The effect of nano-alumina on structural and magnetic properties of MgB₂superconductors

Abstract

Nano-Al2O3 doped Mg1−xAlxB2 with 0≤x≤6% were synthesized by solid state reaction at 750 °C in Fe tube encapsulation under a vacuum of 10−5 Torr. Resistance measurement shows that the Tc decreases with x and zero resistivity for x = 0 and 6% are obtained at 38 and 35 K, respectively. XRD measurement shows that the lattice parameter and cell volume also decrease monotonically with increasing doping levels. From this we infer that the Al has been substituted in the lattice of MgB2 at Mg sites. Resistivity measurement shows a systematic decrease in Tc with doping which also confirms the substitution of Al. Magnetization studies in the temperature range from 4 to 35 K and in the magnetic field up to 9 T shows a significant increase in the irreversibility field (Hirr), critical current density (Jc) and remanent magnetization (MR) with increasing concentration of the Al2O3 nanoparticle. At low fields we have observed large vortex instabilities (known as a vortex avalanche) associated with all doped samples. The vortex-avalanche effect is reduced with increasing temperature and vanishes near 20 K. The results are discussed in terms of local-vortex instabilities caused by doping of Al2O3 nanoparticles.

Superconducting transition width under magnetic field in MgB2 polycrystalline samples

“…For example, in the SiC-doped and C-doped samples, the SiC-doping and C-doping allows C substitution for boron, 21 whiles in the Al 2 O 3 -doped sample, Mg replaced by Al was widely reported. 22,23 Although in SiO 2 -doped sample, Si is doped into the MgB 2 lattice cell leading to the formation of Mg 2 Si particles, 24 SiO 2 is regarded as a real impurity like MgO, which deteriorates the superconductivity by changing the microstructure and the grain connectivity. 25 The addition of Si 3 N 4 also led to the formation of Mg 2 Si, which is similar to the results of most other silicon compounds doping.…”

Calculation of Normalized Pinning Force and Nature of Pinning Mechanism for Nano-Al Doped MgB2 Superconductor

“…In order to further find out evidences, the magnetic field dependence of Jc at different temperature has been calculated under different doping level. [6] ), there are some jumps reflected at 10K (nearby 1T) and 20K (nearby 3.5T) for 6% doped and pure sample, respectively as shown in the Figure 4. In addition, at 30K temperature the 4% and 6% Al doped sample depicts some jumps as well close to 0.25T field.…”

“…The present study described the detailed analysis of the Jc and normalized pinning force, f as a function of magnetic field and temperature for nano Al doped MgB2 sample using the simple scaling law described above. The difference between the previous report [6] and present is that in the prior report only magnetic behavior have been analyzed but in the present report I have calculated the Jc as well as the pinning mechanism for nano Al doped MgB2. In order to examine the dominant pinning mechanism for nano Al doped MgB2 sample this scaling law describes the significant results.…”

“…%) were synthesized by in-situ standard solid state reaction method under high vacuum as described elsewhere in detail [6]. The starting material powders (purity > 99%) were mixed in the stoichiometric ratio supplied by SigmaAldrich.…”

Enhancement of critical current density for nano (n)-ZnO doped MgB2 superconductor

“…Enormous efforts have been made on the way to the fabrication of high-quality MgB 2 superconductor. In order to enhance the J c , H c2 , and the irreversibility field (H irr ), enormous chemical doping [13][14][15][16][17][18][19][20][21], different routes [22][23][24][25], and thermo-mechanical processing techniques [26,27] have been adopted. Remarkably, chemical doping particularly using nano-particle doping has revealed the great promise in improving the J c -H behavior due to form a high density of nano-inclusions in MgB 2 matrix and provides a strong flux pinning force (F p ).…”