Dipak Kumar Baisnab

Intricacies of strain and magnetic field induced charge order melting in Pr0.5Ca0.5MnO3 thin films

Thin films of the half-doped manganite Pr0.5Ca0.5MnO3 were grown on (1 0 0) oriented MgO substrates by pulsed laser deposition technique. In order to study the effect of strain on the magnetic field induced charge order melting, films of different thicknesses were prepared and their properties were studied by X-ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thicknesses. The charge order transition temperature and the magnetic field induced charge order melting are observed to depend on the nature of strain that is experienced by the film.

Increased upper critical field for nanocrystalline MoN thin films deposited on AlN buffered substrates at ambient temperature

Molybdenum nitride (MoN) thin films have been deposited using reactive DC magnetron sputtering on aluminum nitride buffered oxidized silicon substrates at ambient temperature. GIXRD of aluminum nitride (AlN) deposited under similar conditions has revealed the formation of wurtzite phase AlN. GIXRD characterization of molybdenum thin films deposited on AlN buffered oxidized silicon substrates has indicated the formation of nanocrystalline MoN thin films. The electrical resistivity measurements indicate MoN thin films have a superconducting transition temperature of ~8 K. The minimum transition width of the MoN thin film is 0.05 K at 0 T. The inferred upper critical field B c2(0) for these nanocrystalline MoN thin films obtained by fitting the temperature dependence of critical field with Werthamer, Helfand and Hohenberg theory lies in the range of 17–18 T which is the highest reported in literature for MoN thin films.

Evolution of ferromagnetic clustering in Pr0.5Ca0.5MnO3 and its effect on the critical temperature of YBa2Cu3O7 thin film

A thin film bilayer of Pr0.5Ca0.5MnO3 and YBa2Cu3O7 has been deposited on LaAlO3 substrate by pulsed laser deposition. XRD pattern confirms the formation of the bilayer. Current and magnetic field dependent resistance measurements have been carried out to study the proximity effect. These measurements have shown that the superconducting transition temperature (Tc) of YBa2Cu3O7 is suppressed to lower temperatures with a progressive increase in current. In addition, a hump like feature appears in resistivity near Tc with increase in applied current. The results are explained on the basis of the formation and growth of ferromagnetic clusters on account of charge order melting in Pr0.5Ca0.5MnO3 upon application of high current and magnetic field.

Development of High Tc Superconducting Quantum Interference Devices

SQUID sensors based on High Temperature Superconductors (HTS) have been designed and fabricated. The devices were fabricated using highly reliable advanced micro‐fabrication techniques such as deposition of superconducting thin films by Pulsed Laser Deposition (PLD), UV photolithography and RF ion beam etching. Microbridges patterned across a bicrystal boundary or an artificially created step‐edge served as Josephson weak links. Two designs, differing in the placement of Josephson weak links relative to the sensing area, were tested. Some of the devices yielded a voltage modulation depth in excess of 100 μV. These developments augur well for a more widespread use of SQUID sensors since these can be operated at liquid nitrogen temperatures, making a field deployment relatively easier.

Development of planar first order gradiometer coupled to HTS SQUID sensor

The HTS SQUID sensors coupled to an on-chip integrated planar gradiometric pick-up loop were fabricated using highly reliable advanced micro-fabrication techniques such as deposition of superconducting thin films by Pulsed Laser Deposition (PLD), UV photolithography and RF ion beam etching. It may be noted that use of wire wound gradiometers and approaches based on electronic subtraction of sensor outputs to realize synthetic gradiometers have not been entirely satisfactory. We have designed a first order planar gradiometer with two planar loops in opposition with the Josephson weak links in the form of microbridges located at the centre. Bicrystal SrTiO3 substrates with a 24° misorientation angle were used for realizing the Josephson weak links using YBCO thin films, as well as HTS planar gradiometer coupled to a HTS SQUID sensor. The performance of these devices are evaluated.

The effects of strain, current, and magnetic field on superconductivity in Pr0.5Ca0.5MnO3/YBa2Cu3O7/Pr0.5Ca0.5MnO3 trilayer

Thin film trilayers of Pr0.5Ca0.5MnO3/YBa2Cu3O7/Pr0.5Ca0.5MnO3 have been deposited on MgO substrate by pulsed laser deposition technique. The film thicknesses were selected so that in one of the trilayers, the bottom Pr0.5Ca0.5MnO3 layer is thin, and hence, subjected to substrate induced strain, while in another trilayer, the bottom layer is sufficiently thick to ensure that it is not subjected to such strain. Current and magnetic field dependent resistance measurements have been carried out on the trilayers down to liquid helium temperatures to investigate the influence of charge-order melting and the consequent formation of ferromagnetic clusters in the Pr0.5Ca0.5MnO3 film on the superconducting properties of YBa2Cu3O7. These measurements show that the suppression of the superconducting transition temperature (Tc) of YBa2Cu3O7 is relatively high for the strained trilayer compared to that observed for the other. The activation energy for hopping of vortices in the sandwiched YBa2Cu3O7 film was estimated ...

Effect of current induced charge-order melting of Pr0.5Ca0.5MnO3 in partially masked superconducting Pr0.5Ca0.5MnO3/YBa2Cu3O7 bilayer

In order to investigate the effect of current induced charge-order melted ferromagnetic Pr0.5Ca0.5MnO3 on superconducting YBa2Cu3O7, current and magnetic field dependent resistance measurements have been carried out in Pr0.5Ca0.5MnO3/YBa2Cu3O7 thin film heterostructure in which a part of the YBa2Cu3O7 thin film is covered by Pr0.5Ca0.5MnO3. The measurements show that superconducting transition temperature of the uncovered YBa2Cu3O7 is suppressed to lower temperatures with a progressive increase in current. Results show the possibility of controlling the superconducting properties of the uncovered part of the YBa2Cu3O7 thin film by influencing the part covered by Pr0.5Ca0.5MnO3.

Effect of current induced charge order melting of Pr0.5Ca0.5MnO3 on YBa2Cu3O7 thin film

A thin film bilayer of Pr0.5Ca0.5MnO3 and YBa2Cu3O7 has been deposited on LaAlO3 substrate by pulsed laser deposition. X-ray diffraction analysis confirms the formation of the bilayer. Current dependent magnetoresistance measurements show that the superconducting transition temperature (Tc) of YBa2Cu3O7 is suppressed to lower temperatures and a hump like feature appears in resistivity near Tc with increase in measuring current. The results are explained on the basis of formation of ferromagnetic clusters upon application of high current and magnetic field.

Strain enhanced charge order melting in Pr0.5Ca0.5MnO3 thin films

The effect of strain on charge order melting in half doped manganite Pr0.5Ca0.5MnO3 thin films of different thicknesses has been investigated. The films were deposited on (100) oriented MgO substrates by pulsed laser deposition technique and were characterized by x‐ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thickness. The charge order transition temperature and the magnetic field induced charge order melting appears to be governed by the nature of strain that is experienced by the film.