Study of ferromagnetic bulk domains by neutron depolarization in three dimensions

The polarization change of a polarized neutron beam after transmission through a partly magnetized ferromagnetic material can be described by a (3×3) depolarization matrix. A theory has been developed to interpret this matrix in terms of well-known magnetic domain quantities such as the reduced mean magnetizationm, the mean domain size δ and the mean square direction cosines γ _x , γ _y and γ _z of the inner magnetization within the domains. In order to do this it was necessary to make some simplifying assumptions about ferromagnetic domain structures. The influences of these assumptions on the quantities derived have been discussed. Finally the theory has been applied to depolarization measurements in nickel foils with the magnetic field and mechanical stress as parameters.     

Stability of symmetries for equilibrium configurations ofN particles in three dimensions

We consider equilibrium configurations ofn identical particles in three dimensions interacting via two-body potentials depending only on the distance. The symmetry group of a given configuration is defined as the subgroup of isometries which leaves it invariant, up to permutations of the particles. We prove the stability of the symmetry in the following sense: the symmetry group of an equilibrium configuration is the same for the neighboring equilibria arising from any small enough perturbation of the initial potential. Furthermore, for a large class of realistic potentials, the existence of nontrivial symmetries is proved, thus giving a completely geometrical, although partial, approach to the classical crystal problem.     

First order phase transition in the plane rotator ferromagnetic model in two dimensions

We show that the two-dimensional isotropic ferromagnetic rotator model exhibits a first order phase transition if the interaction decays asr ^– with 2<<4.Work supported by Fonds National Suisse de la Recherche Scientifique.     

Analytical properties and exact solutions of static plasma equilibrium systems in three dimensions

For static reductions of isotropic and anisotropic magnetohydrodynamics plasma equilibrium models, a complete classification of admitted point symmetries and conservation laws up to first order is presented. It is shown that the symmetry algebra for the isotropic equations is finite-dimensional, whereas anisotropic equations admit infinite symmetries depending on a free function defined on the set of magnetic surfaces. A direct transformation is established between isotropic and anisotropic equations, which provides an efficient way of constructing new exact anisotropic solutions. In particular, axially and helically symmetric anisotropic plasma equilibria arise from classical Grad-Shafranov and JFKO equations.     

Fresnel particle tracing in three dimensions using diffraction phase microscopy

We have developed a novel experimental technique for tracking small particles in three dimensions with nanometer accuracy. The longitudinal positioning of a micrometer-sized particle is determined by using the Fresnel approximation to describe the transverse distribution of the wavefront that originated in the particle. The method utilizes the high-sensitivity quantitative phase imaging capability of diffraction phase microscopy recently developed in our laboratory. We demonstrate the principle of the technique with experiments on Brownian particles jittering in water both in bulk and in the vicinity of a boundary. The particles are localized in space within an error cube of 20 nm x 20 nm x 20 nm for a 33 Hz acquisition rate and 20s recording time.     

First-order phase transition and phase coexistence in a spin-glass model

We study the mean-field static solution of the Blume-Emery-Griffiths-Capel model with quenched disorder, an Ising-spin lattice gas with random magnetic interaction. The thermodynamics is worked out in the full replica symmetry breaking scheme. The model exhibits a high temperature/low density paramagnetic phase. As temperature decreases or density increases, a phase transition to a full replica symmetry breaking spin-glass phase occurs. The nature of the transition can be either of the second order or, at temperature below a given critical value, of the first order in the Ehrenfest sense, with a discontinuous jump of the order parameter, a latent heat, and coexistence of phases.     

Absence of crystalline ordering in two dimensions

We give conditions on the potential of a classical particle system, which imply absence of crystalline ordering in two dimensions. We thereby correct and extent some results in a previous paper.J. Fröhlich: Comment on Absence of Crystalline Ordering in two Dimensions     

Transitions between spin-glass and ferromagnetic (or related) states in disordered Ni-Mn alloys

Magnetic measurements reveal that the alloy Ni₇₈Mn₂₂ undergoes a field-induced spin-glass-to-ferromagnetic transition at a critical field that decreases from ≈ 140 Oe to zero as the temperature is raised from 4.2 to 40 K, its ferromagnetic Curie point being ≈ 270 K. The alloy Ni₇₄Mn₂₆ is found to have a related state of infinite initial susceptibility but no spontaneous magnetization between ≈ 80 and ≈ 155 K. Below 40 and 80 K, respectively, Ni₇₈Mn₂₂ and Ni₇₈Mn₂₂ exhibit the thermoremanent properties of a spin glass.     

Absence of a “ferromagnet-spin glass” reentrant phase transition in quasi-two-dimensional ferromagnetic systems with competing exchange interactions

It is shown on the basis of the results of magnetic investigations for the example of the intercalated layered compounds Cr_1/3−x Ni_xTaS₂ that in quasi-two-dimensional ferromagnets with competing exchange interactions there is no reentrant “ferromagnet-spin glass” phase transition all the way down to liquid-helium temperatures. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 155–158 (25 January 1997)     

Nature of the transition between a ferromagnetic metal and a spin-glass insulator in pyrochlore molybdates

The metal-insulator transition has been investigated for pyrochlore molybdates R(2)Mo(2)O(7) with nonmagnetic rare-earth ions R. The dynamical scaling analysis of ac susceptibility reveals that the geometrical frustration causes the atomic spin-glass state. The reentrant spin-glass phase exists below the ferromagnetic transition. The electronic specific heat is enhanced as compared to the band calculation result, perhaps due to the orbital fluctuation in the half-metallic ferromagnetic state. The large specific heat is rather reduced upon the transition, likely because the short-range antiferromagnetic fluctuation shrinks the Fermi surface.     

Diffraction in three dimensions

Atmospheric Convection . By K. A. Emanuel. 1994, £47.50 (hbk), pp. x+580. Oxford, ISBN 0 19 506630 8. Scope: text. Level: postgraduate.

Automotive Sensors . By M. H. Westbrook and J. D. Turner. 1994, £75.00, US$149.00 (hbk), pp. xviii + 253. IOP, ISBN 0 7903 0293 3. Scope: monograph. Level: specialist.

Computation in Modem Physics . By W. R. Gibbs. 1994, £38.00 (hbk), pp. xvii + 348. World Scientific, ISBN 981 02 2044 8. Scope: text. Level: undergraduate and postgraduate.

Electron Correlations in Molecules and Solids , 2nd Edn. By P. Fulde. 1993, DM78.00 (pbk), pp. xiv + 422. Springer-Verlag, ISBN 3 540 56376 8. Scope: monograph. Level: postgraduate and specialist.

Field Theory, A Path Integral Approach . By A. Das. 1994, £48.00 (hbk), pp. xv + 399. World Scientific, ISBN 981 02 1396 4. Scope: lecture notes. Level: postgraduate.

Infrared Technology Fundamentals , 2nd Edn, revised and expanded. By M. Schlessinger. 1994, US$125.00 (hbk), pp. xii + 462. Dekker, ISBN 0 8247 9259 9. Scope: monograph. Level: postgraduate and specialist.

Oceanography and Acoustics . Edited by A. R. Robinson and D. Lee. 1994, US$65.00 (hbk), pp. xvii + 257. AIP, ISBN 1 56396 203 9. Scope: multi-author review. Level: postgraduate and specialist.

Optoelectronic Integration: Physics, Technology and Applications . Edited by O. Wada. 1994, Dfl. 275.00, US$130.00, £96.25 (hbk), pp. x + 458. Kluwer, ISBN 0 7923 9453 4. Scope: multi-author review. Level: postgraduate and specialist.

Photonic Devices and Systems . Edited by R. C. Hunsperger. 1994, US$135.00 (hbk), pp. xi + 426. Dekker, ISBN 0 8247 9243 2. Scope: multi-author review. Level: postgraduate and specialist.

Physics and Our View of the World . Edited by J. Hilgevoord. 1994, US$22.95 (pbk), pp. 304. Cambridge, ISBN 0 521 47680 1. Scope: multi-author review. Level: scientists and philosophers of science.

Polymer Physics . By U.W. Gedde. 1995, £49.00 (hbk), £24.99 (pbk), pp. x + 298. Chapman &; Hall, ISBN 0 412 62640. Scope: textbook. Level: undergraduate and postgraduate.

Quantization of Gauge Systems . By M. Henneaux and C. Teitelboim. 1994, US$29.95, £25.00 (pbk) pp. xxii + 520. Princeton, ISBN 0 691 03769 8. Scope: textbook. Level: postgraduate and specialist.

Semiconductor Raman Lasers . By K. Suto and J.-I. Nlshlzawa. 1994, £63.00 (hbk), pp. ix + 226. Artech, ISBN 0 89006 667 1. Scope: monograph. Level: specialist.

Shapes and Shells in Nuclear Structure . By S. G. Nilsson and I. Ragnarsson. 1995, £60.00, US$89.95 (hbk), pp. xiv + 408. Cambridge, ISBN 0 521 37377 8. Scope: textbook. Level: postgraduate.

Supersymmetric Gauge Field Theory and String Theory . By D. Bailin and A. Love. 1994, £80.00, US$160.00 (hbk), £27.50, US$49.00 (pbk), pp. xii + 332. IOP, ISBN 0 7503 0268 2. Scope: textbook. Level: postgraduate.

Short notices Advanced Series in Neuroscience , Vol. 3. Biology and Computation, A Physicist's Choice. Reprint volume. Edited by H. Gutfreund and G. Toulouse. 1994, £94.00 (hbk) pp. xv + 852. World Scientific, ISBN 981 02 1405 7. Scope: reprints. Level: postgraduate and specialist.

Electronic Structure of Refractory Carbides and Nitrides . Edited by V. A. Gubanov, A.L. Ivanovsky and V. P. Zhukov. 1994, $79.95 (hbk) pp. xiv + 256. Cambridge University Press, ISBN 0 521 41885 2. Scope: monograph. Level: postgraduate and specialist.

Fritz London: A Scientific Biography . By K. Gavroglu. 1995, £50.00 (hbk), pp. xxiv + 299. Cambridge University Press, ISBN 0 521 43273 1. Scope: biography. Level: general reader.

Gallium Arsenide and Related Compounds 1993 . Edited by H. S. Rupprecht and G. Weinmann. 1994, £115.00, US$230.00 (hbk), pp. xxiv + 842. IOP, ISBN 0 7503 0295 X. Scope: conference proceedings. Level: postgraduate and specialist.

Matvei Petrovich Bronstein and Soviet Physics in the Thirties . By G. E. Gorelik and V. Y. Frenkel. 1994, £65.00, DM 168.00. sFr. 148.00 (hbk), pp. 208. Birkhauser, ISBN 3 7643 2752 9. Scope: biography. Level: non-specialist.

Physical Chemistry . 5th edn. By P. W. Atkins. 1994, £24.00 (pbk), pp. xix + 1145. Oxford, ISBN 0 19 855730 2. Scope textbook. Level: undergraduate.

Polyominoes. Puzzles, Patterns, Problems, and Packings . Revised and expanded 2nd edn. By S.W. Golomb. 1994, US$24.95, £19.95 (hbk) pp. xii + 181. Princeton University Press, ISBN 0 691 08573 0. Scope: text. Level: non-specialist.

Supercollider 5 . Edited by P. Hale. 1994, US$195.00 (hbk), pp. xxviii + 970. Plenum, ISBN 0 306 44705 3. Scope: conference proceedings. Level: postgraduate and specialist.

World Scientific Series in 20th Century Physics , Vol. 5. Selected Papers of Abdus Salam (With Commentary). Edited by A. Ali, C. Isham, T. Kibble and Riazuddin. 1994, £64.00 (hbk) pp. xiv + 679. World Scientific, ISBN 981 02 1662 9. Scope: reprinted papers. Level: specialist.     

Acoustic susceptibility of an insulating spin-glass

High frequency acoustic measurements have been performed at temperatures around the freezing pointT _c in a cobalt insulating spin-glass. Assuming a Waller coupling mechanism between the spins and the acoustic wave, the data are interpreted in the framework of a dynamical model which takes into account the modulation of the reaction field. As a result, at the freezing temperature the characteristic relaxation time has no anomaly while the relevant susceptibility presents a maximum. The peculiar frequency dependence (as ^1/2) atT _c of the complex elastic constant is experimentally put in evidence.Associated with the Centre National de la Recherche Scientifique (UA 789)     

Quantum-mechanically induced asymmetry in the phase diagrams of spin-glass systems

The spin-1/2 quantum Heisenberg spin-glass system is studied in all spatial dimensions d by renormalization-group theory. Strongly asymmetric phase diagrams in temperature and antiferromagnetic bond probability p are obtained in dimensions d>or=3. The asymmetry at high temperatures approaching the pure ferromagnetic and antiferromagnetic systems disappears as d is increased. However, the asymmetry at low but finite temperatures remains in all dimensions, with the antiferromagnetic phase receding from the ferromagnetic phase. A finite-temperature second-order phase boundary directly between the ferromagnetic and antiferromagnetic phases occurs in d>or=6, resulting in a new multicritical point. In d=3, 4, 5, a paramagnetic phase reaching zero temperature intervenes asymmetrically between the ferromagnetic and reentrant antiferromagnetic phases. There is no spin-glass phase in any dimension.