A high-saturation Fe-27Co material with microalloying additions

In applications requiring a large magnetic force, permanent magnets with non-parallel magnetization directions can be assembled in a Halbach array to generate a large gradient of magnetic flux density. The saturation magnetization of permanent magnets, however, brings a fundamental limit on the performance of this configuration. In the present work, we investigate experimentally the assembly of cuboid bulk, large grain melt-textured YBa2Cu3O7−x superconductors (∼14×14×14 mm3) with orthogonal c-axes so as to form a basic unit of Halbach array. The experiments are carried out at 77 K. The experimental distribution of the magnetic flux density above the array of trapped-field superconductors is compared to a similar array made of permanent magnets. A simple analytical model is developed and is shown to accurately reproduce the main experimental observations. The results suggest that a redistribution occurs in the current flowing in the central sample when the distance between the superconductors is reduced, whereas the neighbouring superconductors are unaffected. It is shown that this current redistribution yields a reduced contribution of the central sample to the magnetic flux density above the centre of the array and a new negative contribution associated with stray fields to the magnetic flux density at this location. This interpretation is confirmed by modelling of the distribution of transport currents in the superconductor using a 3D finite element model.

Section: Analytical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Trapped magnetic field distribution above a superconducting linear Halbach array

Houbart

Fagnard

Dular

et al. 2022

“…Unlike conventional permanent magnets, which are limited by their saturation magnetization, e.g. 1.4 tesla for Nd-Fe-B [6], superconductors do not exhibit the same limitation. Their trapped field ability can be enhanced by increasing their dimensions [7].…”

Section: Introductionmentioning

confidence: 98%

Trapped magnetic field distribution above two magnetized bulk superconductors close to each other

Houbart¹,

Fagnard²,

Dennis³

et al. 2020

Bulk large-grain superconductors can be used as high-field permanent magnets. Although the properties of such individual trapped field magnets are well documented, much less is known concerning their behaviour when two are brought together. In this work, the interaction between two cylindrical bulk YBa 2 Cu 3 O 7 (YBCO) superconductors is described. Two sets of experiments were carried out. The first involved the simultaneous magnetization of two bulk superconductors placed a short distance apart. Here, the applied magnetic field was aligned parallel to the c-axis of one bulk, while the other was oriented with its c-axis offset . For a centre-to-centre distance equal to twice the sample height, the presence of the second sample is found not to alter the current distribution inside the first. Consequently, the contribution of both samples simply sums, thus increasing the magnetic flux density between them. In the second set of experiments, the translational approach of the superconductors with parallel c-axes was investigated. The following configurations were considered: (i) face to face approach (with anti-parallel trapped field orientation) and (ii) sideways approach (with parallel trapped field orientation). An irreversible decrease of the trapped field was measured on separation . Repeated approach cycles showed that the irreversible loss of trapped field is largest for the first approach.

“…The uniform DC field is exploited to ensure full saturation magnetization of the magnetic material on which the force is acting while the soft ferromagnetic core introduces a localized distortion of the homogeneous field, thereby generating the required gradient. In this approach, however, the saturation magnetization of the soft ferromagnetic core employed limits the maximum achievable field gradient (µ 0 M sat ∼ 2.4 T for soft ferromagnetic Fe-Co alloys [9]).…”

Section: Introductionmentioning

confidence: 99%

Enhancing the magnetic field gradient between two superconductors with rotational motion under a background DC field

Houbart,

Fagnard,

Harmeling

et al. 2024

The ability of bulk high-temperature superconductors to trap magnetic flux densities up to one order of magnitude larger than the saturation magnetization of conventional ferromagnetic materials offers the prospect of generating large magnetic flux density gradients. Combining multiple superconductors, akin to assembling a Halbach array of permanent magnets, may increase the generated gradient even further. The associated challenge is that superconductors are prone to demagnetization when exposed to field components perpendicular to their main magnetization direction. In the present work, we investigate the magnetic flux density gradient achieved with a pair of cubic, bulk, large-grain melt-textured superconductors in the presence of a background DC magnetic field at 77 K. We investigate the increase of the performance when decreasing the temperature down to 59 K. The studied configuration consists in two facing cubic YBa2Cu3O7-x superconductors of 6 mm side with anti-parallel magnetization directions. It is obtained after the simultaneous magnetization of the samples followed by a rotation of 180° of the top superconductor. Although the background field reduces the trapped field ability of individual samples, it is shown that this phenomenon is significantly mitigated at 65 K and at 59 K compared to 77 K. The results reveal that a sample-to-sample distance (∼ 16 mm) of the order of their size is sufficient to avoid any mutual demagnetization effect during the rotational motion. Furthermore, it is shown that decreasing the temperature is not only beneficial in increasing the field and field gradient achieved but also in extending the range of background fields in which the superconductor can be rotated without demagnetization. This superconducting assembly yields a magnetic flux density gradient exceeding that of an isolated superconductor and has the potential to surpass the capabilities of permanent magnets.