A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors

Egan, Raphael; Philippe, Matthieu; Wera, Laurent; Fagnard, Jean-François; Vanderheyden, Benoît; Dennis, Anthony; Shi, Yunhua; Cardwell, D. A.; Vanderbemden, Philippe

doi:10.1063/1.4907903

Cited by 6 publications

(9 citation statements)

References 36 publications

(50 reference statements)

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“…This procedure gives a magnetic moment at zero applied field equal to 0.092 Am 2 . This value is in very close agreement with the magnetic moment of the same sample determined using the flux extraction magnetometer developed by Egan et al 17 , i.e. m = (0.089 ± 0.01) Am 2 .…”

Section: Resultssupporting

confidence: 90%

“…A first observation is the fact that the magnetic moment is systematically higher at T = 77 K than at room temperature. These data can be compared to the magnetic moment of the same magnet, measured at zero applied field using a flux extraction magnetometer developed for large samples up to 17 mm in diameter 17 : m = (1.40 ± 0.01) Am 2 at 300 K and m = (1.47 ± 0.01) Am 2 at 77 K. The magnetic moments obtained with the flux extraction magnetometer are therefore fully consistent with the results displayed in Fig. 4, and confirm the ∼ 5% increase of the magnetic moment between 300 K and 77 K. This slight increase is in agreement with recent observations and elements of explanation about the evolution of the remnant field at low temperature in Nd 2 Fe 14 B permanent magnets that were studied by Dies-Jimenez et al 56 .…”

Section: Resultsmentioning

confidence: 99%

“…Several efforts were made to develop AC susceptometers 14,15 or DC magnetometers 16 suited to large-size magnetic materials. These include a recent magnetometer based on a flux extraction device to measure the magnetic moment of large samples (a few cm 3 ) in a non-destructive way 17 . In order to ensure that the electromagnetic force across the sensing coils is sensitive to the magnetic moment, however, these sensing coils should be dimensioned carefully and, in general, should be much larger than (at least twice) the sample size 17,18 , which becomes problematic for large geometric dimensions.…”

Section: Introductionmentioning

confidence: 99%

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A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Brialmont

Fagnard

Vanderbemden

2019

Review of Scientific Instruments

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The development of large size magnetic materials requires non-destructive measurement techniques to characterize their magnetic moment. In this work we report the design and construction of a torque magnetometer able to accommodate sizable magnetic samples (> 1 cm 3) both at room and cryogenic temperature. This device has an intermediate sensitivity between miniature torque magnetometers designed to work at cryogenic temperature and industrial torquemeters poorly adapted to extreme conditions. We show that torque sensing in the range 10 −3-100 Nm can be achieved with piezoresistive metallic strain gages cemented on a cylindrical aluminum shaft with external temperature control. An absolute calibration of the device, carried out with a coil fed by a DC current, shows that magnetic moments down to 5 × 10 −3 Am 2 can be measured by this technique. The magnetometer is used to characterize a Nd-Fe-B permanent magnet and a permanently magnetized bulk, large grain superconductor at liquid nitrogen temperature (77 K). Results are in excellent agreement with data obtained with a flux extraction magnetometer for large samples. The device is able to measure magnetic moments in excess of 1.5 Am 2 , i.e. two orders of magnitude above the maximum magnetic moment of commercial magnetometers. The sample can be inserted in the air-gap of an electromagnet to measure the decrease of magnetic moment in the presence of a transverse applied field. The device was used to characterize the magnetic moment of 'quasi-bulk' superconductors made of stacked coated conductor tapes (12 mm width) in such 'crossed field' conditions.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Brialmont

Fagnard

Vanderbemden

2019

Review of Scientific Instruments

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“…The magnetic characterization of this sample at 77 K was presented in our previous work [29,34]. The field dependent critical current J c (B) is experimentally found to follow a Bean-Kim law c ( ) = …”

Section: Superconducting Samplementioning

confidence: 99%

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

Philippe

Ainslie

Wera

et al. 2015

Supercond. Sci. Technol.

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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 thicknessdependence 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. [5,6]) is well beyond the saturation magnetization of conventional ferromagnets. This makes them extremely promising as a competing technology for traditional permanent magnets in various applications [7][8][9][10]. The combination of ferromagnetic and superconducting materials can enhance the performance of the superconductor [11,12] and even lead to new applications [13]. Large grain, bulk superconductors are often used in applications that incorporate ferromagnetic materials, such as in motors and generators [14,15]. Ferromagnets can also increase the force in levitation systems [16,17] and close the magnetic circuit, which improves the available flux produced by bulk superconductors [18]. Similarly, ferromagnetic materials are used as sheaths around multifilament wires and tapes [19,20] or as magnetic flux diverters to modify the flux distribution around tapes and superconducting coil magnets [21][22][23][24][25][26][27][28]; thereby improving their electrical properties (i.e. increasing the critical current and reducing AC losses).

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“…The specifications and the operations of the experimental system are described in a previous work [41]. The magnetometer is able to measure very large magnetic moments (up to 1 Am²), which is two orders of magnitude above the maximum magnetic moment of commercial cryogenic measurement systems.…”

Section: Methodsmentioning

confidence: 99%

Magnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling

Fagnard¹,

Morita²,

Nariki³

et al. 2016

Supercond. Sci. Technol.

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Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been pointed out that ferromagnets can help in reducing the crossed field effect, namely the magnetization decay that is observed under the application of AC transverse magnetic fields. In this work, we pursue a detailed study of the influence of the geometry of the ferromagnetic part on both trapped fields and crossed field effects. The magnetic properties of the hybrid superconducting / soft ferromagnetic structures are characterized by measuring the magnetic moment with a bespoke magnetometer and the local magnetic field density with Hall probes. The results are interpreted by means of 2D and 3D numerical models yielding the distribution of the superconducting currents as a function of the ferromagnet geometry. We examine in details the distortion of the shielding superconducting currents distribution in hybrid structures subjected to crossed magnetic fields. These results confirm the existence of an optimum thickness of the ferromagnet, which depends on the saturation magnetization of the ferromagnetic material and the current density of the superconductor. A hybrid structure providing an efficient protection against the crossed magnetic field while maintaining the magnetic induction along the axis of the structure is suggested. The limitations of the 2D modelling in this configuration are discussed.

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A flux extraction device to measure the magnetic moment of large samples; application to bulk superconductors

Cited by 6 publications

References 36 publications

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

Magnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling

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