<p class="p1"> <strong>RESUMEN: </strong>El Laboratorio Nacional de Nanotecnología (nanotech) inicia sus actividades a partir de 2006, gracias a un financiamiento por 20 millones de pesos del CONACYT. El interés principal de este laboratorio es ampliar las capacidades de síntesis, evaluación y caracterización de nanomateriales (tanto metálicos como orgánicos), la infraestructura generada desde su creación le ha permitido llegar a este nivel. El equipamiento incluye desde microscopios de alta resolución, microscopios para las ciencias de la vida y otros que los complementan. Dado que la nanotecnología es ahora una prioridad en investigación para nuestro país, un laboratorio de estas características se vuelve de suma importancia a nivel nacional, al formar parte de una red de IES y Centros Públicos capaces de atender y ayudar a las diferentes áreas del conocimiento y al sector industrial y gubernamental. </p>

SmCo/FeCo/SmCo trilayer was deposited with two different thickness configurations for soft phase (FeCo); 50 nm/10 nm/50 nm and 50 nm/25 nm/50 nm were deposited on Si (111) substrate and Ta (50 nm) seed layer by RF magnetron sputtering in a pressure, p, of 30 -35 m Torr. After deposition the films were annealed under Ar atmosphere at temperature T equal to 923 and 973 for different times followed by quenching in water. X-ray diffraction patterns were obtained to identified phase presents and calculate average crystallite size. To study the effect of configuration thickness in soft phases, DC magnetic measurements were carried out; the measurements were done in the temperature interval of 300 -50 K. Hysteresis loops collected at low temperatures exposed an increment in coercivity with the decrease of T and at same time, presented a "knee" in the second quadrant of the demagnetization curve, which suggests that the inter-layer exchange coupling becomes less effective, being more evident for sample with 50 nm/25 nm/50 nm thickness. Moreover, δM (H) plots were calculated from magnetic measurements at three different temperatures, T, equal to 300, 150 and 50 K, which corroborates that the dipolar interactions became stronger when thickness of soft phases increases. Finally, the thickness effect is attributed to the SmCo5 phase magnetocrystalline anisotropy constant, which is responsible for the exchange coupling length.

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The use of rechargeable batteries has become a standard for mobile applications being, for many years, LiCoO 2 the most common material used for the cathode. However, the toxicity of cobalt and its high cost has stimulated the search of alternative materials to substitute cobalt by a cheaper and environmental friendly material. One of the most promissory materials to fulfill these requirements is the spinel LiMn 2 O 4 . Recently, several new spinel manganates, where the Mn 16d site of the spinel structure is partially substituted by a third cation, have been studied extensively. These materials overcome the disadvantages of stoichiometric spinel LiMn 2 O 4 and still posses a spinel structure. In this work, the dielectric properties of LiMn 2 O 4 and LiMn 1.5 Ni 0.5 O 4 powders, synthesized by sol-gel method, were determined by analyzing the low loss region of the EELS spectrum in a transmission electron microscope. These spectra can be interpreted on the basis of ab initio calculations. Theoretical calculations are based on the pseudo-potential plane-wave method within the framework of the density functional theory (DFT), as implemented in CASTEP code. Norm-conserving pseudopotentials were employed to describe the electron-ion interactions. The exchange and correlation terms were described with the generalized gradient approximation (GGA). An energy cutoff E cut = 550 eV was chosen, and self-consistency was considered to be achieved when the total energy variation from iteration to iteration did not exceed 5x10 -7 eV/atom. For the substituted spinel LiMn 1.5 Ni 0.5 O 4 a 2x1x1 supercell was constructed. The crystal structures of the lithium manganate spinel and substituted spinel were taken from experimental results. Electron energy loss spectra were obtained using a Gatan Parallel Electron Energy Loss Spectrometer (PEELS model 766) attached to a Philips CM-200 transmission electron microscope. Spectra were acquired in diffraction mode with 0.2 eV/ch dispersion, an aperture of 2 mm and a collection semi-angle of about 2.7 mrad. The resolution of the spectra was determined by measuring the full width at half-maximum (FWHM) of the zero loss peak and this was typically close to 1.2 eV, when the TEM was operated at 200 kV. EELS spectra were corrected for dark current and readout noise. The channel to channel gain variation was minimized by normalizing the experimental spectrum with independently obtained gain spectrum of the spectrometer.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.