We first discuss the role that such materials might play in fabricating novel magnetoelectric devices. While the small polarization in these materials precludes their incorporation in many current ferroelectric devices, the strong coupling between magnetism and ferroelectricity in these systems offers entirely new functionalities. Next we briefly review the mean‐field description of ferroelectricity and modulated magnetic ordering. Since an understanding of the magnetic structure is so crucial, we present a simplified version of representation theory. In this theory, one considers the symmetry operations whichthat conserve the wave vector of the magnetic ordering to determine how crystal symmetry restricts the possible magnetic structures whichthat can appear at a continuous transition. Here we emphasize a relatively recent observation that even though inversion symmetry need not conserve the incommensurate wave vector, it does lead to important restrictions, usually on the phases of the complex spin Fourier transforms. We introduce magnetic order parameters to characterize the magnetic structure and display their symmetry properties. This enables us to analyze the symmetry of the interaction between the spontaneous polarization and the magnetic order parameters. We show how this formulation provides a phenomenological explanation for the observed phase transitions in Ni3V2O8and TbMnO3in which ferroelectric and magnetic order parameters simultaneously become nonzero at a single phase transition. In addition, this approach explains the fact that the spontaneous polarization only appears along a specific crystallographic direction. We analyze the symmetry of the strain dependence of the exchange tensor and show that it is consistent with the above macroscopic symmetry analysis. We devote a section to a discussion of possible directions of new experimental and theoretical research and we indicate how our understanding of these materials might influence the search for materials with larger magnetoelectric couplings at room temperature. Finally, we briefly review recent experiments on dynamical and optical properties whichthat appeared after initial preparation of this manuscript (August, 2005).