Publications et communications de Matthieu Philippe [a032256]
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See detailInfluence of crossed fields in structures combining large grain, bulk (RE)BCO superconductors and soft ferromagnetic discs
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Wera, Laurent ULiege et al

in Journal of Physics: Conference Series (2016), 695

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When ... [more ▼]

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When such superconducting (SC) “trapped field magnets” are combined to a ferromagnetic (FM) disc, the total magnetic moment is increased with respect to that of the superconductor alone. In the present work, we study experimentally the magnetic behaviour of such hybrid FM/SC structures when they are subjected to cycles of applied field that are orthogonal to their permanent magnetization, i.e. a “crossed-field” configuration. Experimental results show that the usual “crossed-field demagnetization” caused by the cycles of transverse field is strongly reduced in the presence of the ferromagnet. [less ▲]

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See detailThermal properties of Ti-doped Cu–Zn soft ferrites used as thermally actuated material for magnetizing superconductors
Stachowiak, Piotr; Mucha, Jan; Szewczyk, Daria et al

in Journal of Physics : D Applied Physics (2016), 49

A great majority of widely used ferrite ceramics exhibit a relatively high temperature of order–disorder phase transition in their magnetic subsystem. For applications related to the magnetization process ... [more ▼]

A great majority of widely used ferrite ceramics exhibit a relatively high temperature of order–disorder phase transition in their magnetic subsystem. For applications related to the magnetization process of superconductors, however, a low value of Tc is required. Here we report and analyze in detail the thermal properties of bulk Ti-doped Cu–Zn ferrite ceramics Cu0.3Zn0.7Ti0.04Fe1.96O4 and Mg0.15Cu0.15Zn0.7Ti0.04Fe1.96O4. They are characterized by a Curie temperature in the range 120–170 K and a maximum DC magnetic susceptibility exceeding 20 for the Cu0.3Zn0.7Ti0.04Fe1.96O4 material. The temperature dependence of both the specific heat Cp and of the thermal conductivity κ, determined between 2 and 300 K, are found not to exhibit any peculiar feature at the magnetic transition temperature. The low-temperature dependence of both κ and the mean free path of phonons suggests a mesoscopic fractal structure of the grains. From the measured data, the characteristics of thermally actuated waves are estimated. The low magnetic phase transition temperature and suitable thermal parameters make the investigated ferrite ceramics applicable as magnetic wave producers in devices designed for magnetization of high-temperature superconductors. [less ▲]

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See detailInfluence of soft ferromagnetic materials on the magnetic flux density above large grain, bulk high temperature (RE)BCO superconductors: measurements and modelling
Philippe, Matthieu ULiege; Ainslie, Mark D; Fagnard, Jean-François ULiege et al

Poster (2015, September)

Due to their ability to trap high magnetic fields, bulk (RE)BCO superconductors can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic ... [more ▼]

Due to their ability to trap high magnetic fields, bulk (RE)BCO superconductors can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. We combine soft ferromagnetic pieces with bulk, large grain (RE)BCO high temperature superconductors to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how the ferromagnetic pieces influence (i) the profile shape of the trapped magnetic flux density at the surface of each structure and (ii) the decrease of the trapped field under an applied field that is orthogonal to the main magnetization (crossed field configuration). Hall probe mappings of the trapped magnetic flux density profile above the hybrid structures at 77 K are compared to modelled profiles using a 2D finite element method. Modelling results are in excellent qualitative and quantitative agreement with the measurements. The model is then used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and ferromagnet geometries. For the modelled configurations, the magnetic flux density is enhanced on the face opposite to the ferromagnet. Both thickness and saturation magnetization of the ferromagnetic material are found to be important parameters. The saturation regime of the ferromagnet can be predicted using a simple analytical model. We show that thin ferromagnetic discs can be driven to full saturation even though the superconductor magnetic field is much smaller than their saturation magnetization. Remarkably, the beneficial influence of the ferromagnet on the trapped field can be observed even if the trapped flux density above the superconductor is much larger than the ferromagnet saturation magnetization. Finally, we show that the ferromagnetic material acts as a magnetic shield and lowers the relative demagnetization effect caused by the application of transverse (crossed) magnetic field cycles. [less ▲]

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See detailTrapped magnetic flux density and influence of crossed fields in structures combining large grain, bulk (RE)BCO superconductors and soft ferromagnetic discs
Philippe, Matthieu ULiege; Ainslie, Mark D; Fagnard, Jean-François ULiege et al

Conference (2015, September)

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. We ... [more ▼]

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. We combine soft ferromagnetic pieces with bulk, large grain (RE)BCO high temperature superconductors to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how a ferromagnetic disc influences the trapped flux density at the surface of a SC/FM structure at 77 K and the magnetic moment of the whole structure. The flux density generated by the superconductor is shielded above the ferromagnet. The saturation of the ferromagnet by the flux of the superconductor is investigated with the help of a finite element model and a simple analytical formula is suggested to determine the saturation threshold. Finally, we show that the ferromagnetic disc lowers the relative demagnetization effect caused by the application of magnetic field cycles orthogonal to the main magnetization (crossed field configuration). [less ▲]

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See detailInfluence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y-Ba-Cu-O superconductor
Philippe, Matthieu ULiege; Ainslie, Mark D; Wera, Laurent ULiege et al

in Superconductor Science and Technology (2015), 28

Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this ... [more ▼]

Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y-Ba-Cu-O (YBCO) high temperature superconductor to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*, saturation of the ferromagnet occurs, and above d*, a weak thickness-dependence is observed. The influence of the ferromagnet is observed even if its saturation magnetization is lower than the trapped flux density of the superconductor. Conversely, thin ferromagnetic discs can be driven to full saturation even though the outer magnetic field is much smaller than their saturation magnetization. [less ▲]

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See detailA flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors
Egan, Raphael ULiege; Philippe, Matthieu ULiege; Wera, Laurent ULiege et al

in Review of Scientific Instruments (2015), 86(2), 025107

We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm3) at cryogenic temperature. The signal is constructed by integrating ... [more ▼]

We report the design and construction of a flux extraction device to measure the DC magnetic moment of large samples (i.e., several cm3) at cryogenic temperature. The signal is constructed by integrating the electromotive force generated by two coils wound in series-opposition that move around the sample. We show that an octupole expansion of the magnetic vector potential can be used conveniently to treat near-field effects for this geometrical configuration. The resulting expansion is tested for the case of a large, permanently magnetized, type-II superconducting sample. The dimensions of the sensing coils are determined in such a way that the measurement is influenced by the dipole magnetic moment of the sample and not by moments of higher order, within user-determined upper bounds. The device, which is able to measure magnetic moments in excess of 1 Am2 (1000 emu), is validated by (i) a direct calibration experiment using a small coil driven by a known current and (ii) by comparison with the results of numerical calculations obtained previously using a flux measurement technique. The sensitivity of the device is demonstrated by the measurement of flux-creep relaxation of the magnetization in a large bulk superconductor sample at liquid nitrogen temperature (77 K). [less ▲]

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See detailCorrelation between morphology and electrical conductivity of dried and carbonized multi-walled carbon nanotube/resorcinol–formaldehyde xerogel composites
Haghgoo, M.; Yousefi, A. A.; Mehr, M. J. Z. et al

in Journal of Materials Science (2015), 20

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See detailMagnetic properties of structures combining bulk high temperature superconductors and soft ferromagnetic alloys
Philippe, Matthieu ULiege

Doctoral thesis (2015)

The purpose of the present work is to determine experimentally and numerically how the magnetic flux density both inside and outside a large grain, bulk high temperature superconductor is modified when ... [more ▼]

The purpose of the present work is to determine experimentally and numerically how the magnetic flux density both inside and outside a large grain, bulk high temperature superconductor is modified when placed in the vicinity of axisymmetric ferromagnetic components. The investigated superconductors are bulk (RE)Ba2Cu3O7 cylinders of a few cm³. The ferromagnets are of various sizes and shapes, machined out of well characterized, soft magnetic alloys of high permeability. Both superconductor and ferromagnet have the same diameter and are cooled at the liquid nitrogen temperature (T = 77 K). The properties of the superconductor / ferromagnet (SC/FM) hybrid structures are investigated through surface (Hall probe) and volume measurements carried out in the fully magnetized remanent state and under complete cycles of field applied either parallel or perpendicular to the sample c axis. The design of a suitable volume characterization method for large samples and its validation through comparison with other measurements is part of the present work. Numerical models based on the Brandt and finite element methods are compared with the measurements and used to investigate configurations and physical quantities that are not accessible experimentally. We show that the ferromagnet acts as a magnetic short-circuit and creates a low reluctance path that drives the flux lines directly towards the edges of the superconducting magnet. The zone above the ferromagnet is shielded from the flux trapped inside the superconductor. Conversely, the flux density can often be enhanced on the face opposite to the ferromagnet (superconductor side); it is suggested that the flux density increase due to the ferromagnet is more significant when combined to a rather thin superconducting pellet. In all the studied cases, the presence of the ferromagnet was found to increase both the average trapped flux inside the superconductor and the magnetic moment of the whole SC/FM structure (including the ferromagnet). The ferromagnet ability to divert magnetic flux lines depends on whether it is partially or fully saturated. This saturation is found to be governed in the remanent state by the ferromagnet thickness d, its saturation magnetization M_sat and the flux produced by the superconductor (proportional to its critical current density J_c). The amount of diverted / shielded flux does not change once the ferromagnet is fully saturated and the effect of the ferromagnet becomes relatively less important as the generated flux increases. Hybrid structures are therefore relevant even when the trapped flux density exceeds the typical saturation magnetization of ferromagnetic materials (≈ 2 T). For a given critical current the higher the saturation magnetization and/or the thicker the ferromagnetic material, the larger the shielding effects on the ferromagnet side and the higher the trapped field on the superconductor face for the investigated sample. For a ferromagnetic disc with the same diameter a as the superconductor, the most suitable ferromagnet thickness d^* can be roughly estimated by a simplified analytical expression d^*≈(J_c0 a^2 )⁄( 6M_sat ), below which nearly full saturation of the FM occurs and above which weak thickness dependence is observed. The magnitude of the supercurrent is an important parameter but its particular J_c (B) dependence is found not to be a crucial parameter affecting the remanent state properties of the modelled hybrid configurations. In addition, the time relaxation of the trapped magnetization was found not to be influenced by the presence of the ferromagnet, within measurement uncertainties. The ferromagnet also influences the magnetic flux density when the assembly is subjected to an external magnetic field. The penetration of the magnetic flux inside the superconductor is delayed in the vicinity of the ferromagnet. The hysteresis loops of the flux density averaged on the superconductor volume show a combination of diamagnetic and ferromagnetic behaviour for SC/FM structures. It appears to be the simple superimposition of the hysteresis cycles of the superconductor and the ferromagnet at high applied field (i.e. exceeding the apparent saturation of the ferromagnet). This simple “addition” rule can be used to effectively predict the magnetic behaviour of larger or more complex hybrid structures and to modulate the magnetic flux density. As in the remanent sate, a thicker ferromagnet has a more significant effect on the whole hysteresis loop of the superconductor, but this effect varies less than proportionally to the increase in the ferromagnet volume. For a given volume of ferromagnetic material, the shape of an unsaturated ferromagnet is not of prime importance provided that the ferromagnet covers the entire surface of the superconductor. A succession of holes and ferromagnetic sections could be used to modulate the flux density. A similar volume of ferromagnetic material was shown to have more influence on the average remanent volume flux density if it is split on both faces of the superconductor to form a FM/SC/FM structure instead of a SC/FM structure. Two additional advantages of ferromagnets were identified in this work. First, the ferromagnet was shown to be beneficial in improving the field gradient – and therefore the magnetic levitation force – outside the superconductor. Second, the addition of the ferromagnetic disc on one side of the superconductor reduces the collapse of the trapped flux density when subjected to several cycles of magnetic field applied perpendicularly to its remanent magnetization (parallel to the c-axis), i.e. in the so-called “crossed-field configuration”. [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 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 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 detailNon-destructive measurement of volume magnetic properties of large, bulk superconductors
Vanderbemden, Philippe ULiege; Dennis, T.; Shi, Y. H. et al

Conference (2012, December 07)

The development of large, single grain bulk superconductors by melt processing techniques has generated a need to characterize samples magnetically over large dimensions, exceeding typically 20 mm in ... [more ▼]

The development of large, single grain bulk superconductors by melt processing techniques has generated a need to characterize samples magnetically over large dimensions, exceeding typically 20 mm in diameter. The usual magnetic characterization gives relies on miniature Hall probe mapping and gives information about the field distribution above the sample surface. If volume properties are required (e.g. magnetization hysteresis loops), the sample needs to be cut in smaller pieces, since the DC magnetic characterization systems for measurements at cryogenic temperatures generally accommodate samples of relatively small size (typically < 5-10 mm diameter). In this work we describe how the hysteresis B(H) loops of large bulk superconducting samples exceeding 10 mm diameter can be determined using home-made sensing coils, either in liquid nitrogen or within the experimental chamber of a Quantum Design Physical Property Measurement System (PPMS). Magnetic properties are measured and compared to those given by several Hall probes attached to both faces of sample. The system is used successfully to measure the DC hysteresis loops of entire (RE)BCO bulk superconducting domains. A careful data acquisition and numerical integration of pick-up coil voltage enables the sweep rate of the magnetic field to be varied from 0.5 to 10 mT/s while keeping an excellent signal/noise ratio. A simple model based on demagnetizing field approach is used to emphasize how the hysteresis loops determined by this technique differ from “true” magnetization loops derived from classical magnetic moment measurements (e.g. SQUID or VSM). These differences are supported with numerical modelling of the average magnetization of the bulk sample using the Brandt method. [less ▲]

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See detailMagnetic behaviour of soft ferromagnetic alloys attached to bulk (RE)BCO superconductors
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Dennis, Anthony et al

Poster (2012, October)

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

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic field distribution around a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean model) compared to the rather flatter distribution around a ferromagnet. In the present work, we study how FeNi soft ferromagnetic alloys of different shapes can be combined with (RE)BCO bulk superconductors to improve the distribution of trapped field or its average value at the surface of the bulk sample. The FeNi ferromagnetic alloys are machined into pieces of various shapes (e.g. cylinder, cone) attached to the bottom surface of the bulk HTS disks. The magnetic properties of each ferromagnetic/superconductor (F/S) assembly are measured under axial magnetic field at 77 K. Small coils and Hall probe mappings provide the average magnetization and field distribution respectively. The results are compared to the intrinsic magnetic hysteresis curves of the magnetic alloys and of the superconductor. Measurements of the average magnetization show that the effects of the ferromagnetic alloys depend mainly on the volume of the ferromagnet and add up to the effect of the superconductor. However, at constant ferromagnetic volume, the shape of the ferromagnetic piece is found to influence the magnetic field penetration and distribution against the top surface of the superconductor. [less ▲]

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