Dr. Gustavo Grinblat received his Masters in Physics degree at the Balseiro Institute, Bariloche (Argentina) in 2010 and since March 2011 is a NanoProject Group member at the Faculty of Exact Sciences and Technology, National University of Tucuman as a PhD Student under Dr. David Comedi's guidance and Dr. Andrea Bragas (LEC, Dep. Physics, FCEN, National University of Buenos Aires) co-guidance (Graduated From the University of Buenos Aires in May 2015). His main research project is on the Linear and Nonlinear Optical Properties of Semiconductor Nanostructures.
"I performed my master’s thesis at the Low Temperature Lab, in the Bariloche Atomic Center, Argentina, under Dr. Julio Guimpel's guidance. We have studied Nb/Co (Superconductor/Ferromagnet) superlattices with different periodicity, fabricated through dc Magnetron Sputtering technique in an Ar plasma. We have used superlattices with Nb layers less than 50nm thick, and Co up to 2nm.
We have worked at the nanometer scale for the proximity effect that occurs when these materials are brought intimately together to be significant. Through AC magnetic susceptibility and electric transport measurements, we have studied the character of the superconducting layers coupling as a function of the Co films thickness (dCo). We have found that the coupling is strong for dCo = 0.5nm, and that the superconducting layers behave as decoupled when dCo = 1.5nm. For intermediate thicknesses the coupling is weak.
We have done this study by characterizing the upper critical field temperature dependence, for different configurations of the applied magnetic field (H) with respect to the sample. We analyzed the results in terms of the Ginzburg-Landau theory, for the thin superconducting film case.
If H is perpendicular to the layers of a superlattice, the superconducting vortices that are generated present translational symmetry in the plane defined by the sample surface. On the contrary, if H is applied parallel to the layers direction, then, due to the presence of the Co films and the finite size effects, the mobility of the vortices is strongly affected.
In this last configuration, if the superconducting layers are weakly coupled, then the Co films will serve as correlated pinning centers for the vortices. Through critical current measurements in a four probe geometry, we have found a non-trivial behavior of the pinning mechanisms, which is also evident in the dissipation measured by AC susceptibility.
These characteristics could be indicators of structural transitions of the vortex lattice, due to the interaction between the vortices, the pinning in the correlated pinning centers and the surface Meissner currents."
"The above is a copy of a poster with some important results of a Nb/Co superlattice, which I presented at the Giambiagi Winter School in Buenos Aires , Argentina, in 2010. This sample presents weak coupling between the superconducting layers, which is the most interesting case. "
Dr. Grinblat's selected papers:
G. Grinblat, M. Rahmani, E. Cortés, M. Caldarola, D. Comedi, S. A. Maier, A. Bragas, High efficiency second harmonic generation from a single hybrid ZnO nanowire/Au plasmonic nano-oligomer, Nano Letters 14, 6660-6665 (2014).
G. Grinblat, F. Bern, J. Barzola-Quiquia, M. Tirado, D. Comedi, P. Esquinazi, Luminescence and electrical properties of single ZnO/MgO core-shell nanowires, Applied Physics Letters 104, 103113 (2014).
G. Grinblat, L.J. Borrero González, L.A.O. Nunez, M. Tirado, D. Comedi, Enhanced optical properties and (Zn,Mg) interdiffusion in vapour transport grown ZnO/MgO core/shell nanowires, Nanotechnology 25, 035705 (2014).
G. Grinblat, M.G. Capeluto, M. Tirado, A.V. Bragas, D. Comedi, Hierarchichal ZnO nanostructures: Growth mechanisms and surface correlated photoluminescence, Appl. Phys. Lett. 100, 233116 (2012).