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Department of Chemistry, CMR Institute of Technology, 132 AECS layout, Bangalore-560 037, India E-mail : chaitanya.l@cmrit.ac.in NNL CNR-Istituto Nanoscienze, Via Per Arnesano, 73100 Lecce, Italy Department of Mathematics and Physics “Ennio de Giorgi”, University of Salento, Via Per Arnesano, 73100 Lecce, Italy Integrating nanocrystals (NCs) into magnetic tunnel structures is of considerable interest due to expectation of novel properties from their spin selective transport and single electron features. Superstructures by colloidal NCs having translational and orientational order and interesting collective magnetic properties can be prepared by solution casting through sensitive interparticle and particle-substrate interactions. In this work, we discuss the study on magnetic field induced assembly of mono-dispersed iron oxide NCs to obtain spin filter effect across the superlattice array, when sandwiched between gold electrodes. The deposition of mixed phase Fe3O4@γ-Fe2O3 NCs on SiO2 /Au surface proceeds through slow solvent evaporation and are studied for controlled interparticle spacing. For specific NC concentration, the ordering depends on the substrate chemistry and the ligands passivating NC surface, which affects the concentration of cluster nuclei formed. In presence of a magnetic field, the tunnel structure exhibits enhanced positive tunnel magnetoresistance at low temperatures, which could be related to their ferromagnetism and the attempts by electrons to percolate NC superlattice with preserved spin. A sign reversal for magnetoresistance is exhibited by the vertical tunnel junctions on raising the temperature.

The dielectric properties of YCTO bulk capacitors were investigated as a function of temperature from 25 degrees C to 150 degrees C and at microwave frequencies in comparison to a SiO2 bulk sample. The results confirm the high-k character of the YCTO ceramic, in addition to the low AC conductivity, namely epsilon' = 40.1 and sigma = 6 x 10(-8) S cm(-1) at 1 MHz, and show a weak frequency and temperature (25 degrees C-150 degrees C) dependence. A temperature coefficient value of -601 ppm degrees C-1 for the dielectric constant (TC epsilon') was estimated at 100 kHz. In the GHz regime, a comparison with bulk SiO2 confirms the higher YCTO dielectric permittivity. These results demonstrate high-k YCTO ceramic as a very promising material with high potentiality for electronic applications.

The increasing constraints in the miniaturization of modern electronic devices is driving the search for new high-k dielectric materials. Rare-earth transition metal oxides are very interesting because of the large values of dielectric constant observed in bulk samples. Here, we report on a comparison among the dielectric properties of yttrium copper titanate (YCTO) thin films and those of commonly used dielectrics such as SiO2 and MgO, grown in similar device structures. The YCTO permittivity was found to depend strongly on the oxygen pressure during deposition and can reach values even higher than those reported in bulk YCTO with good performances in terms of losses.

The high permittivity values reported in rare-earth transition metal oxides ceramics makes them very interesting as alternative gate dielectrics. Here, we summarize our recent results on the yttrium copper titanate (YCTO) thin films under different deposition conditions. Their dielectric properties were studied both in metal-oxide-metal (MIM) and in metal-oxide-semiconductor (MOS) junctions for respectively investigating the material response without parasitic substrate contributions and evaluating the YCTO performance as gate oxide. A strongly dependence of the permittivity from deposition conditions was observed, with a variation from 100 down to 24 at 100 kHz. Such behavior was ascribed to film microstructure variations. Notably, at certain deposition conditions, YCTO thin films possess a higher dielectric permittivity than their bulk counterpart (40.3) in addition to good performances in term of losses. These results demonstrate the applicability of YCTO as alternative high-k gate oxides.