http://dspace-roma3.caspur.it:80 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Thu, 20 Jun 2013 05:58:38 GMT 2013-06-20T05:58:38Z http://dspace-roma3.caspur.it/image/logo_roma3.jpg http://dspace-roma3.caspur.it:80 http://hdl.handle.net/2307/380 <Title>Reduction in the field-dependent microwave surface resistance inYBa2Cu3O7-delta with submicrometric BaZrO3 inclusions as a function of BaZrO3 concentration</Title> <Authors>Pompeo, Nicola; Rogai, Raffaella; Augieri, A.; Galluzzi, V.; Celentano, G.; Silva, Enrico</Authors> <Issue Date>2009-01-15</Issue Date> <Is part of>Journal of applied physics</Is part of> <Volume>105</Volume> <Pages>013927-013927-7</Pages> <Abstract>In order to study the vortex pinning determined by artificiallyintroduced pinning centers in the small-vortex displacement regime, wemeasured the microwave surface impedance at 47.7 GHz in the mixed stateof YBa2Cu3O7-delta thin films, where submicrometric BaZrO3 particleshave been incorporated. As a function of the BaZrO3 content, weobserved that the absolute losses slightly decrease up to a BaZrO3content of 5%, and then increase. We found that themagnetic-field-induced losses behave differently in that they are notmonotonic with increasing BaZrO3 concentration. At small concentration(2.5%) the field-induced losses increase, but large reduction in thelosses themselves, by factors up to 3, is observed upon furtherincreasing the BaZrO3 concentration in the target up to 7%. Usingmeasurements of both surface resistance and surface reactance, weestimate vortex pinning-related parameters. We found that BaZrO3inclusions introduce deep and steep pinning wells. In particular, theminimum height of the energy barrier for single vortices is raised. Atlarger BaZrO3 content (5% and 7%) the phenomenon is at its maximum, butit is unclear whether it shows a saturation or not, leaving room forfurther improvements. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3056179]</Abstract> Wed, 14 Jan 2009 23:00:00 GMT http://hdl.handle.net/2307/380 2009-01-14T23:00:00Z http://hdl.handle.net/2307/382 <Title>Effect of BaZrO3 Inclusions on the Microwave Surface Impedance of YBCOFilms in a Magnetic Field</Title> <Authors>Pompeo, Nicola; Rogai, Raffaella; Galluzzi, Valentina; Augieri, Andrea; Celentano, Giuseppe; Ciontea, Lelia; Petrisor, Traian; Silva, Enrico</Authors> <Issue Date>2009-07-15</Issue Date> <Is part of>IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY</Is part of> <Volume>19</Volume> <Pages>2917-2920</Pages> <Abstract>We perform measurements of high-frequency (similar to 48 GHz) microwavesurface impedance with an applied magnetic field in YBa2Cu3O7-delta (YBCO) laser-ablated films with various amounts of BaZrO3 ( BZO)sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusionsare very effective in the reduction of the field-induced surfaceresistance in our experimentally accessible field range [ 0, 0.8] T. Attemperatures low enough, the application of a moderate (similar to 0.2T) field makes the YBCO/BZO films markedly less dissipative than pureYBCO. This result, examined in the light of the very high measuringfrequency ( very small vortex oscillation amplitude) shows that BZOinclusions are even more effective pinning centers than columnardefects. We study the dependence of the vortex parameters ( vortexviscosity, pinning constant) on the BZO concentration. We examine thecorrelation between the reduction of the microwave dissipation and theareal density of BZO-induced defects. We argue that the very improvedperformances in a magnetic field are due to individual pinning ofvortices on BZO inclusions.</Abstract> Tue, 14 Jul 2009 22:00:00 GMT http://hdl.handle.net/2307/382 2009-07-14T22:00:00Z