bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Flow to a Well Produced at a Constant Pressure in a Fractured Reservoir
Authors: Ozkan E. , Ohaeri U. , Raghavan R.
Published: December 2007

The objective of this theoretical study is to delineate the characteristics of a well producing at a constant pressure in a naturally fractured reservoir. We consider flow to a well located at the center of a closed circular reservoir. New solutions not documented previously are presented. Five flow regimes are identified and information that can be extracted from each regime is documented. Methods to determine formation parameters and to predict well deliverability are discussed.
Wellbore Effects in the Analysis of Two-Phase Geothermal Well Tests
Authors: Miller Constance W. , Benson Sally M. , O'Sullivan Michael J. , Pruess Karsten
Published: December 2007

A method of designing and analyzing pressure transient well tests of two-phase (steam/water) reservoirs is given. Wellbore storage is taken into account, and the duration of it is estimated. It is shown that the wellbore flow can dominate the downhole pressure signal completely such that large changes in the downhole pressure that might be expected because of changes in kinematic mobility are not seen. Changes in the flowing enthalpy from the reservoir can interact with the wellbore flow so that a temporary plateau in the downhole transient curve is measured. Application of graphical and nongraphical methods to determine reservoir parameters from drawdown tests is demonstrated.
Flow Characteristics of Surfactant Solutions in Porous Media and Their Role in Permeability Modification
Authors: Kalpakci B. , Klaus E. E. , Duda J. L. , Nagarajan R.
Published: December 2007

This paper presents results of a study on flow properties of surfactant solutions in porous media, using the Penn State porous media viscometer. The effects of permeability, shear rate, and surface characteristics of porous media on the flow of oil- and water-external microemulsions, as well as surfactant solutions with lamellar structures, are examined. Untreated Bradford and Berea sandstones, oil- and water-wet treated sandstones, and filter papers are used as porous media.

The study shows that the effective viscosity of the surfactant solution (as measured in porous media), on the basis of initial permeabilities, is greater than the bulk viscosity (as measured by conventional viscometers). This increase is small for Newtonian surfactant solutions but is quite substantial for non-Newtonian surfactant solutions. The difference between bulk and effective viscosities of Newtonian surfactant solutions is eliminated when the effective viscosity is determined on the basis of the final permeability of the porous medium to calibration solution. This indicates that the permeability of the porous medium during flow of these Newtonian surfactant solutions is equal to that during flow of postcalibration solutions. In contrast, in the case of the non-Newtonian surfactant solution with lamellar structures, the effective viscosity based on the final permeability remains higher than the bulk viscosity of the solution. Plausible explanations for the lower permeability during surfactant flow compared with the final permeability, in this case, are discussed.

It is found that the flow of surfactant solutions causes a permanent decrease in the permeability of the porous medium. Initial permeability is not restored even by thorough flushing of the porous medium with surfactant-free brine solution. Residual permeability reductions of 2 to 51% are observed. The residual permeability reduction increases with decreasing initial permeability. The residual permeability reduction is relatively insensitive to the type of surfactant solution. However, it depends on surface characteristics of the porous medium and decreases in this order: untreated ≫ fired > oil-wet treated.
Use of Perspective Plots To Aid in Determining Factors Affecting Interfacial Tensions Between Surfactant Solutions and Crude Oil
Authors: Kellerhals G. E. , Chiou C. S.
Published: December 2007

In surfactant flooding, low interfacial tensions (IFT's) are required for recovery of additional significant quantities of crude oil from a reservoir rock. This paper indicates the usefulness of perspective plots to facilitate comparison of sets of IFT data. Such perspective plots simplify the process of screening various surfactant systems for enhanced oil recovery.
Fracture Evaluation With Pressure Transient Testing in Low-Permeability Gas Reservoirs
Authors: Lee W.J. , Holditch S.A.
Published: December 2007

This paper presents theoretical and practical aspects of methods used to determine formation permeability, fracture length, and fracture conductivity permeability, fracture length, and fracture conductivity in low-permeability, hydraulically fractured gas reservoirs. Methods examined include Horner analysis, linear flow analysis, type curves, and finite-difference reservoir simulators.

Introduction

The purpose of this paper is to summarize the theoretical background of methods that we have attempted to use to determine formation permeability, fracture length, and fracture conductivity permeability, fracture length, and fracture conductivity in low-permeability, hydraulically fractured gas reservoirs. This summary is intended to emphasize the major strengths and weaknesses of the methods studied. These characteristics have not always been emphasized in the original literature and, in some cases, have remained obscure to the practicing engineer. The paper also includes examples from 13 wells in which postfracture-treatment pressure buildup surveys have been analyzed in detail.

Test analysis methods discussed in the paper include (1) a method applicable only after a pseudoradial flow pattern is developed in the pseudoradial flow pattern is developed in the reservoir, (2) a method applicable when linear flow dominates in the reservoir, (3) published type curves, with emphasis on those that include finite- conductivity fractures, (4) a modification of linear- flow techniques useful for finite-conductivity fractures, and (5) use of finite-difference reservoir simulators in a history-matching mode.

Pseudoradial Flow Pseudoradial Flow Russell and Truitt pioneered application of methods based on the assumption of pseudoradial flow in a fractured reservoir for determination of formation permeability and fracture length. A working permeability and fracture length. A working definition of pseudoradial flow is that sufficient time has elapsed in a buildup or drawdown test so that bottomhole pressure (BHP) varies linearly with the logarithm of flow time (drawdown) or the Horner time group (tp + delta t)/ delta t (buildup), as expected for radial flow in an unfractured reservoir.

In an infinite-acting (unbounded) reservoir, the analysis technique is based on the use of skin factor, s, which can be calculated from

(1)

and the observation that, for infinitely conductive vertical fractures,

(2)

Eqs. 1 and 2 can be combined to avoid the intermediate step of calculating s:

(3)

In principle, we can plot buildup test data on a conventional Horner graph, determine the slope m, and thus estimate formation permeability (k = 162.6 qgBga mu a/mh) and determine fracture half-length, Lf from Eq. 3 (see Fig. 1).

JPT

P. 1776
Refractory shoulder dystocia in term macrosomic newborn with verified complete meningoencephalomyelocele
Authors: Habek Dubravko , Horvat Gordana , Kulaš Tomislav , Janiška Ivanka , Stanojević Milan , Bauman Renato , Hafner Tomislav
Published: December 2007

The authors presented the birth course, in a primiparous woman with complicated, refractory, high shoulder dystocia, of a macrosomic term-born malformed child (4400/54) with complete occipital meningoencephalomyelocele and microcephaly. After head delivery, high shoulder dystocia occurred that could not be resolved with neither the McRoberts or Resnik maneuver nor with the Woods and Barnum maneuvers, despite recurred tries. Only on third attempt with the Barnum maneuver was the posterior arm released with hand traction, followed by the whole body of the macrosomic baby. The child was transferred to the Neurosurgery department where operative correction was performed, and after the intervention the child died because of respiratory insufficiency. Due to the strict parental decision on pregnancy continuation and prohibition of any obstetric interventions during delivery, unborn child and parturient, as well as the obstetric team, were put into high professional, forensic and ethical risk.
Swept Under the Rug? A Historiography of Gender and Black Colleges
Authors: Gasman Marybeth
Published: December 2007

This historiography of gender and black colleges uncovers the omission of women and gender relations. It uses an integrative framework, conceptualized by Evelyn Nakano Glenn, that considers race and gender as mutually interconnected, revealing different results than might be seen by considering these issues independently. The article is significant for historians and non-historians alike and has implications for educational policy and practice in the current day.
Perils of Accommodation: The Case of Joseph W. Holley
Authors: O’Brien Thomas V.
Published: December 2007

This study examines accommodationism, a tactic of racial uplift used by black school founders and teachers in the Jim Crow South. For founders, accommodationism was a dangerous process of collaboration, resistance, and compromise. The subject under study is Joseph Winthrop Holley. Born in South Carolina, Holley studied in the North at Phillips Academy and Lincoln University. Despite a liberal education, Holley returned to the South and founded a Bible and industrial school. Holley was the most conservative founder of his day. His life and work take us beyond the Washington–Du Bois paradigm and help to clarify the work and meaning of accommodationism. The study also evaluates the degree to which conservative forms of schooling became a means for social control.
Dynamical Mean‐Field Theory of Itinerant Electron Magnetism
Authors: Lichtenstein Alexander I. , Katsnelson Mikhail I.
Published: December 2007

A novel spectral density functional approach to electronic correlations and magnetism of crystals based on realistic electronic structure calculations is reviewed. In its simplest form, it is a combination of the density functional theory in the ‘local density approximation’ with dynamical mean‐field theory approaches. Using the numerically exact solution of an effective multi‐orbital quantum‐impurity problem, a successful description of the electronic structure and finite‐temperature magnetism of transition metals has been obtained. We discuss correlation effects in iron and nickel, as well as in an artificially prepared layered structure of manganese. A general scheme for calculation of effective exchange interactions in the strongly interacting magnetic systems is presented. Correlation effects in half‐metallic ferromagnets resulting in the formation of nonquasiparticle states within the minority (or majority) spin gap are also discussed.
Heavy Fermions: Electrons at the Edge of Magnetism
Authors: Coleman Piers
Published: December 2007

An introduction to the physics of heavy‐fermion compounds is presented, highlighting the conceptual developments and emphasizing the mysteries and open questions that persist in this active field of research.
Orbital Physics in Transition Metal Oxides: Magnetism and Optics
Authors: Horsch Peter
Published: December 2007

Orbital degeneracy and strong correlations in transition‐metal oxides generate spins and orbitals as low‐energy degrees of freedom. Their interplay with both real‐charge motion and virtual‐charge excitations lead to a fascinating richness of spin–charge–orbital‐ordered phases in transition‐metal oxides, to striking phenomena like the colossal magnetoresistance in manganites, the switching of charge‐ordered phases into metallic phases by applied magnetic field, and many other fascinating effects. Central topics of this review are the spin‐orbital superexchange models which provide a concise description of spin and orbital order, effective spin interactions, spin waves, and orbiton excitations in doped and undoped Mott insulators. Particular emphasis is put on recent developments of spin‐orbital superexchange models, the relation of magnetism and optical spectral weights and their temperature dependence, t
2g
systems with strong composite spin‐orbital fluctuations, the concepts of orbital liquid, orbital polarons, and the colossal magnetoresistance.
Quantum Phase Transitions
Authors: Sachdev Subir
Published: December 2007

Thermal fluctuations induced by increasing temperature can change the state of matter, for example, when water boils to steam. It also is possible to change the state of matter at absolute zero temperature by quantum fluctuations demanded by Heisenberg's uncertainty principle. In this case, the quantumphase transition from one state to another is provided by adjusting a tuning parameter other than temperature. A few characteristic examples of quantumphase transitions are reviewed, and their consequences for finite temperature experiments are discussed.
Electron Theory of Finite Temperature Magnetism
Authors: Kübler Jürgen
Published: December 2007

The theory of finite‐temperature magnetism of metals is formulated within the local spin‐density‐functional approximation. Orientational fluctuations of the local magnetization are at the basis of the thermodynamic theory, for which the excitations are obtained from the total‐energy differences of noncollinear spin configurations, modeled either in real or reciprocal space. The limit of weakly ferromagnetic metals (e.g., ZrZn
2
, Ni
3
Al, and MnSi) is formulated by including dissipation effects in the spin‐fluctuation theory. Moriya's unified theory is used to derive formulas for the Curie temperature in the spherical approximation which are used together with the mean‐field approximation and reported Monte Carlo results to deal with a number of cases of interest. These include Fe, Co, and Ni, as well as a selection of half‐metallic ferromagnets and diluted magnetic semiconductors which are important for the novel field of spin‐electronics (spintronics). Here the detection of different exchange mechanisms is emphasized. A brief excursion into the long‐range order of low‐dimensional systems like thin magnetic films closes this chapter.
Exchange Coupling in Magnetic Multilayers
Authors: Edwards David M. , Umerski Andrey
Published: December 2007

After a brief historical introduction, the origin of interlayer exchange coupling (IEC) in magnetic multilayers is explained with an emphasis on the role of quantum well states in the nonmagnetic spacer layers. Analytic results for a simple model are given and techniques for quantitative calculation of IEC in real systems are described. A full discussion is given on mechanisms for biquadratic exchange coupling and the temperature dependence of IEC arising from single‐electron and spin‐wave excitations. Theory and experiment are compared for systems with noble metal, transition metal, antiferromagnetic metal, and insulating spacers. Open questions are identified, particularly an order‐of‐magnitude discrepancy between theory and experiment for the strength of IEC in the case of transition‐metal spacers.
Magnetic Superconductors
Authors: Buzdin A. , Flouquet J.
Published: December 2007

We review the main mechanisms of the interplay between magnetism and superconductivity, and discuss first the properties of the conventional s‐wave antiferromagnetic and ferromagnetic superconductors. In the case of ferromagnetism, its antagonism with superconductivity leads to spectacular effects such as a reentrant superconductivity and the domain magnetic structure formation.

It is now accepted that in heavy‐fermion compounds (HFCs) the superconductivity is unconventional. Here we analyze the (
P
,
T
) phase diagram with special focus on the stability of the different phases at
T
 → 0 K. In the recently discovered ferromagnetic heavy‐fermion superconductors, the Cooper pairing appears to be a triplet. The studies of the properties of these compounds will certainly open a new chapter in the physics of superconductivity.

We also discuss the particularities of the proximity effect in superconductor–ferromagnet heterostructures: the damped oscillatory behavior of the Cooper pair wave function and the conditions for the novel π‐Josephson junctions formation, which open an interesting perspective for the potential applications of these structures.
Magnetization Configurations and Reversal in Small Magnetic Elements
Authors: Kläui Mathias , Vaz Carlos António Fernandes
Published: December 2007

This chapter presents an overview of the magnetization configurations and reversal in magnetic structures ranging from a few nanometers to a few micrometers in size that can be described using the theory of micromagnetics. A range of techniques for the characterization of magnetic structures is introduced and the theoretical micromagnetism background, including the energy terms governing the magnetic properties, are discussed. The simplest case of a single domain system with uniform magnetization is treated within the framework of the Stoner–Wohlfarth theory, and experimental examples of such systems are presented. The magnetization configurations in larger systems that exhibit nonuniform magnetization are discussed in detail with a particular emphasis on experimental examples for the geometries that have been studied most often, such as discs, rings, rectangles, wires and pillars. Theoretically, the formation of these states is explained as a result of the interplay between the different magnetic energy terms; multidomain states that occur for larger elements are also introduced. The dynamic properties of the reversal of these elements are addressed, starting with the evaluation of the Landau–Lifshitz–Gilbert equation to obtain the trajectories for single domain particles. This is then extended to cover the nonhomogeneous reversal of nonuniform states. The elementary processes occurring during nonhomogeneous reversal are introduced and used to explain the magnetization reversal in a set of instructive examples.
Magnetization Dynamics: Thermal‐driven Noise in Magnetoresistive Sensors
Authors: Zhu Jian‐Gang
Published: December 2007

The development of spin‐valve and magnetic tunnel junction read sensors in hard disk drives has enabled tremendous reduction of data track width, leading to the tremendous increase of storage capacity, over the past decade. As the physical dimensions of the read sensors decrease into the deep submicron regime, thermally excited magnetization precession in the sensing magnetic layer becomes nonnegligible with amplitude comparable to that induced by magnetic flux from written data bits in disk media. This article provides a detailed analysis, based on the phenomenological Gilbert damping, of the nature of the thermally excited magnetization precession and the resulting noise temporal and spectral characteristics in the read sensors for hard disk drive applications. Comparison between the analysis and experimental measurements shows a remarkable agreement. Previous research on this subject is also reviewed.
Magnetic Modes in Circular Thin Film Elements, Experiment and Theory
Authors: Back Christian H. , Buess Matthias
Published: December 2007

In this chapter we review recent advances in the field of magnetization dynamics in small, confined structures. We limit ourselves to a particularly simple magnetic object which nevertheless exhibits various interesting magnetic modes on various timescales. We investigate a ferromagnetic disk in the flux‐closed state. In this configuration, the magnetic flux circulates around the element and leads to a polarized vortex core with its magnetization pointing out of the plane of the element. We show that time‐resolved Kerr microscopy is able to reveal the details of the magnetostatic modes of these elements. We also present some hints for the vortex core motion and the switching of the vortex core.
Theory of Spin‐transfer Torque
Authors: Stiles Mark D.
Published: December 2007

In magnetic multilayers, the spin‐polarized currents flowing between the magnetic layers can exert torques on the magnetizations of the layers when the magnetizations are not collinear. The theory of these spin‐transfer torques is developed in terms of semiclassical transport calculations coupled with quantum‐mechanical calculations of the behavior of spins at interfaces. The result is an expression for the torque in terms of the geometry of the devices and the magnetic configuration.
Microwave Generation in Magnetic Multilayers and Nanostructures
Authors: Rippard William H. , Pufall Matthew R.
Published: December 2007

We present an overview of the coherent magnetic precessional dynamics induced by the spin‐transfer effect in magnetic nanostructures. The precessional frequencies of the magnetic oscillators can be tuned over a range of several gigahertz by varying the dc current through the devices. The oscillation frequencies also depend on the applied magnetic field, resulting in a nanoscale oscillator that can be tuned from a few gigahertz to greater than 40 GHz. Even at room temperature, the linewidths of these excitations are often only a few megahertz wide. This gives quality factors for the excitations of more than 18 000 at the highest frequencies. As the direction of the applied field changes from parallel to perpendicular to the film plane, the power output from the structures increases by several orders of magnitude. For fields applied nearly perpendicular to the film plane, the high‐frequency voltage output from the device can be a significant fraction of the maximum voltage expected from the giant magnetoresistance effect. The nanoscale oscillators also display a number of attributes making them attractive for potential technological applications. These include the ability to frequency modulate the devices, phase lock them to external reference signals, and electronically control their phase relative to that of an input signal.
Electron Holography of Ferromagnetic Materials
Authors: McCartney Martha R. , Smith David J.
Published: December 2007

Electron holography in the transmission electron microscope provides a powerful approach for characterizing nanoscale ferromagnetic materials. By measuring the phase shift of an electron beam that has passed through the magnetic field of the sample, quantitative measurement at the nanometer scale can be achieved. Thus, the technique allows both visualization as well as quantification of magnetic fields with high spatial resolution and sensitivity. Off‐axis electron holography is the operating mode that is most commonly used. The theoretical basis and experimental geometry for the technique are described. Representative examples of a range of ferromagnetic materials are then described in more detail. Finally, prospects and problems for future developments are briefly discussed.
Spin‐polarized Low Energy Electron Diffraction
Authors: Elmers Hans‐Joachim
Published: December 2007

We review recent progress in the understanding of the physics of ultrathin ferromagnetic films and surfaces that has been made using elastic spin‐polarized low‐energy electron diffraction (SPLEED). Further development of the experimental technique including high efficient electron sources, spin manipulation and imaging allows a wide range of applications. We report on a quantitative comparison of relativistic dynamical scattering calculations with SPLEED experiments on Fe(110) surfaces and Fe(100)/W(100) thin films leading to an understanding of the spatial distribution of spin densities. Exploiting the surface sensitivity in combination with the large asymmetry of SPLEED, it becomes feasible to investigate magnetic order in low‐dimensional systems and nanostructures in the vicinity of the Curie temperature. We analyze possibilities to improve electron polarization detectors using SPLEED at very low energies.
Spin‐polarized Low Energy Electron Microscopy
Authors: Bauer Ernst
Published: December 2007

Spin‐polarized low‐energy electron microscopy (SPLEEM) is the imaging counterpart to spin‐polarized low‐energy electron diffraction (SPLEED). Therefore, it has the same possibilities and limitations as SPLEED but allows the study of the magnetization distribution in the top several atomic layers of crystals and highly oriented thin films. This chapter discusses the basics of the method, its experimental realization, the experimental procedures, and its applications to the study of the magnetization distribution in thin films as a function of film thickness, temperature, and magnetic field.
Investigation of Ultrathin Ferromagnetic Films by Magnetic Resonance
Authors: Baberschke Klaus
Published: December 2007

The microwave spectroscopy in magnetism exists in two versions: (i) The electron paramagnetic resonance (EPR) at which magnetic dipole transitions are excited between various Zeeman levels. (ii) The ferromagnetic resonance (FMR), here the applied magnetic fieldHproduces a uniform torque motion on the total magnetization. Thus the technique is suitable for studying magnetism above and below the Curie temperature. Moreover, the technique is sensitive down to 1010–1014spins, that is, fractions of a para‐ or ferromagnetic monolayer. For nanomagnetism the FMR/EPR techniques are combined with state‐of‐the‐art ultrahigh vacuum (UHV) technique, allowing an in situ study of uncapped magnetic monolayers in UHV. This article gives an overview of three aspects of current research: Firstly, the experimental details of UHV‐FMR. Secondly, the static parameters of the magnetism in monolayers: orbital and spin magnetic moments,g‐factor, the magnetic anisotropy energy (MAE), and the interlayer exchange coupling (IEC) of multilayers. Thirdly, from the linewidth of the magnetic resonance signal one deduces information on critical spin fluctuations, Gilbert damping, and magnon–magnon scattering. Of course, the FMR/EPR technique and its analysis of the spectra are well established. However, the combination with in situ UHV preparation opens a new field of research. Todays ab initio calculations of the magnetism of magnetic monolayers and nanostructures will be discussed and compared with the experimental FMR/EPR results.
Scanning Probe Techniques:
MFM
and
SP
‐
STM
Authors: Schwarz Alexander , Bode Matthias , Wiesendanger Roland
Published: December 2007

This chapter surveys the basic concepts, experimental conditions, modes of operation, tip preparation, and the contrast mechanisms of two magnetic‐sensitive scanning probe techniques, that is, magnetic force microscopy (MFM) and spin‐polarized scanning tunneling microscopy (SP‐STM). The strength and limitations of these imaging techniques are exemplified by presenting results obtained on numerous sample systems including magnetic hard disks, epitaxial surfaces, and nanoparticles at various temperatures and external fields.
Alternative Patterning Techniques: Magnetic Interactions in Nanomagnet Arrays
Authors: Ferré Jacques , Jamet Jean Pierre
Published: December 2007

Novel high‐resolution top‐down patterning techniques can be an alternative way to usual lithography fabrication methods for preparing arrays of quasi‐identical thin ferromagnetic nanoelements. One reports essentially on the following techniques: (i) ion beam lithography, (ii) direct writing by scanning a Ga focused ion beam (FIB), (iii) film deposition on prepatterned templates. The physical origin of soft magnetic patterning by He or Ga ions in thin‐film structures at low dose is discussed. All these techniques allow to prepare dense arrays of nanodots with negligible magnetic interaction that are among the best candidates for fabricating discrete perpendicular magnetic recording media with ultrahigh density. A review on advantages and limitations of studies of nanodot arrays is given. By increasing the Ga ion dose in narrow FIB lines separating ferromagnetic Pt/Co/Pt nanodots, the interdot magnetic interaction can be varied and controlled from exchange to dipolar. This gives the opportunity to study and analyze static and dynamic behavior of coupled macrospin assemblies.
Epitaxial Heusler Alloys onIII‐VSemiconductors
Authors: Hesjedal Thorsten , Ploog Klaus H.
Published: December 2007

At the basis of future applications of spin electronics are ferromagnetic films that have a Curie temperature above room temperature, a crystal structure that allows for epitaxial growth on common semiconductor surfaces, and a high degree of spin polarization at the Fermi level. A class of ternary compounds, the so‐called Heusler alloys, combine these requirements as they are lattice‐matched to many compound semiconductors, have a compatible crystal structure (face‐centered cubic), and show high Curie temperatures. Moreover, calculations suggested that some Heusler alloys may belong to the magnetic class of half‐metals that is characterized by a 100% spin polarization at the Fermi level. We review the work on epitaxial‐Heusler alloy films on semiconductor surfaces. Special emphasis is laid on molecular‐beam epitaxy (MBE), as this growth method allows for anin situcontrol of the growth and structure of the material. Taking Co2FeSi on GaAs as an example, the structural and magnetic properties of MBE‐grown samples will be discussed.
Soft Magnetic Materials—Nanocrystalline Alloys
Authors: Herzer Giselher
Published: December 2007

Nanocrystalline Fe‐based alloys combine the advantageous properties of various soft magnetic materials, that is, the high saturation induction of Fe‐based alloys, the high permeability and low magnetostriction of permalloys or amorphous Co‐based alloys and the favorable high‐frequency behavior of ferrites or amorphous metals. The materials to be highlighted are devitrified glassy Fe–Cu–Nb–Si–B alloys, which, owing to their outstanding properties, have meanwhile successfully entered into application. The microstructure consists of randomly oriented, about 10–15‐nm small bcc‐FeSi grains embedded in a ferromagnetic amorphous minority matrix. The article surveys the key factors from which the extraordinary properties of this new class of soft ferromagnets derive. Thus, the local magnetocrystalline anisotropies are largely averaged out since their orientation is randomly fluctuating on a scale much smaller than the domain wall width. The structural phases formed upon crystallization lead to a low or vanishing saturation magnetostriction. Like in other soft magnetic materials, annealing‐induced anisotropies finally allow to tailor the hysteresis loop according to the various demands of application.
Rare‐earth Nanocrystalline and Nanostructured Magnets
Authors: Marinescu Melania , Gabay Alexander , Hadjipanayis George C.
Published: December 2007

The contribution presents the recent advances in permanent magnets with nanocrystalline or nanophase structures based on rare‐earth compounds. The main classes of magnets discussed are the nanocrystalline single‐phase and nanocomposite R2Fe14B‐based magnets; nanocomposite Nd–Fe carbides; bulk‐hardened R2Co17and RCo5nanocrystalline magnets; Sm(Fe,M)12, SmFe3, and Sm5(Fe,M)17nanocrystalline magnets; Sm2Fe17nitrides and carbides; and Nd(Fe,M)12nitrides and carbides (R and M denotes rare‐earth elements and transition metals, respectively). The magnetic hardening mechanism and the relation with the particular morphologies (grain size and phase constitution) of the different types of nanocrystalline and nanostructured magnets are reviewed.
Heusler Alloys
Authors: de Groot Robert A.
Published: December 2007

Half‐metallic magnetism was discovered first in a Heusler C1b alloy. Since there is no simple univocal experiment to test for half‐metallicity, electronic structure calculations have played an important role in the discovery, explanation and prediction of half‐metals. Experimental work related to half‐metallicity is reviewed. Attention is given to the special role of surfaces and interfaces. Half‐metallic anti‐ferromagnetism (100% spin‐polarization without a magnetization) is discussed. Finally, the computational and experimental status of heusler L21 alloys is summarized.
Ferrimagnetic Insulators
Authors: Brabers Victor A.M.
Published: December 2007

Ferrimagnetic insulators
Most of the useful ferrimagnetic insulators are found in the mixed oxide systems with a high concentration of iron, the so‐called ferrites, which show at room temperature a substantial magnetization and makes them suitable for a large variety of applications. Soft magnetic ferrites are usually encountered in the spinel and garnet structure ferrites, whereas hard‐magnetic ferrites crystallize in a hexagonal structure. A short discussion is presented of the various types of ferrites in addition to a more extended presentation of the more recent developments about the properties of magnetite, Fe
3
O
4
.

In particular the mechanism of the electronic structure and the mechanism of the electrical conduction as well as the mechanism of the Verwey transition are discussed because of the importance and possibilities of Fe
3
O
4
in spintronic applications.
Template‐based Synthesis and Characterization of High‐density Ferromagnetic Nanowire Arrays
Authors: Nielsch Kornelius , Stadler Bethanie J. H.
Published: December 2007

This chapter covers the synthesis and characterization of magnetic nanowire arrays that are grown inside nanoporous templates. Applications for such arrays include patterned recording media, magnetic and acoustic sensors, and other avant‐garde applications that will be envisioned once the fundamental properties and performances of these arrays are better known. Several nanoporous templates are introduced, but this chapter primarily focuses on results using anodic alumina templates. The templates are filled with ferromagnetic metals via electrodeposition either using DC deposition onto an electrode after the removal of a barrier oxide or using AC deposition to eliminate the need to remove the oxide. Several typical electrolyte recipes are given (Co, Fe, FeGa alloys, Ni, and NiMn), and the details of both techniques are discussed. Methods for controlling the magnetic properties of the arrays by the choice of nanowire material, diameter, and interpore spacing, in addition to external fields, are detailed. Next, numerical simulations are presented in order to investigate the switching behavior of magnetic nanowires. Perfect hexagonal arrangements of pores on a square centimeter scale are demonstrated using imprint lithography. Finally, the applications of recording and sensors are discussed in detail.
Hard Magnetic Films
Authors: Shima Toshiyuki , Takanashi Koki
Published: December 2007

Hard magnetic films, showing high magnetocrystalline anisotropy, have been attracting much attention recently for application to magnetic devices since the critical grain size for superparamagnetic limit can be reduced to the nanometer scale. In this chapter, the fabrication techniques and the magnetic properties of hard magnetic films are reviewed. Firstly, the fundamental phenomena and models which are important for the understanding of hard magnetic properties in thin films are described. Secondly, the recent developments of hard magnetic films and their potential applications are mentioned. Particularly the relationship between micro‐/nanostructure and the magnetization process (coercivity mechanism) is discussed in detail for rare earth–transition metal alloy films and L1
0
‐ordered FePt films.
Molecular Nanomagnets
Authors: Wernsdorfer Wolfgang
Published: December 2007

Molecular nanomagnets (or single‐molecule magnets (SMMs)) have attracted much interest in recent years both from experimental and theoretical points of view. These systems are organometallic clusters characterized by a large‐spin ground state with a predominant uniaxial anisotropy. The quantum nature of these systems makes them very appealing for phenomena occurring on the mesoscopic scale, that is, at the boundary between classical and quantum physics. Below their blocking temperature, they exhibit magnetization hysteresis, the classical macroscale property of a magnet, as well as quantum tunneling of magnetization (QTM) and quantum phase interference, the properties of a microscale entity. QTM is advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states for quantum computing, but it is a disadvantage in others such as information storage. It is widely accepted that SMMs have a potential for quantum computation, in particular, because they are extremely small and almost identical, allowing to obtain, in a single measurement, statistical averages of a larger number of qubits. This chapter introduces a few basic concepts that are needed to understand the quantum phenomena observed in molecular nanomagnets and it concludes by mentioning new trends of the field of molecular nanomagnets toward molecular spintronics.
Ferromagnetic Manganite Films
Authors: Moshnyaga Vasily , Samwer Konrad
Published: December 2007

We discuss the structure and electronic properties of ferromagnetic perovskite manganites with general formula Re

1−
x

Ae

x

MnO
3
(Re = La, Pr, Nd and Ae = Ca, Sr, Ba). These magnetic oxides being strongly correlated electronic systems show metal‐insulator and ferro‐paramagnetic phase transitions as well as charge/orbital ordering. Moreover, competition among charge, spin, and lattice degrees of freedom can lead to mesoscopic electronic inhomogeneity known also as electronic phase separation. Focusing on the magnetotransport properties in thin manganite films, we will show how the fundamental phenomena mentioned in the preceding text interplayed with specific thin‐film‐related characteristics like epitaxy stress, growth mode, and microstructure, govern various magnetoresistance (MR) effects—colossal magnetoresistance (CMR), tunneling, and anisotropic MR.
Spin‐dependent Tunneling: Role of Evanescent and Resonant States
Authors: Tsymbal Evgeny Y.
Published: December 2007

There are two important factors which control the spin polarization of the tunneling current in epitaxial magnetic tunnel junctions (MTJs), in addition to the bulk band structure of ferromagnetic electrodes: evanescent states in the insulating barrier and the electronic structure of the ferromagnet/barrier interface. We consider several theoretical models illustrating the significance of these two factors in different kinds of MTJs. Symmetry of the evanescent states in the barrier selects those spin‐polarized bands in the ferromagnetic electrodes that are able efficiently tunnel through the barrier. This mechanism is responsible for large values of tunneling magnetoresistance (TMR) predicted and observed in crystalline MTJs based on an MgO insulating barrier and for the negative spin polarization of Co/SrTiO
3
/Co MTJs with bcc Co electrodes. The interface bonding may result in the appearance of interfaces resonant states that dramatically affect the spin polarization of the tunneling current. These states explain a decrease of TMR in Fe/MgO/Fe(001) MTJs for small barrier thickness. The presence of an interface band at the oxidized Co(001) surface causes the spin polarization of the tunneling current across vacuum to be negative, as opposed to that predicted for the clean Co surface. The strong interface bonding between Co and O atoms at the interface in Co/Al
2
O
3
/Co MTJs explains positive values of the spin polarization observed experimentally.
Diluted Ferromagnetic Semiconductors—Theoretical Aspects
Authors: Dietl Tomasz
Published: December 2007

This chapter reviews theoretical understanding of ferromagnetic response that has been detected in diluted magnetic semiconductors (DMS). Particular attention is paid to those ferromagnetic DMS in which
no
precipitation of other crystallographic phases has been observed. It is argued that these materials can be divided into three categories. The first consists of (Ga,Mn)As, heavily doped p‐(Zn,Mn)Te, and related compounds. In these solid solutions, the theory built on p–d Zener's model of hole‐mediated ferromagnetism and on either the Kohn‐Luttinger
kp
theory or the multiorbital tight‐binding approach describes qualitatively, and often quantitatively, thermodynamic, micromagnetic, optical, and transport properties. Moreover, the understanding of these materials has provided a basis for the development of novel methods enabling magnetization manipulation and switching. To the second group, belong compounds in which a competition between long‐range ferromagnetic and short‐range antiferromagnetic interactions and/or the proximity of the localization boundary lead to an electronic nanoscale phase separation that results in characteristics similar to colossal magnetoresistance oxides. Finally, in a number of compounds a chemical nanoscale phase separation into the regions with small and large concentrations of the magnetic constituent is present. Methods of controlling the spinodal decomposition and possible functionalities of these systems are outlined.
Spin‐transfer in High Magnetic Fields and Single Magnetic Layer Nanopillars
Authors: Kent Andrew D.
Published: December 2007

This chapter reviews studies of the physics of spin transfer in high magnetic fields in bilayer and single magnetic layer nanopillars. The focus is on phenomena associated with the action of spin currents on the background magnetization of thin nanometer‐scale ferromagnetic layers, known as
nanomagnets
. Spin currents are shown to lead to magnetic hysteresis in large fields perpendicular to the layers in bilayer nanopillars. This is consistent with the standard model of spin transfer within a macrospin approximation. Spin‐transfer‐induced excitations also occur in single magnetic layer nanopillars. This shows that the most elementary samples that exhibit spin transfer consist of just a single thin magnetic layer, not two magnetic layers. Physics beyond the macrospin and one‐dimensional transport models is necessary to understand such excitations. Nonuniform spin‐wave excitations are also seen in the traditional bilayer structures, which experiments reveal to have a rich phase diagram of current‐induced magnetic excitations.
Electrical Double Layers: Theory and Simulations
Authors: Schmickler Wolfgang
Published: December 2007

The sections in this article are

Introduction

Gouy–Chapman Theory and its Extensions

Theoretical Methods and Principles of Computer Simulations

Integral Equations

Computer Simulations

Monte Carlo simulations

Molecular Dynamics

Car–Parinello Method

Electronic Structure Calculations

Models for the Solution

Field‐Theoretical Approach to the Double Layer

Ensembles of Hard Spheres

The Role of the Metal

Qualitative Considerations

The Jellium Model

Calculations for Metal Clusters

The Metal–Solution Interface

Jellium in Contact with Model Solutions

Molecular Dynamics Simulations

Car–Parinello‐Type Simulations

Rough Electrodes

Liquid–Liquid Interfaces

Verwey–Niessen Theory

Capillary Waves

Lattice Gas Model

Conclusion

Acknowledgments
Phase Transitions in Two‐dimensional Adlayers at Electrode Surfaces: Thermodynamics, Kinetics, and Structural Aspects
Authors: Wandlowski Thomas
Published: December 2007

The sections in this article are

Introduction

Thermodynamic Aspects

Phase Transitions and Order Parameter

Adsorption Isotherms and Lateral Interactions

Kinetics of 2DPhase Formation and Dissolution

Diffusion, Adsorption, Autocatalysis

Nucleation and Growth Mechanisms

Nucleation

Growth

Coupling of Nucleation and Growth

Dissolution of 2DCondensed Monolayers

Examples

Phase Transitions in Anionic Adlayers

Introduction

Phase Formation in Halide Adlayers

Phase Transitions in Adlayers of Oxoanions

Phase Transitions inUPD—Adlayers

Introduction

Underpotential Deposition of Copper Ions onAu(hkl)

Underpotential Deposition of Copper Ions onPt(hkl)

Underpotential Deposition of Lead onAg(hkl)

Phase Transitions in Organic Monolayers

General Aspects

Thermodynamic Aspects

Kinetic Aspects

Case Study I—Coumarin at the Mercury–Aqueous Electrolyte Interface

Case StudyIII—2,2′‐Bipyridine (2,2′‐BP) onAu(hkl)

Conclusion and Outlook

Acknowledgment
In
s
itu
FTIR
as a Tool for Mechanistic Studies. Fundamentals and Applications
Authors: Nart Francisco C. , Iwasita Teresa
Published: December 2007

The sections in this article are

Historical Overview

The External Reflectance Spectroscopy

Fundamentals

The Band Intensity

Surface Selection Rule

Experimental Setup

Transport Effects in the Thin Electrolyte Film

Infrared Spectroscopy under Equilibrium Conditions. Study of Adsorbed Sulfate Ions on Single‐crystal Electrode Surfaces

The Adsorption of Anions (The Electrical Double Layer)

The Adsorption of Sulfate on
M
(111) Single‐crystal Electrodes

The Sulfate Ion Adsorbed on the
M
(100) and (110) Single‐crystal Electrodes

Infrared Spectroscopy under Nonequilibrium Conditions. Study of Systems Relevant in Electrocatalysis

Carbon Monoxide

Adsorption and Oxidation of
CO
on Polycrystalline Substrates

Adsorption and Oxidation of
C
O on Single‐crystal Substrates

Methanol

Ethanol

Potential Dependence of the Band Intensities

Final remarks

Acknowledgments

Appendix
Linear Sweep and Cyclic Voltammetry
Authors: Speiser Bernd
Published: December 2007

The sections in this article are

Introduction

Historical Background

Potential Scan Voltammetries—Definitions

Scope of the Chapter

Theory of Potential Scan Voltammetries

General

Reversible Electron Transfer

Kinetics of Electron Transfer

Coupled Homogeneous Chemical Kinetics

Adsorption and Surface‐Bound Redox Species

Nonlinear Diffusion

Restricted Diffusion

Simulation

Practical Considerations

Electrodes and Cells

Solvents and Supporting Electrolytes

Experimental Limitations

Artifacts and how to Avoid Them

Present Methodological Developments

Voltammetry at Ultramicroelectrodes

Fast Scan Techniques

Voltammetry without Supporting Electrolyte

Voltammetry Under Hydrodynamic Conditions

Voltammetric Spectroelectrochemistry

Derivative Voltammetry

Semiintegral (“Convolution”) and Semiderivative Voltammetry

Applications

Typical Voltammograms—Classical Applications

Selected Recent Examples

Conclusion

Acknowledgments
Hydrodynamic Electrodes
Authors: Mount Andrew R.
Published: December 2007

The sections in this article are

Introduction

Rotating Disc Hydrodynamics

Rotating Disc Electrode (
RDE
)

The Rotating Ring Disc Electrode (
RRDE
)

The Optical Rotating Disc Electrode (
ORDE
)

Solution Flow Hydrodynamic Systems

The Wall‐tube Electrode (
WTE
)

The Wall‐jet Electrode (
WJE
)

The Wall‐jet Ring‐disc Electrode (
WJRDE
)

The Tube or Tubular Electrode (
TE
)

The Channel Electrode (
CE
)

The Double Channel Electrode (
DCE
) and Double Tube Electrode (
DTE
)

Numerical Calculations

Microhydrodynamic Systems
Biosensors
Authors: Schuhmann Wolfgang , Bonsen Eva Maria
Published: December 2007

The sections in this article are

Introduction

Basic Principles and Setup

Application of Biosensors. Principal Considerations

Biorecognition Elements

Catalytic Biorecognition Elements

Bioaffinity Recognition Elements

Transducers and Instrumentation

Amperometric Electrodes

Potentiometric Sensors

Conductometric and Impedimetric Transducers

Coupling of Biorecognition Elements and Transducers

Specific Features of Electrochemical Biosensors

Amperometric Biosensors

Shuttle Mechanism Using Free‐diffusing Natural Redox Mediators

Artificial Redox Compounds as Free‐diffusing Electron‐Transfer Mediators

Immobilized Redox Mediators—“Electroenzymes”

“Wired” Enzymes by Means of Redox Hydrogels

Conducting Polymers

Direct Electron Transfer between Redox Enzymes and Electrodes

Potentiometric Biosensors

Potentiometric Enzyme Biosensors

Potentiometric Immunosensors

Field‐effect Transistors

Conductometric and Impedimetric Biosensors

Miniaturization and Future Aspects

Miniaturized Transducers

Advantages and Problems of Miniaturized Biosensors

Multisensor Arrays and Sensor Chips
Transport Phenomena in Electrolytic Corrosion
Authors: Landolt Dieter , Frankel Gerald S.
Published: December 2007

The sections in this article are

Introduction

Ion Transport in Electrolytes

Generalized
B
utler–
V
olmer Equation

Concentration Overvoltage

Effect of Mass Transport on Corrosion Reactions