Enhancing superconducting properties of MgB₂pellets by addition of amorphous magnetic Ni–Co–B nanoparticles

Abstract

Amorphous magnetic Ni-Co-B nanoparticles with an average size of 5 nm were added to precursor powders of MgB2 superconductor. The preparation procedure for MgB2 pellets was optimized for obtaining the best critical current density ( Jc) at elevated magnetic fields. Addition of Ni-Co-B decreases the Jc for heat treatment of precursor powders at 650 ° C. Heat treatments at 770 ° C and higher improve Jc at 20 and 5 K. This improvement occurs at both temperatures through the increase of the effective connectivity between MgB2 crystals. Vortex pinning was enhanced at 5 K, but not at 20 K. Ni-Co-B nanoparticles reacted with Mg in heat treatments above 730 ° C, forming Mg2Ni and MgCo2 nanoparticles. Ni-Co-B addition was associated with lower oxygen content in MgB2, indicating that reduction of MgO content is the mechanism for improvement of grain connectivity. Decomposition of magnetic Ni-Co-B nanoparticles results mostly in nonmagnetic nanoparticles, so magnetic pinning did not occur in our samples.

Improvements in the Dispersion of Nanosilver in a MgB2 Matrix through a Graphene Oxide Net

“…10) show similarity with previous research on samples doped with Ni-Co-B nanoparticles 28,29,30 . All three observed curves have standard peaks associated with the melting of magnesium at 650ºC and the formation of MgB 2 at 750ºC.…”

Microstructural Features of Magnetic NiCoB Nanoparticles Addition to MgB2 Precursor Powders

“…It has been reported that the substitution of most doping elements on the Mg or B site lead to the suppression of Tc, [19] while the element and compound addition results in improvement of Jc, as mentioned earlier. Although there are some independent studies present, investigating the MgB2 samples with the performed addition of NiCoB nanoparticles, [20][21][22] they are mostly dealing with the effect of the addition of the nanoparticles on superconducting properties of MgB2. The microstructural analysis is mainly focused on the resulting MgB2 sample (formed after the addition of the nanoparticles to Mg and B precursor powders and sintering at various temperatures), [20] with relatively poor characterization of the identified constituent phases.…”

“…Although there are some independent studies present, investigating the MgB2 samples with the performed addition of NiCoB nanoparticles, [20][21][22] they are mostly dealing with the effect of the addition of the nanoparticles on superconducting properties of MgB2. The microstructural analysis is mainly focused on the resulting MgB2 sample (formed after the addition of the nanoparticles to Mg and B precursor powders and sintering at various temperatures), [20] with relatively poor characterization of the identified constituent phases. The characterization usually ends with quantitative analysis of the sample via Rietveld refinement (in form of obtained mass fractions of MgB2, MgO, and possible Mg if it is present).…”

“…The characterization usually ends with quantitative analysis of the sample via Rietveld refinement (in form of obtained mass fractions of MgB2, MgO, and possible Mg if it is present). [20,22] Even when the characterization of NiCoB nanoparticles (prior to the addition of Mg and B precursor powders) is present, there is no information about the size and shape of the phases that are formed from the starting nanoparticles (after the addition to Mg and B precursor powders and sintering at various temperatures). [21] The only information one can get is confirmation of their existence from XRD measurement without any quantitative data, such as their weight fraction.…”

“…Unfortunately, previous studies investigating the resulting MgB2 samples with the addition of magnetic nanoparticles did not make any correlations of the MgB2 crystallites size in these samples to the MgB2 crystallite size in the MgB2 samples without the addition (sintered with the same procedure as the resulting MgB2 samples with the magnetic nanoparticles, but without the addition of the nanoparticles). On contrary, either the sizes of the MgB2 crystallites in the resulting MgB2 sample (formed after the addition of the nanoparticles to Mg and B precursor powders and sintering at various temperatures) are given, [20] or they do not give any information about the sizes of the crystallites. [21,[23][24][25] The same stands for the MgB2 grain sizes determined from electron microscopy observation (mostly from SEM).…”