Theoretical results concerning the influence of non‐random‐field defects

We shall focus on extended defect systems and review their critical behavior. Primarily, with two aims, one of which is to understand phase transitions and how to derive effective dimension of extended defects with various structures, and the other is to propose a new research-method for defect systems, we let extended defects grow on a triangular lattice with frustration in a similar fashion to diffusion-limited aggregation, and discuss the situation. The existence of phase transitions, phase diagram, effective defect dimension, etc. will be shown. Furthermore, we shall summarize theoretical studies of extended defect systems on phase diagrams, critical behavior, tricritical behavior, and crossover behavior as static properties, and on nonconserved systems and conserved systems as dynamic properties.     

A study of magnetism in disordered Pt-Mn, Pd-Mn and Ni-Mn alloys: an augmented space recursion approach

In this paper we shall study three binary alloy systems, one constituent of which is Mn. The other constituents are chosen from a particular column of the periodic table: Ni(3d), Pt (4d) and Pd (5d). As we go down the column, the d-bands become wider, discouraging spin-polarization. In a disordered alloy, the situation becomes more complicated, as the exchange interaction between two atoms is environment dependent. We shall compare and contrast their magnetic behaviour using robust electronic structure techniques. In all three alloy systems conjectures are made to explain experimental data. In this paper we shall examine whether there is any basis to these conjectures.     

Biological nanophase magnetic materials

Biological systems provide a number of examples of magnetic materials in which key structural features are in the nanometre size range. These can be used as model systems for investigations of their magnetic behaviour or they can provide a source of novel magnetic materials. Both of these aspects will be considered in this review, with particular reference to the use of Mössbauer spectroscopy as a technique for both characterisation and magnetic investigation.     

Theoretical determination of the magnetic properties of 2-pyrone and 4-pyrone,and o-benzoquinone and p-benzoquinone

A series of theoretical procedures, relying on the conventional common-origin and distributed-origin approaches, and adopting extended gaugeless as well as London basis sets, have been applied at the Hartree-Fock level of accuracy to predict magnetic susceptibilities and nuclear magnetic shieldings of four molecular systems that aroused particular interest and discussion concerning their aromatic character. The theoretical results are of near Hartree-Fock quality. Comparison with experimental values for magnetic susceptibilities seems to indicate that the latter need to be revised. Analysis of calculated properties and of plots of current density induced by the magnetic field in the π-electrons provides simple and effective tools for the classification of 2- and 4-pyrones, and o- and p-benzoquinone as non-aromatic.     

Asymmetrical shapes of optical line profiles in individual quantum dots

The experimental data on individual quantum dots show that the optical line can have the form of a very narrow spike accompanied by a shoulder. So far the shoulder has been found at the lower energy side of the narrow peak. In the present work, we study theoretically the origin of such a lineshape. We shall use a simple model of quantum dot and a simple approximation to the electronic excitation. The electronic system will be assumed to be coupled to the longitudinal optical phonons. We will show that the electronic multiple scattering on the optical phonons can then give us an explanation of the observed optical lineshape.     

Spin glasses: Some recent experiments

This review of the spin-glass problem will begin by considering the basic ingredients of a spin glass. Then I shall summarize the fundamental experimental properties and the real systems which are being studied. A bit of theory will be presented to show how idealized the models are when compared to the real materials. Finally I shall discuss the dynamics of the spin-glass phase transition and relaxations within the frozen state, drawing upon the muon investigations wherever possible.     

Dipole-dipole minimum energy configuration for Platonic,Archimedean and Catalan solid structures

Several magnetic materials consisting of dipoles owe their properties to the specific nature of the dipole-dipole interaction. In the present work, we study systems of dipoles where the particles are arranged on various types of three-dimensional structures. However, these solids are not arbitrary. They constitute the well-known Platonic, Archimedean and Catalan solids. We systematically study them in order to fill a gap in the literature that does not contemplate this interaction in the previous solids, despite the fact that they are encountered in many different physical systems. In particular, in the regime of strong dipole moments where a classical treatment is possible, we shall provide not only the minimum energy but also the precise orientations of all their dipoles. We will numerically obtain the minimum energy configuration where all vertices possess the same classic dipole, either electric or magnetic.     

Modeling phase behavior for quantifying micro-pervaporation experiments

We present a theoretical model for the evolution of mixture concentrations in a micro-pervaporation device, similar to those recently presented experimentally. The described device makes use of the pervaporation of water through a thin PDMS membrane to build up a solute concentration profile inside a long microfluidic channel. We simplify the evolution of this profile in binary mixtures to a one-dimensional model which comprises two concentration-dependent coefficients. The model then provides a link between directly accessible experimental observations, such as the widths of dense phases or their growth velocity, and the underlying chemical potentials and phenomenological coefficients. It shall thus be useful for quantifying the thermodynamic and dynamic properties of dilute and dense binary mixtures.     

Theory of origin of hyperfine interactions in atomic systems

We shall review recent developments in the theory of magnetic hyperfine interactions, including the influence of many-body and relativistic effects and the finite spreads of nuclear charge and magnetic moment distributions. The present status of the understanding of these effects will be illustrated by analyzing a number of different systems including the alkali atoms, alkaline earth ions and several half-filled shell atomic and ionic systems.     

A concise review of Rydberg atom based quantum computation and quantum simulation

Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago.Recent experimental and theoretical progresses have shined exciting light on this avenue.In this concise review,we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation.We shall also include related discussions on quantum optics with Rydberg atomic ensembles,which are increasingly used to explore quantum computation and quantum simulation with photons.     

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems.In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given.In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.     

Convection driven zonal flows and vortices in the major planets

The dynamical properties of convection in rotating cylindrical annuli and spherical shells are reviewed. Simple theoretical models and experimental simulations of planetary convection through the use of the centrifugal force in the laboratory are emphasized. The model of columnar convection in a cylindrical annulus not only serves as a guide to the dynamical properties of convection in rotating sphere; it also is of interest as a basic physical system that exhibits several dynamical properties in their most simple form. The generation of zonal mean flows is discussed in some detail and examples of recent numerical computations are presented. The exploration of the parameter space for the annulus model is not yet complete and the theoretical exploration of convection in rotating spheres is still in the beginning phase. Quantitative comparisons with the observations of the dynamics of planetary atmospheres will have to await the consideration in the models of the effects of magnetic fields and the deviations from the Boussinesq approximation.     

Spin–orbit induced magnetic phenomena in bulk metals and their surfaces and interfaces

First-principles electronic structure studies based on local spin density functional theory and performed on extremely complex simulations of ever increasingly realistic systems, play a very important role in explaining and predicting surface and interface magnetism. This review deals with what is a major issue for first-principles theory, namely the theoretical/computational treatment of the weak spin–orbit coupling in magnetic transition metals and their alloys and its important physical consequences: magneto-crystalline anisotropy, magnetostriction, magneto-optical Kerr effects and X-ray magnetic circular dichroism. As is demonstrated, extensive first-principles calculations and model analyses now provide simple physical insights and guidelines to search for new magnetic recording and sensor materials.     

Superferromagnetic nanostructures

Interactions between magnetic nanoparticles can lead to superferromagnetic ordering, i.e. ordering of their magnetic moments at low temperatures. The use of a simple mean field theory, describing the temperature dependence of the order parameter is discussed. This model is found to give excellent fits to experimental results. In systems of particles with pure dipole interactions, the degree of ordering depends critically on the geometrical configuration of the particles. The application of superferromagnetic nanostructures for magnetic refrigeration is also discussed.     

Detection and study of magnetic micro-and nanostructures using dark-field optical microscopy

The features of magnetic-microstructure imaging were studied using various configurations of dark-field magnetooptical microscopy. The potentials and limitations of the dark-field method were experimentally and theoretically analyzed as applied to magnetism studies. The experimental data showed the possibility of magnetooptical detection of localized magnetic structures of size smaller than or of the order of 0.1 μm. To calculate the angular spectrum of light scattered at magnetic inhomogeneities within a theoretical model, the method of electrodynamic tensor Green functions was employed. Within the theoretical model, a procedure was proposed and analyzed which allows real-time visualization of magnetization reversal of solitary single-domain nanoparticles or their regular arrays in order to study their dynamic and static characteristics. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 3, 2003, pp. 490–499. Original Russian Text Copyright ? 2003 by Belotelov, Logginov, Nikolaev.     

Proposed spin amplification for magnetic sensors employing crystal defects

Recently there have been several theoretical and experimental studies of the prospects for magnetic field sensors based on crystal defects, especially nitrogen vacancy (NV) centers in diamond. Such systems could potentially be incorporated into an atomic force microscopy-like apparatus in order to map the magnetic properties of a surface at the single spin level. In this Letter we propose an augmented sensor consisting of an NV center for readout and an "amplifier" spin system that directly senses the local magnetic field. Our calculations show that this hybrid structure has the potential to detect magnetic moments with a sensitivity and spatial resolution far beyond that of a simple NV center, and indeed this may be the physical limit for sensors of this class.