Abstract
Flux pinning force scaling f=F_{p}/F_{p,max limits } vs. h = Ha/Hirr was performed on a variety of pure MgB2 samples, including a spark plasma sintered (SPS) one and a series of samples sintered at various reaction temperatures ranging between 775 and 950 ∘C. The SPS sample exhibits a well-developed scaling at all temperatures, and also the sintered samples prepared at 950 ∘C; however, the obtained peak positions of the pinning force scalings are distinctly different: The SPS sample reveals dominating pinning at grain boundaries, whereas the dominating pinning for the other one is point-pinning. All other samples studied reveal an apparent non-scaling of the pinning forces. The obtained pinning parameters are discussed in the framework of the Dew–Hughes’ pinning force scaling approach.
Highlights
The MgB2 superconductors are interesting for various applications as they offer the metallic character which enables a simple processing route and no involved rare earth materials, which reduces the costs involved [1, 2]
To obtain information on the flux pinning in MgB2 samples, we investigated a pure spark plasma sintered (SPS)-produced MgB2 sample with its high density close to the ideal value, and several members of a series of sintered, polycrystalline MgB2 samples prepared at various reaction temperatures ranging between 775 and 950 ◦C
The sample preparation steps for the SPS sample are described in Ref. [22, 23], and the fabrication of the polycrystalline, sintered samples is discussed in Ref. [24]
Summary
The MgB2 superconductors are interesting for various applications as they offer the metallic character which enables a simple processing route and no involved rare earth materials, which reduces the costs involved [1, 2]. The modern cryocooling techniques enable a temperature of 20 K to be reached, which is commonly accepted as the optimum one for applications of MgB2 Besides these advantages, the still limited critical current densities and the presence of flux jumps require further studies on the acting flux pinning mechanism(s) in MgB2 superconductors [3,4,5,6,7,8,9,10]. The pinning force scaling as introduced by Kramer [11] and Dew–Hughes (DH) [12] is an important tool to study the pinning mechanisms acting in a given superconductor sample This applies for the conventional metallic superconductors, where the pioneering work was performed
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