Binary Spin Research Articles

Model of two systems with random P-spin interaction and a fixed correlation between their spin configurations

The binary spins of each subsystem interact within the confines of its subsystem. The scalar product (coupling) of the spin configurations of the two subsystems is fixed. Nontrivial interference develops between the subsystems when (for certain values of the parameters) they can only slide into the spin-glass phase.

Binary-oscillator networks: bridging a gap between experimental and abstract modeling of neural networks.

This paper proposes a simplified oscillator model, called binary-oscillator, and develops a class of neural network models having binary-oscillators as basic units. The binary-oscillator has a binary dynamic variable v = +/- 1 modeling the "membrane potential" of a neuron, and due to the presence of a "slow current" (as in a classical relaxation-oscillator) it can oscillate between two states. The purpose of the simplification is to enable abstract algorithmic study on the dynamics of oscillator networks. A binary-oscillator network is formally analogous to a system of stochastic binary spins (atomic magnets) in statistical mechanics.

Postaccretion magnetic field evolution of neutron stars

We present the first calculations of magnetic field evolution following accretion-induced field reduction which demonstrate the possibility of subsequent surface magnetic field growth. Assuming the preaccretion field is pushed down or advected below the accreting material, we show that significant diffusion of the suppressed field back to the surface can occur within a Galactic age approximately 10(exp 10) yr. This produces surface fields characteristic of standard pulsars if the total mass transferred is below a critical value delta M(sub c) approximately 0.04 solar masses. We then show how this provides a natural explanation for the existence of old pulsars with high inferred surface dipole fields which are still observable. Using our results in conjunction with a model for accretion-induced field reduction we predict the evolution of a binary pulsar's spin and magnetic field through its postaccretion lifetime. This analysis also provides a qualitative explanation for a recent suggestion that the magnetic fields and spins of recycled pulsars have a bimodal distribution.

NOVEL BINARY SPIN GLASS ALLOYS SYNTHESIZED BY MECHANICAL MILLING

A few novel binary spin glass alloys have been successfully synthesized by mechanical milling of ordered intermetallic compounds in a high energy ball mill. These alloys are amorphous Co 2 Ge , atomically disordered crystalline GdAl 2, and ball-milled crystalline and amorphous CoZr. The characteristic features of spin glasses are observed; these are (a) the sharp cusps at the freezing temperature T f in both ac and dc magnetic susceptibility versus temperature curves and their peculiar sensitivity to the external magnetic field; (b) the irreversibility, i.e. the difference in value and shape between the magnetisation versus temperature curves after zero field cooling (ZFC) and field cooling (FC) at temperatures below T f and (c) the displacement of the FC magnetisation curve relative to ZFC curve and the corresponding remanence in the FC curve at low temperatures. The freezing temperatures are 41, 65, 35, and 11 K, respectively, which are defined by the sharp cusps in the lowest field ac susceptibility versus temperature curves. The freezing temperatures are lowered with increasing external field. The common feature of these materials is that all are binary alloys with a rather high concentration of the magnetic component. The discovery of these novel spin glasses is of significance because they not only represent new classes of spin glass materials but also demonstrate the use of mechanical milling as a novel technique to synthesize various new materials such as spin glasses. The results are reviewed briefly.

Influence of Mechanical Milling on Magnetic Properties of Intermetallic Compounds (<I>Overview</I>)

The influence of mechanical milling on magnetic properties of various types of intermetallic compounds has been extensively investigated. It is established that, on the one hand the measurement of magnetic properties is a very sensitive probe to monitor the structural changes of intermetallic compounds during milling, and on the other hand milling may induce in the material unusual and interesting magnetic properties. The results are reviewed. It is generally observed that mechanical milling of an intermetallic compound results in atomic disorder. The disordered materials may remain in the same crystal structure or transform to a different structure, which can be the amorphous structure, a solid solution or a different complex crystalline structure. If the material is crystalline, it becomes always nanocrystalline. The magnetization of various intermetallic compounds after milling was measured at 4.2 K in the Amsterdam High Field Installation in fields up to 21 or 35 T. The high-field magnetization at 4.2 K and the magnetic susceptibility changes usually significantly and sometimes drastically as a consequence of atomic disorder and/or disorder-induced phase transformation. The magnetic ordering temperature was also measured in some compounds. The obtained results turn out to provide precise information about the structural change of a compound in particular during the intermediate stage of milling. Upon disordering or phase transformation, the nature of the magnetic ordering of a compound can be markedly different from its ordered form. This is illustrated by the discovery of two novel binary concentrated spin glasses namely amorphous Co2Ge and atomically disordered crystalline GdAl2.

Selective saturation in magnetization transfer experiments.

The concept of magnetic saturation in single and binary spin systems is essential to the understanding of magnetization transfer experiments. This paper outlines the requirements for selective magnetic saturation of either of two spin pools contained in a mixture, both having identical chemical shifts. Following a brief discussion of saturation in a homogeneous sample, simple relationships are derived that predict the maximum degree of selective saturation in a two-spin nonexchanging system. Optimal saturation conditions are described in terms of the intrinsic relaxation parameters as well as the experimental conditions of saturation offset frequency and amplitude. In addition, a novel method is proposed that may be applied to saturate the "free" water as opposed to the "bound" water spins in a magnetization transfer experiment. Saturation in an exchanging system is well approximated by these relationships under some physiologically relevant conditions, examples of which are provided. Application of the relationships presented may be useful in the design of experiments to produce maximum magnetization transfer contrast.

Spin filtering processes and automatic extraction of fringe centerlines in digitial interferometric patterns

Two filtering algorithms-spin filter and binary spin filter-suitable for various digital interferometric images are presented in this paper. Both can filter out the noise in the interferometric patterns without distorting the fringe features, whereas other commonly used filters, such as median filter and FFT passband filter, may blur the patterns. A process for automatically extracting fringe centerlines all over the field is also proposed. This is done by using the spin filters mentioned above together with the derivative binary image. The effectiveness of this technique is illustrated experimentally.