Mahipal Ranot

A simple method for the enhancement of Jc in MgB2 thick films with an amorphous SiC impurity layer

We investigated the effect of SiC doping on the critical current density (Jc) in MgB2 thick films using amorphous SiC impurity layers of various thicknesses: 7, 14, 35, and 70?nm. SiC impurity layers were first deposited on the Al2O3(0001) substrates at room temperature by using a pulsed laser deposition system, after which MgB2 films were grown on the SiC deposited precursor substrates by using a hybrid physical?chemical vapor deposition technique at a low growth temperature of 480??C. All samples showed a high transition temperature of ~40?K irrespective of the thickness of the impurity layer. The grain sizes of the MgB2 films slightly increased from 400 to 488?nm with increasing thickness of the impurity layer. The MgB2 thick film with a 35?nm thick SiC impurity layer exhibited the highest Jc, while all SiC doped samples showed a higher Jc than a pure MgB2 thick film throughout the whole magnetic field region. These results suggest that the SiC particles of the impurity layer diffused into the MgB2 films during film growth, and the SiC particles, along with the columnar grain boundaries in the MgB2 thick films, act as strong pinning centers.

Superconducting MgB2 flowers: growth mechanism and their superconducting properties

We report for the first time the growth and the systematic study of the growth mechanism for flower-like MgB2 structures fabricated on the substrates for solid-state electronics by the hybrid physical-chemical vapor deposition (HPCVD) technique. The MgB2 flower has a width of 30 μm and a height of 10 μm. The superconductivity of MgB2 flowers was confirmed by a magnetization measurement, and the transition temperature is 39 K, which is comparable with high-quality bulk samples. The excellent current-carrying capability was demonstrated by MgB2 flowers. To understand the nucleation and growth mechanism of MgB2 flowers a very systematic study was performed by a high-resolution transmission electron microscope (HRTEM) and atom probe (AP) microscopy. The HRTEM revealed that the seed grain of a MgB2 flower has a [100] direction, and the flower is composed of micro-columnar MgB2 grains having pyramidal tips and which are grown along the (0001) plane. A clear understanding of the growth mechanism for MgB2 flowers could lead to the growth of other low-dimensional MgB2 structures for superconducting electronic devices.

Effect of Different Thickness Crystalline SiC-Buffer Layers on Superconducting Properties and Flux Pinning Mechanism of

We have fabricated the superconducting MgB2 films grown on three different crystalline SiC-buffer layers of different thickness by means of the hybrid physical-chemical vapor deposition technique and pulsed laser deposition method. Significant changes in the microstructural and superconducting properties of MgB2 films with addition of crystalline SiC-buffer layers were observed. The microstructural analyses of MgB2 films revealed that columnar grains were formed perpendicularly to the substrates, thus, enhancing all critical current density values at 5 and 20 K for all SiC-buffered-MgB2 films. The scaling behavior of the flux pinning force shows a magnetic field-dependent feature with different pinning mechanisms, from which one can infer that there are additional pinning centers that exist in the samples and cannot be interpreted by a simple superposition of different types of elementary pinning sources.