bluuebunny/crossref_metadata_2025_split huggingface dataset:
Classical Spin Models
Authors: Nowak Ulrich 
Published: December 2007

Abstract
Classical spin models bridge the gap between a full electronic description of a magnetic material and conventional micromagnetism, where magnetic properties are calculated on the basis of a continuum theory for the energy of the system under consideration. Since spin models take into account magnetic configurations on an atomic level, they make it possible to investigate ferromagnets as well as antiferromagnets or even heterostructures composed of both of them. While well‐established methods exist for the calculation of thermal equilibrium properties, the investigation of thermally activated spin dynamics is a newer field of research which is currently developing.
One goal of this review is to give an overview on numerical approaches related to classical spin systems, where the most established methods are either a numerical solution of the Landau–Lifshitz–Gilbert equation with Langevin dynamics or Monte Carlo simulations. Special emphasis is laid on the relation between these two methods and on the possibility to quantify the steps of a Monte Carlo procedure in terms of realistic time intervals. Furthermore, as typical applications of these numerical techniques, this overview includes a description of thermally activated magnetization switching in cylindrical geometries as well as an introduction to the simulation of exchange bias.
Nonlinear Magnetization Dynamics in Nanomagnets
Authors: Serpico Claudio , Bertotti Giorgio , Mayergoyz Isaak D. , d'Aquino Massimiliano 
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.
Magnetic Properties of Systems of Low Dimensions
Authors: Allenspach Rolf 
Published: December 2007

Abstract

The topic of low‐dimensional ferromagnetism is presented by means of examples: three specific systems illustrate phase transitions, domain patterns, and domain walls. Stripe‐domain phases and their transformations are described in ultrathin, perpendicularly magnetized Fe/Cu films, and related to two‐dimensional phase transitions. The domain patterns in small elements are discussed in stepped Co/Cu(001), an in‐plane‐magnetized system with tunable anisotropy. A wealth of different domain patterns is observed, exhibiting a distinct size and thickness dependence. A microscopic investigation of domain walls that are confined to small elements and pinned at constrictions is performed in Fe
20
Ni
80
. The wall types and profiles are found to deviate strongly from those encountered in extended films. A comparison with micromagnetic simulations leads to insight into the energetics driving these modifications.
Domain Wall Propagation in Magnetic Wires
Authors: Ono Teruo 
Published: December 2007

Abstract
Experimental aspects of the domain wall (DW) propagation in magnetic nanowires are reviewed. In the first part, after an introduction of the detection technique of the DW propagation by using the giant magnetoresistance effect, the DW propagation by an external magnetic field including DW velocity measurements is described. In the second half, direct observation of the DW motion induced by an electrical current is presented. Magnetic force microscopy (MFM) is used to show that a single domain wall can be displaced back and forth by positive and negative pulsed‐currents.
Nonlinear Multidimensional Spin‐wave Excitations in Magnetic Films
Authors: Demokritov Sergej O. , Slavin Andrei N. 
Published: December 2007

AbstractSpin‐wave excitations provide a basis for the description of spatial and temporal magnetization distributions in magnetic samples under the general assumption that the total length of the magnetization vector is locally conserved. The magnetization dynamics in this case results in the precession of the magnetization vector and is described by the well‐known Landau–Lifshitz torque equation. Linear plane waves of magnetization (or spin waves) corresponds to a spatially nonuniform solution of this equation for relatively small precession angles. For larger precession angles the intrinsic nonlinearity of the Landau–Lifshitz equation should be taken into account, and a new basis of intrinsicallynonlinearspin‐wave excitations—multidimensional quasistable nonlinear spin‐wave packets formed as a result of the nonlinear interaction between the individual plane spin waves—should be used. In magnetic films, such intrinsic nonlinear spin‐wave excitations are the one‐dimensional spin‐wave solitons and two‐dimensional spin‐wave bullets. These nonlinear excitations can be experimentally studied and visualized by means of the space‐ and time‐resolved Brillouin light‐scattering technique. This chapter gives a brief description of the theory of nonlinear spin waves in magnetic films based on the classical Hamiltonian formalism, and a short summary of the experimental methods used for the investigation of spin‐wave processes. The description of different methods of excitation of nonlinear spin‐wave modes is given, and the examples of experimental investigations of bright, dark, spatial, and temporal one‐dimensional spin‐wave solitons, and the two‐dimensional propagating spin‐wave bullets are presented. A novel type of symmetry‐breaking Möbius solitons generated in a magnetic active ring with parametric pumping, as well as the standing evanescent spin‐wave bullet generated by spin‐polarized current in thin metallic films are also discussed. The chapter gives an overview of the recent experimental achievements in the field of nonlinear spin‐wave dynamics in magnetic films and relates these achievements to the progress in the general field of nonlinear wave dynamics.
Investigation of Domains and Dynamics of Domain Walls by the Magneto‐optical
K
err‐effect
Authors: Schäfer Rudolf 
Published: December 2007

Abstract
Kerr microscopy allows to image magnetic domains and magnetization processes in an optical polarization microscope. The method is based on the magneto‐optical Kerr effect, that is, the rotation of plane‐polarized light in dependence of the magnetization direction on reflection from a nontransparent sample. By means of an analyzer, this rotation is converted into a (in general weak) domain contrast that can be enhanced by digital image processing. Kerr microscopy is the most versatile domain imaging method with several advantages: (i) By digital enhancement, domain contrast can be seen on virtually all kinds of ferro‐ and ferrimagnetic materials. (ii) The Kerr effect is directly sensitive to the magnetization vector whose direction can also quantitatively be measured (at least in soft magnetic materials). (iii) There is no restriction in specimen size and shape, and samples can easily be manipulated during observation. (iv) Arbitrary magnetic fields can be applied, so that nucleation and magnetization processes can be observed in real time. (v) Kerr microscopy offers the potential of high‐speed observation of dynamic processes. (vi) The magneto‐optical information depth is some 10 nm in metals. This makes it possible to separately image the domains in multilayer structures. Drawbacks are (i) a limited lateral resolution to some tenths of a micrometer and (ii) the restriction to the imaging of surface domains in bulk materials. In this article, the possibilities of Kerr microscopy for the investigation of domains and domain dynamics are reviewed together with physical and technological fundamentals.
Magnetization‐induced Second Harmonic Generation
Authors: Kirilyuk Andrei , Rasing Theo 
Published: December 2007

Abstract
The magnetization‐induced effects in the nonlinear optical response of magnetic media—magnetization‐induced second‐harmonic Generation (MSHG)—lead to very strong and novel nonlinear magneto‐optical (MO) phenomena that appear to be very sensitive to magnetic interface properties. This surface/interface sensitivity of MSHG in combination with the very large MO effects has led to a fast development of this technique over the past decade. On the one hand, an extreme sensitivity of MSHG to the electronic and magnetic structure of clean surfaces has been successfully demonstrated. On the other hand, the penetration depth of light allows one to use this sensitivity to study buried interfaces in multilayer systems. Further experimental developments of the MSHG technique, like space‐ and time resolution as well as magnetization sensitive sum frequency generation, appear to be promising as well.
Investigation of Spin Waves and Spin Dynamics by Optical Techniques
Authors: Hillebrands Burkard , Hamrle Jaroslav 
Published: December 2007

Abstract
This review describes the current state of the art of optical techniques used to study the magnetization dynamics in ferromagnetic materials. Most optical techniques provide a spatial resolution defined by the wavelength limit of the used light. The techniques can be roughly divided into the two classes (a) frequency‐scale techniques such as Brillouin light scattering and Kerr effect ferromagnetic resonance and (b) timescale techniques such as time‐resolved, stroboscopic Kerr effect magnetometry. These techniques are presented and illustrated with selected experiments.
High‐energy Surface Spin Waves Studied by Spin‐polarized Electron Energy Loss Spectroscopy
Authors: Etzkorn Markus , Anil Kumar Parameswaran Sarala , Kirschner Jürgen 
Published: December 2007

Abstract
In this chapter, studies of high wave‐vector spin waves at surfaces are discussed. At present, the only technique that allows experimental access to this type of spin waves is spin‐polarized electron energy loss spectroscopy (SPEELS). In this experiment, a beam of spin‐polarized, monochromatic electrons is scattered from a magnetic sample. The scattered electrons are analyzed with respect to their wave vector and energy transfer to the sample. The excitation of spin waves results in specific loss features in the SPEEL spectra, as is shown on the example of three different systems, fcc Co on Cu(001), hcp Co on W(110), and tetragonal distorted thin Fe films on Co/Cu(001). In all three systems, the spin waves show a pronounced dispersion, that is, a dependence of the spin‐wave energy on the wave vector, which allows conclusions about the exchange interaction at the topmost surface layers. The spin‐wave loss features in the spectra also show a large intrinsic width that results from the strong damping of these excitations by the decay into electron–hole pairs. In this chapter, the results obtained by SPEELS are also compared to data measured by complementary experimental techniques and recent theoretical calculations.
Chemical Synthesis of Monodisperse Magnetic Nanoparticles
Authors: Wang Chao , Sun Shouheng 
Published: December 2007

Abstract

This chapter reviews briefly the recent advance in chemical synthesis of monodisperse magnetic nanoparticles. It covers mainly the syntheses of metallic Co, Fe, ferrite MFe
2
O
4
(M = Fe, Co, Mn), alloy FePt, CoFe, core/shell structured FePt/Fe
3
O
4
, and dumbbell‐like Au–Fe
3
O
4
nanoparticles. The unique magnetic properties observed from these nanoparticles are also described. Shape‐controlled synthesis and assembly of iron oxide and FePt nanoparticles are outlined as two examples to demonstrate that shape can be used to induce texture in a self‐assembled superlattice array.
Nanoimprint Technology for Patterned Magnetic Nanostructures
Authors: Chou Stephen Y. 
Published: December 2007

AbstractThis chapter describes the principle of nanoimprint lithography, different nanoimprint forms and their relative merits and shortcomings, key factors in nanoimprinting (masks, materials, pressing methods and imprinting pressure uniformity, material dispensing methods, vacuum, mold separation), examples of nanoimprinting in magnetic nanostructure fabrication, control of magnetic structure properties by patterning, the principle of quantized magnetic disks (QMDs) (patterned magnetic media), and the fabrication and commercial future of QMDs. The invention and development of QMDs and nanoimprint are intertwined, and this history is briefly discussed. The chapter is primarily based on author's own research in the field in the last 16 years.
Ultrafast Magnetodynamics with Lateral Resolution: A View by Photoemission Microscopy
Authors: Dürr Hermann A. , Schneider Claus M. 
Published: December 2007

AbstractThe rapidly increasing information density required of modern magnetic data storage devices raises the question of the fundamental limits in bit size and writing speed. Magnetic‐field‐induced magnetization reversal down to picosecond timescales depends on magnetic pulse shape and strength as well as on the sample magnetic properties and dimensions. Optical control of magnetization dynamics is possible on a subpicosecond timescale. This chapter gives an overview of how the combination of magnetic microscopy with lateral resolution down to ∼10 nm and synchrotron/laser light sources with pulses ranging form 50–0.1 ps can address the relevant dynamical processes in magnetic materials.
Soft Magnetic Bulk Glassy and Bulk Nanocrystalline Alloys
Authors: Inoue Akihisa , Makino Akihiro , Bitoh Teruo 
Published: December 2007

Abstract
Soft magnetic bulk glassy alloys have been synthesized in a variety of alloy systems by the copper mold casting process for 10 years since 1995. Their typical alloy systems are classified into five groups, that is (i) Fe(Al, Ga)metalloid, Fe(Cr, Mo)Gametalloid, and FeGametalloid, (ii) (Fe, Co)(Zr, Hf, Nb, Ta)B, (iii) (Fe, C)LnB, (iv) Fe(Cr, Mo, W)CB, and (v) (Fe, Co)BSi(Zr, Nb). The Fe‐ and Co‐based soft magnetic glassy alloys exhibit a large supercooled liquid region beyond 50 K before crystallization. The bulk glassy alloys have been produced in a thickness range of up to 6 mm by the copper mold casting method. In addition, the application of the consolidation technique using the viscous flow phenomenon of the Fe(Al, Ga)metalloid alloys caused the formation of fully dense bulk glassy alloys (BGAs) with rather good soft magnetic properties. The combination of good soft magnetic properties, high glass‐forming ability (GFA), and good workability into a bulk form holds promise for future development as a new type of soft magnetic material.
Rare‐earth Transition‐metal Magnets
Authors: Rodewald Werner 
Published: December 2007

AbstractMost of the SmCo or NdFeB magnets are produced by powder metallurgy in a large variety of shapes. The basic production processes and their impact on the magnetic properties are reported. Alternative production routes and the achieved magnetic properties are reviewed.The magnetization of rare‐earth transition‐metal (RE–TM) magnets and the different coercivity mechanisms are presented in order to assist in proper application.Commercial NdFeB magnets can be operated at temperatures up to 230 °C. Owing to the higher Curie temperatures, sintered SmCo5magnets can be applied up to 250 °C, standard Sm2(Co,Cu,Fe,Zr)17magnets up to 350 °C, and newly developed Sm2(Co,Cu,Fe,Zr)17magnets even up to 550 °C. The basic features, which determine the temperature stability of RE–TM magnets, are discussed in detail.Sometimes, RE–TM magnets need to be operated in hot and humid climates. The RE‐rich constituents of sintered NdFeB magnets are sensitive to corrosion by oxidation and hydrogen embrittlement, which may result in a disintegration of surface layers. The corrosion stability of advanced NdFeB magnets could be improved significantly by replacing corrosion‐sensitive constituents by more noble compounds. In aggressive climates, however, NdFeB magnets need protection by proper coatings. In contrast, SmCo5or Sm2(Co,Cu,Fe,Zr)17magnets hardly suffer any corrosion in hot and humid climates.In applications, sintered magnets may experience mechanical stress. Some mechanical properties of sintered NdFeB magnets, for instance, the compression and the bending strength, the fracture toughness, the Young's modulus, and the Vickers hardness are reviewed, depending on the average grain size.
Superparamagnetic Particles
Authors: Mørup Steen , Hansen Mikkel Fougt 
Published: December 2007

Abstract
The magnetic properties of nanoparticles are reviewed with special emphasis on magnetic relaxation phenomena. After an introduction to superparamagnetic relaxation phenomena, we give a brief introduction to synthesis of nanoparticles and how they can be characterized by standard techniques such as X‐ray diffraction, electron microscopy, and other techniques. We then describe how one can study magnetic relaxation phenomena in noninteracting nanoparticles by different experimental techniques such as DC and AC magnetization measurements, Mössbauer spectroscopy, and neutron scattering. Subsequently, the influence of interparticle interactions on the relaxation is discussed, and it is shown that both magnetic dipole and exchange interactions between nanoparticles can have a significant influence on the relaxation phenomena. Finally, we discuss the magnetic structure in nanoparticles and how spin canting and transverse relaxation can influence the magnetic properties of nanoparticles.
Current Status and Future Development of the Magnetic Materials Industry in China
Authors: Luo Yang 
Published: December 2007

AbstractRecently, the economy in developed countries has got rid of the shadow of recession that took place during the last decade: economic recession in Japan began in the early 1990s, whereas in Europe the recession has not been as strong as expected, and the US economy has been weakened somewhat since the end of 2000. The only exception is China, where the economic boom has continued from the middle of the 1980s with a GDP growth of around 9% per year. These economic developments have had a strong impact on the structure of magnet industries in the world. Owing to the rising cost of manufacturing and a drop in the price of sales, the production of magnets in developed countries has become extremely difficult. As a consequence, western magnet manufacturers produce magnetic assemblies with higher added values, while their magnet production has been partially shifted to developing countries, including China. Product quality in China has been steadily improving during the last decade. From this point of view, Part I of this contribution deals with the macroeconomy aspects of the present and future trends.Part II of this contribution deals with the current status and future trends of the hard magnet industry. Depending on their coercivity or their ability to keep magnetization over long times, magnets are divided into two groups: Soft magnetic materials lose their magnetic moment completely if the applied magnetic field is removed. Hard magnetic materials keep their magnetic moment over many years without applying a magnetic field. Three main types of hard magnetic materials are available: Alnico, hard ferrites, and rare‐earth magnets (SmCo, NdFeB, etc.). Along with the full dense sintered magnets, bonded magnets are also developed in China. Presently, the hard ferrites are the majority of commercially available magnets, but rare‐earth‐based magnets are developing rather fast, both qualitatively and quantitatively. Analyzing the situation of the global magnet industry more deeply and precisely, it turns out that since 1985 the structure of the global magnet industry has changed considerably: Western magnet manufacturers have started to produce downstream devices, such as higher‐valued assemblies, while their magnet production has been reduced or has shifted to developing countries, including China. In Part II, the current status and future trends of the hard magnet industry are reviewed on the basis of statistical data.
Half Metals
Authors: Venkatesan M. 
Published: December 2007

AbstractThe classification of half‐metals is discussed taking account of both itinerant and localized electrons. The recent developments in the search for new half‐metals in oxides, nitrides, sulfides, and Heusler alloys are presented. The different experimental techniques for measuring spin polarization are summarized. The difficulties in measuring the spin polarization directly forced the exploration of other experimental techniques to identify a half‐metal, apart from an integral spin moment, metallic conduction criteria, and band‐structure calculations. The effect of surface/interface states on half‐metallicity is reviewed as the challenges remain in controlling the composition, defects, atomic ordering both in the bulk and at the interface. The possible applications of half‐metals, ideal sources of spin‐polarized electrons, in spin electronics are outlined.
Magnetism and Quantum Criticality in Heavy‐Fermion Compounds: Interplay with Superconductivity
Authors: Stockert Oliver , Nicklas Michael , Thalmeier Peter , Gegenwart Philipp , Steglich Frank 
Published: December 2007

AbstractThe physics of heavy‐fermion compounds is reviewed with a special emphasis on systems located in the vicinity of quantum critical points (QCPs). After a brief introduction into the basic concepts of QCPs, this chapter mainly focuses on the experimental situation in some prototypal heavy‐fermion systems. The discussion of CeCu2Si2and CeTIn5 (T = Co, Ir, Rh), which can be described within aconventionalpicture of a QCP, is followed by a review of theoretical aspects of the different observed behavior at QCPs. However, several systems do not follow this conventional picture of a QCP, but exhibitunconventionalbehavior which is exemplified on one important member, YbRh2Si2. The experimental data are compared with existing theories.
Semiconductor Spintronic Devices
Authors: Flatté Michael E. 
Published: December 2007

Abstract
The sensitivity of semiconductor materials to external perturbations extends to their magnetic properties and other spin‐dependent behavior. Dilute magnetic dopants interact via the carriers in carrier‐mediated ferromagnetic semiconductors, so reducing the carrier concentration with a gate voltage can alter the magnetic properties of these materials. The spin orientation of carriers can change in response to their motion, leading to gate‐controlled spin lifetimes and optical coupling to spin. Semiconductors also offer the potential for nonlinear spin‐dependent transport, particularly at junctions between materials with different magnetizations. These unusual fundamental properties may lead to novel magneto‐optical and magnetoelectronic devices, including magnetic analogs to conventional transistors.