bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rare‐earth Intermetallics for Permanent Magnet Applications
Authors: Fidler Josef , Suess Dieter , Schrefl Thomas 
Published: December 2007

Abstract

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

Abstract

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

Abstract
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

AbstractThe 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

AbstractThe 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

Abstract
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

Abstract
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

Abstract
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

AbstractThe 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

AbstractAfter 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

AbstractThe 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

AbstractWe 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).
Ferromagnetic Semiconductors
Authors: Matsukura Fumihiro , Ohno Hideo 
Published: December 2007

Abstract
Properties of ferromagnetic semiconductors based on III–V compound semiconductors and their heterostructures and device structures are presented. The emphasis is placed on the ways to determine basic properties and understanding of the properties of (Ga,Mn)As. Carrier‐induced ferromagnetism in these materials allows us not only to probe the magnetism by electrical means but also to control magnetism and magnetization by electrical means. The possibility of having ferromagnetic semiconductors with high transition temperatures is also discussed.
Magnetic Tunnel Junctions
Authors: Parkin Stuart , Yang Hyunsoo , Yang See‐Hun , Hayashi Masamitsu 
Published: December 2007

AbstractThe sections in this article areIntroductionFundamentals of Magnetic Tunnel Junctions (MTJs)Influence of Chemical Bonding on Spin‐Polarized TunnelingInfluence of Wave‐Function Symmetry on Spin‐Polarized TunnelingRelationship of Tunneling Magnetoresistance to Tunneling Spin PolarizationTemperature and Bias Voltage Dependence ofTMRSpin‐Dependent Tunneling in Other SystemsConclusion
Microwave Excitations in Spin Momentum Transfer Devices
Authors: Mancoff Frederick B. , Kaka Shehzaad 
Published: December 2007

AbstractThe spin‐transfer torque on a nanomagnet from a spin‐polarized electric current can excite a hysteretic reversal or high‐frequency precession of the nanomagnet. The precessing magnetic state in giant magnetoresistance point contacts can be frequency tuned from <5 to >40 GHz, with narrow linewidths of <5 MHz, as a function of applied current and magnetic field making these devices promising for nanoscale microwave oscillator applications. We discuss measurements of two aspects of the spin‐transfer precession state: the point contact area dependence of spin‐transfer precession; and the observation of phase locking between independent spin‐transfer oscillators. For increasing contact size from 35 nm to almost 300 nm diameter, both the decreasing slope of frequency versus current and the increasing critical current were fit by a model of a precession area extending past the contact edge by a ring of width ≈50 nm. For two contacts of nominal 80 nm diameter and electrically connected in parallel, we observed phase locking of the two spin‐transfer resonances for intercontact spacings <200 nm. In other devices with two contacts with independent electrical control, phase locking was observed at a spacing of 500 nm as the frequency of one contact was tuned toward the frequency of the other. The area‐dependence results are important with regards to fabrication and scaling of future spin‐transfer applications, while the existence of phase locking between spin‐transfer oscillators is essential for the coherent control of point contact arrays with increased output power as needed for practical devices.
The Magnetic Resonance Force Microscope
Authors: Hammel P. Chris , Pelekhov Denis V. 
Published: December 2007

AbstractThe magnetic resonance force microscope (MRFM) is a novel scanned probe instrument which combines the three‐dimensional imaging capabilities of magnetic resonance imaging with the very high sensitivity of force detection. This approach enables high spatial resolution in nondestructive, microscopic studies and imaging of a broad range of materials. Magnetic resonance detection of an individual electronic moment has been demonstrated using MRFM. Here we discuss the principles, method, and techniques of MRFM. While focusing on detailed discussions of the experimental approaches used, we also point out several successful applications thus demonstrating the broad potential of this novel technique.
Spin Engineering in Quantum Well Structures
Authors: Myers Roberto C. , Gossard Arthur C. 
Published: December 2007

Abstract

The spatial confinement of carriers to two‐dimensional systems has led to many recent advances in the field of semiconductor spintronics. Quantum wells offer a unique means for controlling the interactions of free carrier spins with localized magnetic‐ion spins and nuclear spins, and have the advantage of a high level of technological versatility via advanced growth techniques, most notably molecular‐beam epitaxy. Additionally, quantum wells offer advantageous optical properties for probing and polarizing spin. We review recent developments in semiconductor spintronics, in which electric and magnetic fields are used to polarize, orient, and couple quantum‐confined spins. Heterostructure design for the engineering of
g
‐factor, hyperfine coupling, and magnetic exchange interactions are discussed.
Manipulation of Spins and Coherence in Semiconductors
Authors: Stern Nathaniel P. , Berezovsky Jesse , Ghosh Sayantani , Awschalom David D. 
Published: December 2007

Abstract
The ability to optically measure coherent ensembles of spin‐polarized carriers in semiconductors has enabled many advances in the study of spin dynamics. Recent experiments reveal new capabilities to generate spin polarization through all‐electrical means without external magnetic fields. The ability to both manipulate and transport spins at GHz frequencies and micron length scales has created much interest in semiconductor spintronics. We review developments in the study of coherent spins in semiconductors, including methods for the electrical generation of spin polarization such as current‐induced spin polarization and the recently discovered spin Hall effect. Additionally, we discuss spin coherence in magnetic semiconductors, which offer a unique class of materials where electrical and magnetic phenomena can be combined.
Spin‐dependent Transport of Carriers in Semiconductors
Authors: Winkler Roland 
Published: December 2007

Abstract
This chapter reviews spin‐dependent transport of carriers in homogenous three‐dimensional and two‐dimensional semiconductors. We begin with a discussion of optical orientation of electron spins, which allows both the creation and detection of spin‐polarized carriers in semiconductors. Then we review nonequilibrium spin flow including spin drift and diffusion caused by electric fields and concentration gradients. A controlled spin precession is possible both in external magnetic fields and in effective magnetic fields due to a broken inversion symmetry. Although the Coulomb interaction does not couple to the spin degree of freedom, it affects the spin‐dependent transport via the spin Coulomb drag. In gyrotropic media, the optical creation of spin‐oriented electrons gives rise to spin photocurrents, which reverse their direction when the radiation helicity is changed from left‐handed to right‐handed. The reverse process is possible, too, that is, an electric current in a gyrotropic medium gives rise to a spin polarization in the bulk of the sample.
Electrical Double Layers. Double Layers at Single‐crystal and Polycrystalline Electrodes
Authors: Lust Enn 
Published: December 2007

Abstract
The sections in this article are

General Aspects

The Potential of Zero Charge and Electric Double‐layer Structure

Differential Capacitance of Electrode–Electrolyte Solution Interface

Electrical Double‐layer Structure at Solid Electrodes

Surface Roughness of Solid Electrodes

The Applicability of the Gouy–Chapman–Stern–Grahame Model to Solid Electrodes

Shape of
C
,
E
Curves

Parsons and Zobel Plot Method

Surface Roughness and Shape of Inner‐layer Capacitance Curves

Polycrystalline Electrode Models

Debye Length–dependent Surface Roughness Model

Electric Double Layer and Fractal Structure of Surface

Experimental Aspects. Short Review of Data

Silver

Gold

Copper

Lead

Tin

Zinc

Cadmium

Bismuth

Antimony

Iron

Nickel

Pt
‐group Metals

General Correlations

Zero‐charge Potential and Reticular Density of Planes

Potential of Zero Charge, Work Function, Interfacial Parameter, and Inner‐layer Capacitance

Data of Quantum‐chemical Calculations

Adsorption of Organic Compounds and Hydrophilicity of Electrode
Analyzing Electric Double Layers with the Atomic Force Microscope
Authors: Butt Hans‐Jürgen 
Published: December 2007

AbstractThe sections in this article areIntroductionSurface Forces in Aqueous ElectrolyteDLVOForcesEarly Surface Force MeasurementsThe Surface Forces ApparatusThe Osmotic Stress MethodThe Bimorph Surface Force ApparatusForce Measurements with theAFMThe Practice of Force MeasurementsThe CantileverThe Probe: Tip or Colloidal ParticleAn Instability: The Jump‐InAFM‐Related TechniquesTheory of Measuring Surface Forces with theAFMin Aqueous ElectrolyteDerjaguins ApproximationThe Electrostatic Double‐Layer ForceOther Surface Forces in Aqueous ElectrolyteAFMForce Measurements of the Electric Double LayerBetween Solid SurfacesHigh Surface PotentialsBetween Deformable SurfacesImaging Charge DistributionsConclusion and Outlook