References of "Fagnard, Jean-François"
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See detailExperimental study of the magnetic shielding performances of a Bi2223 tube closed by a Bi2223 cap.
Wera, Laurent ULiege; Fagnard, Jean-François ULiege; Hogan, Kevin ULiege et al

Poster (2014, August 12)

A superconducting tube can be used as an efficient magnetic shield. However, the shielding factor (defined as the ratio between the applied magnetic induction and the magnetic induction measured inside ... [more ▼]

A superconducting tube can be used as an efficient magnetic shield. However, the shielding factor (defined as the ratio between the applied magnetic induction and the magnetic induction measured inside the tube) decreases towards tube extremities because of the field penetration through the open ends of the tube. To improve the performances at tube extremities, the tube should be closed. This can be achieved by using a superconducting vessel or by closing both extremities with a cap. The purpose of the present work is to study experimentally the shielding performances of a Bi2223 tube closed by a superconducting Bi2223 cap. The cap is a circular plate with a diameter equal to the outer diameter of the tube and there is no superconducting joint between the cap and the tube. Our interest is to characterize the effect of the cap on the shielding factor distribution along the tube axis when only one extremity of the tube is closed. We also study the effect of the gap size between the cap and the tube in axial configuration. Finally, a tube closed at its both ends is also characterized. All experiments are carried out at 77K. The tube is subjected to a quasi-static (“DC”) uniform magnetic field. A Hall probe measures the three components of the local magnetic induction along the axis of the tube as a function of the applied magnetic induction. Results show that the shielding performances in the axial configuration are highly improved at the closed extremity as the cap reduces the penetration through the open end. The shielding factor distribution along the tube axis is affected by the presence of the cap. For an open tube, the shielding factor is maximum near the center and decreases towards both extremities. For the tube closed at one extremity, the shielding factor is maximum at the closed extremity and decreases towards the center. Moreover, the shielding factor distribution between the tube center and the open extremity is not affected by the presence of the cap. The experimental results show that, a small gap between the tube and the cap, which can be necessary for applications, does not strongly affect the magnetic shielding performances of the assembly. [less ▲]

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See detailSimulation of the convective cooling of a bulk superconductor by a coupling electromagnetic-fluid model
Kirsch, Sébastien; Fagnard, Jean-François ULiege; Dubois, Charles et al

Poster (2014, August)

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See detailExperimental study of GdBCO pellets subjected to small transverse alternating magnetic fields at very low frequency: Evidence of saturation of the axial magnetization decay
Fagnard, Jean-François ULiege; Kirsch, Sébastien; Teshima, Hidekazu et al

Poster (2014, August)

Due to their ability to trap large magnetic inductions, bulk (RE)BCO materials (where RE stands for rare-earth ion) can be used as powerful permanent magnets. Previous works have shown that the ... [more ▼]

Due to their ability to trap large magnetic inductions, bulk (RE)BCO materials (where RE stands for rare-earth ion) can be used as powerful permanent magnets. Previous works have shown that the magnetization of a bulk superconductor can be destroyed by the presence of an ac magnetic field applied transversally to the remnant magnetization. Up to now, the exact process of this magnetization decay is not completely understood, i.e. it is not clear if the decay is only due to a redistribution of the superconducting currents in the volume of the pellet or if a part of this decay can be due to self-heating of the material subjected to the ac excitation. In this work, we carry out, in liquid nitrogen, measurements for which the ac field is applied during several hours. We investigate the range of relatively small ac field amplitudes (in comparison to the penetration field of the pellet) and in a wide range of low frequencies (1mHz–20Hz). The waveform of the parasitic ac field is either sinusoidal or triangular, the latter corresponding to a constant variation of the applied induction, dBapp/dt. The studied sample is a cylindrical bulk single grain GdBCO pellet whose dimensions are 10mm in height and 15mm in diameter. Thermocouples are placed on the pellet surface to probe possible self-heating of the material during the experiments. A high sensitivity cryogenic Hall probe is placed close to the surface to measure the local magnetic induction normal to the surface (and parallel to the transverse ac field). The results show first that, for a given number of applied triangular transverse cycles, lower values of dBapp/dt induce larger magnetization decays.. An important feature of practical interest is that, after a very large number of cycles (>10000) which cause the removal of a given amount of magnetization (depending on the amplitude and the frequency of the field), the rate of the magnetization decay goes back to its initial value, corresponding to the relaxation of the superconducting currents due to flux creep only. The thermocouples show no evidence of self-heating in that range of amplitude and frequency of the applied field. Acknowledgements We thank the FRS-FNRS, the Communauté Française de Belgique for cryofluid, travel and equipment grants, under reference ARC 11/16-03. [less ▲]

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See detailMagnetic flux distribution and hysteresis properties of bulk high temperature ferromagnet / superconductor / ferromagnet hybrid structures
Philippe, Matthieu ULiege; Ainslie, Mark D; Fagnard, Jean-François ULiege 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 characterisation of large grain, bulk Y–Ba–Cu–O superconductor–soft ferromagnetic alloy hybrid structures
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Kirsch, Sébastien ULiege et al

in Physica C: Superconductivity (2014), 502

Large grain, bulk Y–Ba–Cu–O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In ... [more ▼]

Large grain, bulk Y–Ba–Cu–O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In the present work, we investigate how the trapped field of such magnets can be improved by combining bulk YBCO with a soft FeNi, ferromagnetic alloy. This involves machining the alloy into components of various shapes, such as cylinders and rings, which are attached subsequently to the top surface of a solid, bulk HTS cylinder. The effect of these modifications on the magnetic hysteresis curve and trapped field of the bulk superconductor at 77 K are then studied using pick-up coil and Hall probe measurements. The experimental data are compared to finite element modelling of the magnetic flux distribution using Campbell’s algorithm. Initially we establish the validity of the technique involving pick-up coils wrapped around the bulk superconductor to obtain its magnetic hysteresis curve in a non-destructive way and highlight the difference between the measured signal and the true magnetization of the sample. We then consider the properties of hybrid ferromagnet/superconductor (F/S) structures. Hall probe measurements, together with the results of the model, establish that flux lines curve outwards through the ferromagnet, which acts, effectively, like a magnetic short circuit. Magnetic hysteresis curves show that the effects of the superconductor and the ferromagnet simply add when the ferromagnet is saturated fully by the applied field. The trapped field of the hybrid structure is always larger than that of the superconductor alone below this saturation level, and especially when the applied field is removed. The results of the study show further that the beneficial effects on the trapped field are enhanced when the ferromagnet covers the entire surface of the superconductor for different ferromagnetic components of various shapes and fixed volume. [less ▲]

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See detailCoupled electromagnetic-fluid modelling of a bulk superconductor cooled by a cryogenic fluid
Kirsch, Sébastien; Fagnard, Jean-François ULiege; Dubois, Charles et al

Conference (2014, May 13)

The electric and magnetic performance of a superconductor are strongly dependent of its temperature. For that reason, the cooling of the superconductor material is an important matter, especially for bulk ... [more ▼]

The electric and magnetic performance of a superconductor are strongly dependent of its temperature. For that reason, the cooling of the superconductor material is an important matter, especially for bulk superconductors, which favor low heat transfers because of their low thermal conductivity and the large volume to surface ratio. Usually, heat transfers between a bulk superconductor and the cooling fluid is modelled by a simplified law depending on a convective coefficient and the temperature difference between the fluid and the bulk surface. In practice, however, the heat flux depends also on the geometry of the superconductor and its orientation. Its experimental determination can be difficult and requires considering realistic setups, as effectively used in applications. The goal of this work is to model, in addition to the electromagnetic behaviour of the superconductor, the cooling fluid flow. We focus on the case of a bulk superconductor heated by induced AC losses. The hot surface of the superconductor initiates convective motion in the fluid, which will cool down the superconductor. This coupling effect is modelled using a finite element approach for both the fluid flow and the superconductor. The model is validated experimentally thanks to Particle Image Velocimetry (PIV) methods performs at room temperature with oil. The heat transfers are then estimated and compared with results from the conventional simplified model, in order to understand better its ranges of applicability. [less ▲]

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See detailMagnetic screening with bulk high-temperature superconducting hollow tubes in the “emission” configuration
Vanderbemden, Philippe ULiege; Hogan, Kevin ULiege; Wera, Laurent ULiege et al

Conference (2014, April 28)

Due to their unique ability to trap magnetic fields exceeding the saturation limit of conventional ferromagnetic materials, bulk superconductors can be used successfully in motors and generators. In ... [more ▼]

Due to their unique ability to trap magnetic fields exceeding the saturation limit of conventional ferromagnetic materials, bulk superconductors can be used successfully in motors and generators. In several topologies however, the stray magnetic field produced by the superconducting magnet or coils needs to be strongly reduced outside the device. The screening can be performed using either active or passive magnetic screens. In this respect, a hollow tube made of bulk high temperature superconducting (HTS) material provides a strong attenuation of external low frequency magnetic fields and acts as a very efficient passive screen. The situation where the stray magnetic field generated by an electromagnetic device (e.g. a motor or a generator) needs to be attenuated corresponds to an “emission” problem. In the present work, we report the magnetic behaviour of a bulk HTS hollow cylinder in the “emission” configuration, i.e. a coil is placed inside the cylinder and the magnetic field is recorded outside the cylinder. We study the configuration where the coil is placed in the central part of the superconducting cylinder, either along its axis (axial configuration) or perpendicular to it (transverse configuration). The distribution of magnetic field at several distances of the generating coil is measured by miniature Hall probe mapping. Results show the significant attenuation of the magnetic field provided by the superconductor as well as the dependence with respect to the sweep rate. The experimental data are analyzed by comparing the behaviour of the superconductor in the inhomogeneous and homogeneous magnetic field configurations. It is shown that a simple analytical model is able to reproduce the behaviour of the superconductor in the axial configuration [less ▲]

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See detailStructural, magnetic and magneto-transport properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3
Thaljaoui, R.; Boujelben, W.; Pękała, M. et al

in Journal of Alloys and Compounds (2014), 611(0), 427-432

Pr0.55K0.05Sr0.4MnO3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single ... [more ▼]

Pr0.55K0.05Sr0.4MnO3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with Pnma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000–1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic–ferromagnetic transition at the Curie temperature TC = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg−1 K−1, resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013). [less ▲]

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See detailMagnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0 to 0.2)
Thaljaoui, R.; Boujelben, W.; Pękała, M. et al

in Journal of Magnetism and Magnetic Materials (2014), 352(0), 6-12

Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with ... [more ▼]

Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition. [less ▲]

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See detailMeasurement of the magnetic hysteresis cycle of bulk superconductor / ferromagnet hybrids
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Wera, Laurent ULiege et al

Conference (2013, November 07)

Large grain, bulk YBa2Cu3O7-δ (YBCO) high temperature superconductors (HTS) can be potentially used as powerful permanent magnets for magnetic levitation. The magnetic flux distribution above a bulk HTS ... [more ▼]

Large grain, bulk YBa2Cu3O7-δ (YBCO) high temperature superconductors (HTS) can be potentially used as powerful permanent magnets for magnetic levitation. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform compared to the rather flat distribution above a ferromagnet. In the present work, we study experimentally how cylindrical pieces of FeNi soft ferromagnetic alloys can be combined with a cylindrical, bulk, large grain YBCO superconductor to improve the distribution of the trapped field at the surface or its average value through the volume of the sample. The magnetic properties of each hybrid structure are measured at 77 K under axial magnetic field up to 3 T. The remanent induction distribution near the top and bottom surfaces is determined by miniature Hall probe mapping. Pick-up coils wound around the superconductor are used to measure the average flux density inside the superconductor. This technique relies on low level voltage measurements (typically a few microvolts) and allows non-destructive measurement of the average magnetic hysteresis curve of the entire bulk superconductor. [less ▲]

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See detailSemi-analytical study of AC losses in an infinitely long superconducting cylinder surrounded by a metallic sheath: magnetic field dependent critical current density and generation of harmonics
Kirsch, Sébastien ULiege; Fagnard, Jean-François ULiege; Vanderbemden, Philippe ULiege et al

in Superconductor Science and Technology (2013), 26

We study the AC losses in an infinitely long cylinder made of a superconducting core surrounded by a non-magnetic metallic sheath and subjected to an axial magnetic field. The losses are computed by ... [more ▼]

We study the AC losses in an infinitely long cylinder made of a superconducting core surrounded by a non-magnetic metallic sheath and subjected to an axial magnetic field. The losses are computed by assuming the Bean–Kim model for the superconductor and Ohmic dissipation for the metal. The time varying magnetic flux crossing the superconductor induces eddy currents in the metal sheath and, due to the nonlinear response of the superconducting material, generates harmonics in the metal current density. In turn, these currents generate distorted magnetic fields acting back on the superconductor. This coupling mechanism is sensitive to the magnetic constitutive law of the superconductor and affects both the waveform of the fields and the total losses. In this paper, we study the importance of the harmonics in the metal on the total losses, as well as their sensitivity to a field dependent critical current density following Kim's law. [less ▲]

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See detailCharacterization of structures with a complex disposition of YBCO coated conductors for magnetic shielding applications
Wera, Laurent ULiege; Fagnard, Jean-François ULiege; Levin, G. A. et al

Poster (2013, September 16)

An efficient superconducting magnetic shield can be built as an assembly of YBCO 2G coated conductor sections. Each section is milled and placed around a cylindrical support in order to form a joint free ... [more ▼]

An efficient superconducting magnetic shield can be built as an assembly of YBCO 2G coated conductor sections. Each section is milled and placed around a cylindrical support in order to form a joint free superconducting loop where persistent currents can flow and provide a strong attenuation of a magnetic field. Our previous works have shown that this assembly is able to shield an axial quasi static (“DC”) magnetic field and that the shielding performances depend on the aspect ratio and the number of layers. The purpose of the present work is to study experimentally the shielding efficiency of several structures with a more complex orientation and position of YBCO coated conductors. Our aim is to design a magnetic shield that would be able to shield a magnetic field directed at any angle with respect to the superconducting loops. Such a structure can be obtained by placing pairs of coated conductors sections along three orthogonal axes. All experiments are carried out at 77K. The structure is subjected to a quasi-static (“DC”) magnetic field. A Hall probe measures the three components of the local magnetic induction inside the assembly as a function of the applied magnetic induction. The shielding efficiency of the structure is characterized as a function of (i) the magnetic field amplitude, (ii) the position of the Hall probe along the three axes, and (iii) the angles between the applied magnetic field and each axis. The experimental results allow us to determine the shielding efficiency in the central part of the new 3-axes structure. Although the shielding efficiency is lowered with respect to that of the traditional 1-axis-coil geometry, measurements at different field orientations allow us to identify the role played by each of the pairs of coils in screening the external magnetic field. [less ▲]

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See detailNumerical modelling of the magneto-thermal effects of a transverse AC magnetic field on the axial magnetization of a bulk superconducting cylinder
Kirsch, Sébastien; Fagnard, Jean-François ULiege; Vanderbemden, Philippe ULiege et al

Poster (2013, September)

We study the decrease of the magnetization of a bulk superconducting sample when it is subjected to a perpendicular AC magnetic field (\crossed field" configuration). The effect of a transverse AC ... [more ▼]

We study the decrease of the magnetization of a bulk superconducting sample when it is subjected to a perpendicular AC magnetic field (\crossed field" configuration). The effect of a transverse AC magnetic field on the permanent magnetization of the supercon- ductor are twofold: (i) the superconducting currents are redistributed in the supercon- ductor, and (ii) AC losses are generated, which may locally increase the temperature and degrade the superconducting properties. These two phenomena (current redistribution and losses) are differently affected by the frequency and the amplitude of the transverse magnetic field. The goal of this study is to identify the sets of experimental conditions that accentuate each of these two effects, and more specifically to assess their importance in crossed field experiments being carried in our research group. The cylindrical superconductor is surrounded by a metallic sheath and is initially magnetized along its symmetry axis. The magneto-thermal modelling is carried out by using a finite element method (FEM) implemented in a open source package (GetDP). The validity of these simulations is verified by comparing modelling results with experi- mental data obtained for small amplitudes and large numbers of cycles for the transverse magnetic field. [less ▲]

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See detailDecay of the axial magnetization of GdBCO pellets subjected to small transverse alternating magnetic fields.
Fagnard, Jean-François ULiege; Kirsch, Sébastien; Teshima, Hidekazu et al

Poster (2013, September)

Bulk (RE)BCO materials (where RE denotes a rare-earth ion) are known to be used as strong permanent magnets in various engineering devices, such as magnetic bearings or rotating machines. In so doing, the ... [more ▼]

Bulk (RE)BCO materials (where RE denotes a rare-earth ion) are known to be used as strong permanent magnets in various engineering devices, such as magnetic bearings or rotating machines. In so doing, the bulk pellet is usually magnetized along its c-axis and a permanent magnetic moment is trapped. In real application, however, the pellet is likely to be subjected to small parasitic magnetic fields that cause a decay of the permanent magnetic moment. The most severe effects arise when the pellets are subjected to ac magnetic field cycles that are perpendicular to their c- axis (“crossed-fields” configuration). Our previous works relate to a small number of transverse cycles of large amplitude. In the present work we consider a large number (> 10^4) of cycles of small amplitude, which is closer to practical situations. The study is carried out on bulk single grain GdBCO pellet. The samples are two 10 mm height and 15 mm diameter cylinders, one of which is surrounded by a 2 mm thick stainless steel reinforcement ring. The transverse field is sinusoidal, its frequency ranges between 10 Hz and 800 Hz and its amplitude ranges between 5 mT and 50 mT. The resulting decay of the axial magnetization of the samples is recorded against time and flux-creep effects are subtracted. Thermocouples are placed at several locations on the samples surface to probe possible heating. For these small amplitudes of the magnetic field, corresponding to only few percents of the penetration field, results show that the magnetization decay depends mainly on the time during which the transverse field is applied. This is in contrast with results obtained at larger amplitudes of the magnetic field and for which the decay is linked to the number of cycles. We also show that the natural relaxation of the axial magnetization is strongly affected or even suppressed after a short time exposition to the transverse ac magnetic field. Acknowledgements We thank the FRS-FNRS, the Communauté Française de Belgique for cryofluid, travel and equipment grants, under reference ARC 11/16-03. [less ▲]

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See detailMagnetic hysteresis cycle and remnant field distribution of bulk high temperature superconductor / ferromagnet hybrids
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Wera, Laurent ULiege et al

Poster (2013, September)

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean ... [more ▼]

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean model) compared to the rather flat distribution above a ferromagnet. In the present work, we study how FeNi soft ferromagnetic alloys of different shapes can be combined with a bulk, large grain (RE)BCO superconductor (RE denotes a rare-earth element) to improve the distribution of trapped field at the surface or its average value through the volume of the sample. A FeNi ferromagnetic alloy was machined into pieces of various shapes (cylinders and rings) and attached to (i) the top surface of the bulk HTS cylinder to form bulk ferromagnet / superconductor (F/S) hybrids and (ii) to the top and bottom surfaces to form bulk F/S/F hybrids. The magnetic properties of each hybrid structure were measured under axial magnetic field at 77 K. Pick-up coils wound around the superconductor were used to measure the average magnetic induction inside the superconductor while the remnant induction distribution near the top and bottom surfaces was determined by miniature Hall probe mapping. The modifications of the hysteresis curves and flux distributions were analyzed by taking into account the ferromagnet intrinsic properties (intrinsic permeability, saturation) and geometrical properties (shape, size and volume). The results show that the effect of the ferromagnet increases with its volume. In presence of a ferromagnet, the superconductor hysteresis curve shows a combination of a diamagnetic and a ferromagnetic behaviour on which it is worth noting that (i) the bulk remnant magnetization increases and (ii) in the magnetic saturation regime of the ferromagnet, the magnetic effects of the superconductor and the ferromagnet are superimposed. The results also give evidence that flux lines curve through the ferromagnetic component, which produces a decrease of the self-demagnetizing field inside the superconductor. [less ▲]

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See detailYBCO superconducting thick films: electrophoretic deposition (EPD) on non-planar silver substrates
Namburi, Devendra Kumar ULiege; Closset, Raphaël ULiege; Fagnard, Jean-François ULiege et al

Conference (2013, January 30)

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop ... [more ▼]

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop the superficial charge on the YBCO particles in order to promote migration during the process of electrophoresis. YBCO thick films were deposited on silver tubes and half-tubes by electrophoretic deposition (EPD). The EPD parameters (deposition voltage, deposition time, number of layers etc.) were optimized with respect to the microstructural properties of the YBCO layers after an intermediate heat treatment at 920°C. An essential criterion is the minimization of macrocracks after the 920°C heat treatment, since it was found to favour good superconducting properties after the final heat treatment. This final heat treatment involves (i) partial melting above the peritectic temperature, (ii) peritectic recombination at lower temperature and (iii) reoxygenation at 500°C. Finally, the superconducting properties of the best films are discussed. A uniformly coated 55μm-thick YBCO film on a curved Ag substrate showed excellent superconducting properties with the onset of critical temperature at 92.2 K and an associated sharp resistive transition with transition width < 1 K. [less ▲]

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See detailMagnetic susceptibility and electron magnetic resonance study of monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3
Thaljaoui, R.; Pękała, K.; Pękała, M. et al

in Journal of Alloys and Compounds (2013), 580(0), 137-142

The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the ... [more ▼]

The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature. [less ▲]

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See detailAC Magnetic Measurements on Superconductors: Design of a Device for Magneto-Thermal Measurements
Laurent, Philippe ULiege; Fagnard, Jean-François ULiege; Vanderbemden, Philippe ULiege

in Lay Ekuakille, Aymé (Ed.) Advanced Instrument Engineering: Measurement, Calibration, and Design (2013)

This work describes the design and realisation of an apparatus to measure simultaneously the AC magnetic properties and the temperature distribution on the top surface of bulk superconducting samples (up ... [more ▼]

This work describes the design and realisation of an apparatus to measure simultaneously the AC magnetic properties and the temperature distribution on the top surface of bulk superconducting samples (up to 32 mm in diameter) in cryogenic conditions (temperature range 78-120 K). First we describe the experimental set-up used for simultaneous thermal and magnetic characterization of the sample. Next we describe the practical considerations required for generating the large AC magnetic fields, possibly in the presence of DC fields. In the third section we present a custom-made high speed data acquisition system for replacing the laboratory devices (DC voltmeter and AC lock-in amplifiers) when both temperature and magnetic data need to be recorded at high a sampling rate. The performances and limitations of the system are discussed. [less ▲]

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See detailMagnetic properties and anisotropy of orthorhombic DyMnO3 single crystal
Pękała, M.; Wolff-Fabris, F.; Fagnard, Jean-François ULiege et al

in Journal of Magnetism and Magnetic Materials (2013), 335(0), 46-52

An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The ... [more ▼]

An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of a cubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6 T. [less ▲]

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See detailThe influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y-Ba-Cu-O
Marchal, C.; Fagnard, Jean-François ULiege; Shi, Y. H. et al

in Superconductor Science and Technology (2013), 26

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor ... [more ▼]

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material. © 2013 IOP Publishing Ltd. [less ▲]

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