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See detailMagnetic confinement of the superconducting condensate in superconductor-ferromagnet hybrid composites
Gillijns, W.; Aladyshkin, A Yu; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2007), 76(6),

The influence of an inhomogeneous magnetic field on the magnetoresistance of thin Al films, used in different superconductor-ferromagnet hybrids, has been investigated. Two contrasting magnetic textures ... [more ▼]

The influence of an inhomogeneous magnetic field on the magnetoresistance of thin Al films, used in different superconductor-ferromagnet hybrids, has been investigated. Two contrasting magnetic textures with out-of-plane magnetization are explored: namely, (i) a plain film in a multidomain state and (ii) an array of microsized dots. The stray fields of the ferromagnetic structures confine the superconducting condensate and, accordingly, modify the condition for the nucleation of superconductivity. By switching between different magnetic states of the ferromagnet, this confinement can be tuned at will, thereby reversibly changing the dependence of the critical temperature T-c on an external magnetic field H. In particular, continuous evolution from a conventional linear T-c(H) dependence with a single maximum to a reentrant superconducting phase boundary with multiple T-c peaks has been demonstrated. [less ▲]

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See detailMagnetic diffusion-limited aggregation
Vandewalle, Nicolas ULg; Ausloos, Marcel ULg

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (1995), 51(1), 597-603

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See detailMagnetic Eden model
Ausloos, Marcel ULg; Vandewalle, Nicolas ULg; Cloots, Rudi ULg

in Europhysics Letters [=EPL] (1993), 24(8), 629-634

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is ... [more ▼]

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is controlled by a condition depending on the <<magnetic state>> of the perimeter (through some <<spin coupling>>) and an external parameter, the <<magnetic field>>. Even though these words seem to refer to some <<energetic condition>> the growth model is of purely kinetic origin. This is demonstrated by exactly solving the 1-dimensional growth model for a semi-open chain, and, e.g. finding the correlation functions. In two-dimensions, simulations of clusters lead us to show that the perimeter growth exponent is coupling dependent. We show the morphologies of growth clusters on a <<phase diagram>> and indicate the <<physical origin>> and transition(s) between compact and lacunar clusters. [less ▲]

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See detailMagnetic fabrics in jotunite dykes from the Late-Proterozoic Rogaland anorthosite province (SW Norway)
Bolle, Olivier ULg; Besse, Michal; Diot, Hervé

in Geophysical Research Abstracts (2005), 7

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See detailMagnetic fabrics in the Holum granite (Vest-Agder, southernmost Norway): implications for the late evolution of the Sveconorwegian (Grenvillian) orogen of SW Scandinavia
Bolle, Olivier ULg; Diot, Hervé; Trindade, Ricardo I.F.

in Precambrian Research (2003), 121(3-4), 221-249

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See detailMagnetic field studies of massive main sequence stars
Schöller, M.; Hubrig, S.; Ilyin, I. et al

in American Institute of Physics Conference Series (2012, May 01)

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars ... [more ▼]

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, β Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, and stellar winds. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation periods and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications for the stellar physical parameters and evolution. [less ▲]

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See detailMagnetic field studies of massive main sequence stars
Schöller, M.; Hubrig, S.; Ilyin, I. et al

in Astronomische Nachrichten (2011), 332

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars ... [more ▼]

We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, β Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution. [less ▲]

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See detailMagnetic fields in beta Cep, SPB, and Be stars
Schoeller, M.; Hubrig, S.; Briquet, Maryline ULg et al

in Proceedings of the Conference: "Putting A Stars into Context: Evolution, Environment, and Related Stars" (2013, September 01)

Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric ... [more ▼]

Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric behavior, the upper main-sequence B-type stars are assigned to different groups, such as beta Cep stars and slowly pulsating B (SPB) stars, He-rich and He-deficient Bp stars, Be stars, BpSi stars, HgMn stars, or normal B-type stars. All these groups are characterized by different magnetic field geometry and strength, from fields below the detection limit of a few Gauss up to tens of kG. Our collaboration was the first to systematically study the magnetic fields in representative samples of different types of main-sequence B stars. In this article, we give an overview about what we have learned during the last years about magnetic fields in beta Cep, SPB, and Be stars. [less ▲]

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See detailMagnetic fields in massive stars
Hubrig, S.; Scholler, M.; Briquet, Maryline ULg et al

in Contributions of the Astronomical Observatory Skalnaté Pleso (2008), 38

We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

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See detailMagnetic fields in O stars
Nazé, Yaël ULg

in Mathys, Gauthier; Griffin, E.; Kochukhov, O. (Eds.) et al proceedings of "Putting A-stars into context" (2014, November 01)

Over the last decade, large-scale, organized (generally dipolar) magnetic fields with a strength between 0.1 and 20 kG were detected in dozens of OB stars. This contribution reviews the impact of such ... [more ▼]

Over the last decade, large-scale, organized (generally dipolar) magnetic fields with a strength between 0.1 and 20 kG were detected in dozens of OB stars. This contribution reviews the impact of such magnetic fields on the stellar winds of O-stars, with emphasis on variability and X-ray emission. [less ▲]

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See detailMagnetic fields in O-, B- and A-type stars on the main sequence
Briquet, Maryline ULg

in European Physical Journal Web of Conferences (2015, September 01)

In this review, the latest observational results on magnetic fields in main-sequence stars with radiative envelopes are summarised together with the theoretical works aimed at explaining them.

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See detailMagnetic fields of HgMn stars
Hubrig, S.; González, J. F.; Ilyin, I. et al

in Astronomy and Astrophysics (2012), 547

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of ... [more ▼]

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15 G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. <BR /> Aims: We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system AR Aur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. <BR /> Methods: We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. <BR /> Results: Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars as well as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars. Based on observations obtained at the European Southern Observatory (ESO programmes 076.D-0169(A), 076.D-0172(A), 084.D-0338(A), 085.D-0296(A), 085.D-0296(B), 087.D-0049(A), 088.D-0284(A)), SOFIN observations at the 2.56 m Nordic Optical Telescope on La Palma, and observations obtained with the CORALIE Echelle Spectrograph on the 1.2 m Euler Swiss telescope on La Silla, Chile.Tables 2-7, 9, 10 are only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailMagnetic Fields of Hot Pulsating Stars
Hubrig, S.; Ilyin, I.; Schöller, M. et al

in Magnetic Stars. Proceedings of the International Conference, held in the Special Astrophysical Observatory of the Russian AS, August 27- September 1, 2010, Eds: I. I. Romanyuk and D. O. Kudryavtsev (2011)

In spite of recent detections of magnetic fields in a number of β Cephei and slowly pulsating B (SPB) stars, their impact on stellar rotation, pulsations, and element diffusion is not sufficiently studied ... [more ▼]

In spite of recent detections of magnetic fields in a number of β Cephei and slowly pulsating B (SPB) stars, their impact on stellar rotation, pulsations, and element diffusion is not sufficiently studied yet. One reason for this is the lack of knowledge of rotation periods, magnetic field strength distribution and temporal variability, and field geometry. New longitudinal field measurements of four β Cephei and candidate β Cephei stars, and two SPB stars were acquired with the FORS2 at the VLT. These measurements allowed us to carry out a search for rotation periods and to constrain magnetic field geometry for a few stars in our sample. [less ▲]

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See detailMagnetic Flux Closure Directly Induced by Interplanetary Shocks: Observations Using IMAGE-FUV and SuperDARN, and Modelling With GUMICS-4.
Hubert, Benoît ULg; Palmroth, M.; Milan, S. E. et al

Conference (2005, December 01)

A method has been developed to monitor the dayside and nightside reconnection rates using FUV remote sensing of the proton aurora and ionospheric convection patterns. Global images of the proton aurora ... [more ▼]

A method has been developed to monitor the dayside and nightside reconnection rates using FUV remote sensing of the proton aurora and ionospheric convection patterns. Global images of the proton aurora are obtained using the SI12 instrument of the FUV experiment on board the IMAGE satellite, and used to identify the open/closed (o/c) field line boundary. SuperDARN data are used to determine the ionospheric convection velocity, and the associated electric field. The dayside and nightside reconnection voltages are then determined accounting for the ionospheric electric field and the motion of the o/c boundary. This method is used to compute the dayside and nightside reconnection voltages during two interplanetary shocks for which the IMF was mostly northward, so that the amount of open magnetic flux was so small that no significant substorm expansion phase could develop. The flux closure voltage shows a sharp signature when the interplanetary shocks sweep by the nightside magnetosphere. MHD simulations conducted using the GUMICS-4 model for similar conditions show a similar signature in the nightside flux closure rate. We suggest that this flux closure event is directly induced by the compression of the magnetotail. [less ▲]

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See detailMagnetic flux distribution and hysteresis properties of bulk high temperature ferromagnet / superconductor / ferromagnet hybrid structures
Philippe, Matthieu ULg; Ainslie, Mark D; Fagnard, Jean-François ULg et al

Poster (2014, August)

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings where their large flux density / volume ... [more ▼]

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings where their large flux density / volume ratio makes them more efficient than traditional ferromagnetic permanent magnets. However, the magnetic flux distribution above a bulk HTS magnet is strongly non-uniform (conic profile predicted by the Bean model) and influenced by the finite length of the superconductor (curvature of the flux lines through the volume of the superconductor). In the present work, we study how ferromagnetic materials can be combined with a bulk, large grain YBCO superconductor to improve the average value of the magnetic induction through the volume of the superconductor and to shape the magnetic induction at the surface. Various pieces of different shapes were machined in two high permeability ferromagnetic alloys with different saturation magnetizations (0.8 T and 1.4 T). These pieces were placed on (i) the top surface of the bulk HTS cylinder to form bulk ferromagnet / superconductor (F/S) hybrid structures and (ii) the top and bottom surfaces to form bulk F/S/F structures. The magnetic properties of each hybrid structure subjected to an axial magnetic field were measured at 77 K. Pick-up coils were used to measure the average magnetic induction inside the superconductor and miniature Hall probes were used to map the remanent induction near the top and bottom surfaces of the assemblies. The modifications of the hysteresis curves and flux distributions were examined taking into account that flux lines are trapped by the ferromagnetic component, which drives the return flux lines towards the outside of the superconductor. The superconductor hysteresis curve can be analysed as a combination of a diamagnetic and a ferromagnetic behaviour depending on the ferromagnet intrinsic properties (intrinsic permeability, saturation) and geometrical properties (size and volume). The bulk average remanent magnetization increases in presence of the ferromagnets (F/S/F structures give the best results) and is only slightly dependent on the saturation magnetization. When the ferromagnet is fully saturated, its saturation value dictates the magnetic behaviour of the hybrid structure which shows an addition of the superconductor and ferromagnet magnetic effects. [less ▲]

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See detailMagnetic flux patterns in superconductors deposited on a lattice of magnetic dots: A magneto-optical imaging study
Gheorghe, Diana G; Wijngaarden, Rinke J; Gillijns, Werner et al

in Physical Review. B : Condensed Matter (2008), 77(5),

We investigate the flux penetration in Pb films, of different shapes, deposited on top of a periodic array of Co/Pt dots with perpendicular anisotropy by means of magnetization and magneto-optical ... [more ▼]

We investigate the flux penetration in Pb films, of different shapes, deposited on top of a periodic array of Co/Pt dots with perpendicular anisotropy by means of magnetization and magneto-optical measurements. A clear dependence of the critical current density on the magnetic state of the dots and their polarity with respect to the direction of the applied magnetic field is observed by both techniques. The magnetic state of the dots changes the flux penetration from smooth to channelling. Additionally, in the fully magnetized state, an anisotropic current distribution is observed in circular-shaped samples. The flux penetration is dominated by avalanches only for configurations which correspond to a high critical current, irrespective of its origin, be it low temperature, magnetization state of the dots, or angle between the lattice of dots and the edge of the sample. [less ▲]

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See detailMagnetic flux penetration and creep in BSSCO-2223 composite ceramics
Vanderbemden, Philippe ULg; Destombes, Christophe; Cloots, Rudi ULg et al

in Superconductor Science and Technology (1998), 11(1), 94-100

We have experimentally investigated the magnetic flux penetration through a Bi-2223 polycrystalline superconductor synthesized by a classical solid-state reaction method. Electrical resistance, AC ... [more ▼]

We have experimentally investigated the magnetic flux penetration through a Bi-2223 polycrystalline superconductor synthesized by a classical solid-state reaction method. Electrical resistance, AC susceptibility, the Campbell method and magnetic flux waveform recordings have been analysed and compared in order to separate clearly intergrain and intragrain contributions. The AC susceptibility frequency dependence has been also examined at T = 77 K in a broad field range (0.01 G < B-AC < 100 G) The activation energy as a function of AC applied magnetic field is found to present a pronounced minimum for an induction (8 G) corresponding to full magnetic flux penetration through the intergranular matrix. [less ▲]

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