Surface behavior of La2/3Ca1/3MnO3 epitaxial thin films

The role of the surface layers in La2/3Ca1/3MnO3 magnetic oxide epitaxialthin films is analyzed. We show that the topmost layers do play a very relevant role on the transport properties acting as an insulating barrier. Atomic force microscopy(AFM)measurements in the current sensing mode exhibit typical features of tunneling conduction. The analysis of the I-V curves by using the Simmons model give values of barrier thickness in good agreement with nonmagnetic layer thickness estimates from magnetic measurements.Ex situannealing in air at high temperature clearly improve the magnetotransport properties of the films reducing the surface insulating barrier

Polarization reconfigurable MEMS-CPW antenna for mm-wave applications

This letter presents a polarization reconfigurable MEMS-integrated coplanar patch antenna for mm-wave applications. The polarization of the field radiated by this reconfigurable antenna can be configured into right-handed circular polarization (RHCP), left-handed circular polarization (LHCP) or linear polarization (LP). This is accomplished by the activation/deactivation of RF-MEMS switches. The consistency of the simulated results was successfully checked with measurements.Peer ReviewedPostprint (published version

60GHz channel characterization using a Scatterer Mapping Technique

In this paper, a Scatterer Mapping Technique based on a Multi-Frequency Bi-focusing operator with good imaging capabilities is used to characterize the 60GHz wireless channel in an office environment. The measurement data is also processed to extract the effective number of communication channels. The relation between the 60GHz office scatterer map and the effective number of communication channels is highlighted.Peer ReviewedPostprint (published version

Structure and magnetic properties of Co-doped ZnO nanoparticles

In this work we carefully analyze the role of the microstructure on the magnetic properties of Co-doped ZnO nanoparticles prepared by the vaporization-condensation method in a solar reactor. We show that a close correlation exists between microstructural features and the appearance of ferromagnetism. Both shape and size of the particles, as well as the microstructure, can be controlled by changing the pressure inside the evaporation chamber, as evidenced by transmission electron microscopy micrographs and high resolution electron microscopy HREM. X-ray diffraction patterns and HREM make evident the absence of any significant Co segregation or any other phase different from würtzite type ZnO. On the other hand, electron energy loss spectroscopy analyses performed on several particles of würtzite type ZnO yielded an average Co concentration in good agreement with the nominal composition. Samples prepared in low pressure 10 Torr exhibit a very homogeneous microstructure and are ferromagnetic at low temperature but they have a very small saturation moment, well below that expected for a Co2+ ion. Conversely, samples prepared at higher pressure conditions 70–100 Torr show a defective microstructure and are paramagnetic and increasing the Co content does not induce ferromagnetism

Role of the microstructure on the magnetic properties of Co-doped ZnO nanoparticles

We report on the magnetic and structural properties of Co-doped ZnO nanoparticles prepared by the vaporization-condensation method in a solar reactor. X-ray diffraction data and high-resolution electron microscopy (HREM) confirm the total absence of metallic Co clusters or any other phase different from würtzite-type ZnO.Electron energy loss spectroscopy analyses performed on several particles indicate that the oxidation state of Co is +2 and yield an average Co concentration of 4.5at.%, in good agreement with the nominal composition. Transmission electron microscopy micrographs show that shape and size of the particles are strongly dependent on the preparation conditions, as well as the microstructure as evidenced by HREM. Ferromagnetism is only found in samples prepared in vacuum revealing a close correlation between microstructure and magnetic properties

Perpendicular magnetic anisotropy in chemically disordered FePd-FeV(100) alloy thin films

We find that the use of V(100) buffer layers on MgO(001) substrates for the epitaxy of FePd binary alloys yields to the formation at intermediate and high deposition temperatures of a FePd¿FeV mixed phase due to strong V diffusion accompanied by a loss of layer continuity and strong increase of its mosaic spread. Contrary to what is usually found in this kind of systems, these mixed phase structures exhibit perpendicular magnetic anisotropy (PMA) which is not correlated with the presence of chemical order, almost totally absent in all the fabricated structures, even at deposition temperatures where it is usually obtained with other buffer layers. Thus the observed PMA can be ascribed to the V interdiffusion and the formation of a FeV alloy, being the global sample saturation magnetization also reduced

Tunneling anisotropic magnetoresistance in La2/3Sr1/3MnO3/LaAlO3/Pt tunnel junctions

The magnetotransport properties of La2/3 Sr1/3 MnO3 (LSMO)/ LaAlO3 (LAO)/Pt tunneling junctions have been analyzed as a function of temperature and magnetic field. The junctions exhibit magnetoresistance (MR) values of about 37%, at H=90 kOe at low temperature. However, the temperature dependence of MR indicates a clear distinct origin than that of conventional colossal MR. In addition, tunneling anisotropic MR (TAMR) values around 4% are found at low temperature and its angular dependence reflects the expected uniaxial anisotropy. The use of TAMR response could be an alternative of much easier technological implementation than conventional MTJs since only one magnetic electrode is required, thus opening the door to the implementation of more versatile devices. However, further studies are required in order to improve the strong temperature dependence at the present stage

Macromolecular crowding upon in-vivo-like enzyme-kinetics: effect of enzyme-obstacle size ratio

In the present work, the volume exclusion phenomenon, also known as macromolecular crowding, has been applied to the field of enzyme kinetics. It has been approached by adding polymeric obstacles in the media of different enzymatic reactions. The concentration and size of these obstacles have been changed systematically in order to obtain kinetic information about each reaction. Results indicate that the performance of a certain enzyme always depends on the amount of excluded volume. However, only large, oligomeric proteins display an obstacle size-dependent behavior. Besides, crowding can hinder diffusion to the extent of being capable of shifting reaction control from activation to diffusion