Silvana Mercone

Magnetization reversal behavior in complex shaped Co nanowires: A nanomagnet morphology optimization

A systematic micromagnetic study of the morphological characteristic effects over the magnetic static properties of Co-based complex shaped nanowires is presented. The relevance of each characteristic size (i.e. length L, diameter d, and size of the nanowires head T) and their critical values are discussed in the coercive field optimization goal. Our results strongly confirms that once the aspect ratio (L/d) of the nanowire is bigger than around 10, the length is no more the pertinent parameter and instead the internal diameter and the shape of the nanowires play a key role. We attribute this behavior to the non uniform distribution of the demagnetizing field which is localized in the nanowires head and acts as a nucleation point for the incoherent magnetization reversal. Finally, angular dependence of the magnetization are simulated and compared to the case of a prolate spheroid for all considered morphologies.

Real-Time Sensing of Enteropathogenic E. coli-Induced Effects on Epithelial Host Cell Height, Cell-Substrate Interactions, and Endocytic Processes by Infrared Surface Plasmon Spectroscopy

Enteropathogenic Escherichia coli (EPEC) is an important, generally non-invasive, bacterial pathogen that causes diarrhea in humans. The microbe infects mainly the enterocytes of the small intestine. Here we have applied our newly developed infrared surface plasmon resonance (IR-SPR) spectroscopy approach to study how EPEC infection affects epithelial host cells. The IR-SPR experiments showed that EPEC infection results in a robust reduction in the refractive index of the infected cells. Assisted by confocal and total internal reflection microscopy, we discovered that the microbe dilates the intercellular gaps and induces the appearance of fluid-phase-filled pinocytic vesicles in the lower basolateral regions of the host epithelial cells. Partial cell detachment from the underlying substratum was also observed. Finally, the waveguide mode observed by our IR-SPR analyses showed that EPEC infection decreases the host cells height to some extent. Together, these observations reveal novel impacts of the pathogen on the host cell architecture and endocytic functions. We suggest that these changes may induce the infiltration of a watery environment into the host cell, and potentially lead to failure of the epithelium barrier functions. Our findings also indicate the great potential of the label-free IR-SPR approach to study the dynamics of host-pathogen interactions with high spatiotemporal sensitivity.

Low Frequency Noise in High TC Ferromagnetic La2/3Sr1/3MnO3 Devices : Study of Anomalous Effects Below Curie Temperature

Manganite thin films showing colossal magnetoresistance, large resistance change at the metal-to-insulator (M-I) transition temperature and high spin polarization, are promising candidates for a new generation of electronic devices including magnetoresistive sensors, bolometers and spin-valve systems [1, 2, 3]. Among them, ferromagnetic La1 − x Sr x MnO 3 with x ∼ 0.3 (LSMO) attracts especially great attention due to its high Curie temperature value (T C ) of about 360 K, thus creating expectations for the realization of magnetic devices operating at room temperature. To study, understand and reduce the noise level of those compounds is a huge challenge. Here we report detailed investigations of 1/f electrical noise in structures patterned in epitaxial thin films of a large bandwidth La 2/3 Sr 1/3 MnO 3 (LSMO) deposited on (100) SrTiO 3 substrates. The 1/ f noise, which dominate along the whole range of frequencies studies, was observed not to follow the overall temperature dependence of the resistivity as shown by other LSMO film in literature [4]. Moreover no significant dependence of the 1/f noise with the temperature (above 300 K) could be observed, which seems to be in favor of a non magnetic origin of this noise. On the other hand at very low temperature (below 300 K-see pictures shown below), the application of a small magnetic field (i.e. 80 gauss) drives a very important change in a Lorentzian-like behavior appeared in our spectra. Although a direct correlation between noise and magnetoresistance can not be found out on our devices, a real discussion is open on the origin of this electrical fluctuation insight the Ferromagnetic state.