Enhanced trapped field in MgB<sub>2</sub>bulk magnets by tuning grain boundary pinning through milling

Sugino, Sho; Yamamoto, Akiyasu; Shimoyama, Jun–ichi; Kishio, K.

doi:10.1088/0953-2048/28/5/055016

Cited by 30 publications

(19 citation statements)

References 47 publications

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“…On the other hand, the J c decrease for finer grains originated from the fact that the impurities diffusing at the grain surfaces degraded the connectivity between the grains. The similar J c and B T characteristics optimized for the grain size were also found in several reports [11,27,28]. In contrast, the monotonic increase of J c with decreasing grain size was observed for MgB 2 being free from the mechanical milling process [26,29].…”

Section: Introductionsupporting

confidence: 85%

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Naito

Endo

Fujishiro

2017

Supercond. Sci. Technol.

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Grain boundaries are well known to be the predominant pinning centers in MgB 2 superconductors. To study the effects of grain boundaries on the trapped field properties of MgB 2 bulk, we prepared MgB 2 bulks by a spark plasma sintering method using a ball-milled starting powder. The trapped field was maximized for the bulk made from the ball-milled powder with crystallite size, τ, of 27 nm; the highest trapped field, B T , of 2.3 T achieved at 19.3 K was 1.2 times larger than that of the bulk made from the non ball-milled powder (τ = 50 nm). The degradation of the trapped field for the bulk from finer powder (τ = 6 nm) originated mainly from the lowered T c. The critical current density, J c , and the pinning force density, F p , were also maximized for the bulk from τ = 27 nm. The competition between the increase of the numerical density of grain boundaries and the degradation of superconductivity determined the vortex pinning properties for the MgB 2 bulks with mechanically refined grains. The scaling analysis for the pinning force density suggested that the change in the dimension of the dominant pinning source from 2D (surface) to 0D (point) was induced by grain refining. Although the nanometric impurity particles such as MgB 4 , MgO and Mg-B-O were created in the bulk during both ballmilling and spark plasma sintering processes, we considered the point-contact between the refined grains was the predominant point pinning source.

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Section: Introductionsupporting

confidence: 85%

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Naito

Endo

Fujishiro

2017

Supercond. Sci. Technol.

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“…Being simple binary compounds without weak-link natures 58 , large-sized polycrystalline MgB 2 bulks can be produced on an industrial scale. Efforts have been made to increase their trapped magnetic field strength by improving their processing [59][60][61][62] .…”

Section: Introduction To Superconducting Bulk Magnetsmentioning

confidence: 99%

Recent advances in iron-based superconductors toward applications

et al. 2018

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Iron with a large magnetic moment was widely believed to be harmful to the emergence of superconductivity because of the competition between the static ordering of electron spins and the dynamic formation of electron pairs (Cooper pairs). Thus, the discovery of a high critical temperature (Tc) iron-based superconductor (IBSC) in 2008 was accepted with surprise in the condensed matter community and rekindled extensive study globally. IBSCs have since grown to become a new class of high-Tc superconductors next to the high-Tc cuprates discovered in 1986. The rapid research progress in the science and technology of IBSCs over the past decade has resulted in the accumulation of a vast amount of knowledge on IBSC materials, mechanisms, properties, and applications with the publication of more than several tens of thousands of papers. This article reviews recent progress in the technical applications (bulk magnets, thin films, and wires) of IBSCs in addition to their fundamental material characteristics. Highlights of their applications include high-field bulk magnets workable at 15-25 K, thin films with high critical current density (Jc) > 1 MA/cm2 at ~10 T and 4 K, and an average Jc of 1.3*104 A/cm2 at 10 T and 4 K achieved for a 100-m-class-length wire. These achievements are based on the intrinsically advantageous properties of IBSCs such as the higher crystallographic symmetry of the superconducting phase, higher critical magnetic field, and larger critical grain boundary angle to maintain high Jc. These properties also make IBSCs promising for applications using high magnetic fields.Comment: Published online in Materials Today. Open Acces

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“…Although MgB2 cannot compete with the exceptional high field properties of the cuprate HTS compounds, the maximum trapped field achieved in MgB2 bulks of 5.4 T at 12 K [3] is significantly higher than the maximum magnetic fields of about 1.5 T that can be achieved with ferromagnet assemblies [4]. Since the trapped field in bulk superconductors is directly related to critical current density (Jc), extensive research has been carried out to improve Jc(B) performance of MgB2 samples [3,5,6]. Collings et al have pointed out that we need to consider both 'intrinsic' and 'extrinsic' effects when attempting to improve the Jc values in MgB2 [7].…”

Section: Introductionmentioning

confidence: 99%

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB₂ superconductors

gao

Santra

Grovenor

et al. 2022

Supercond. Sci. Technol.

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MgB2 is a promising material for intermediate temperature applications where conventional low temperature superconductors cannot be used, especially if the range of magnetic fields over which is has acceptable current carrying performance can be expanded. However, its applicability is limited by poor properties at elevated magnetic fields. Carbon-based dopants can be used to dramatically improve the high-field performance of MgB2, but at the cost of a reduction in the superconducting transition temperature (Tc) that limits the operation temperature to 20 K or below. Here we report an enhancement of superconducting performance of MgB2 with the addition of cubic and hexagonal boron nitride, without any significant reduction in Tc. Ex-situ bulk samples of MgB2 with two forms of boron nitride addition were manufactured by the field assisted sintering technique (FAST) after high energy ball milling of powder mixtures. We find that hexagonal BN (hBN) nanoparticles mixed homogenously with MgB2 powder react much more easily to produce Mg-N-B impurities than larger cubic BN (cBN) particles (~ 10 µm) under the same processing conditions. The addition of 1 wt% hBN or 5 wt% cBN combined with 6 h of milling has been demonstrated to improve the critical current density (Jc) of MgB2 over the entire magnetic field range. It is proposed that the nano-sized Mg-N-B impurities, that typically reside at MgB2 grain boundaries, increase pinning strength by introducing additional flux pinning centres. In addition, excess Mg may benefit the low-field performance by improving the connectivity. This work shows the significance of microstructural characterization on inhomogeneous superconducting materials to analyse their performance.

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Enhanced trapped field in MgB₂bulk magnets by tuning grain boundary pinning through milling

Cited by 30 publications

References 47 publications

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Recent advances in iron-based superconductors toward applications

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB₂ superconductors

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Enhanced trapped field in MgB2bulk magnets by tuning grain boundary pinning through milling

Cited by 30 publications

References 47 publications

Optimization of vortex pinning at grain boundaries onex-situMgB2bulks synthesized by spark plasma sintering

Optimization of vortex pinning at grain boundaries onex-situMgB2bulks synthesized by spark plasma sintering

Recent advances in iron-based superconductors toward applications

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB2 superconductors

Contact Info

Product

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Enhanced trapped field in MgB₂bulk magnets by tuning grain boundary pinning through milling

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Optimization of vortex pinning at grain boundaries onex-situMgB₂bulks synthesized by spark plasma sintering

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB₂ superconductors