arXiv subjects

A. Serrano

Publications and source records attributed to A. Serrano.

11 recordsLinked to original sources

arXiv2023

Quantifying Li-content for compositional tailoring of lithium ferrite ceramics

Owing to their multiple applications, lithium ferrites are relevant materials for several emerging technologies. For instance, LiFeO2 has been spotted as an alternative cathode material in Li-ion batteries, while LiFe5O8 is the lowest damping ferrite, holding promise in the field of spintronics. The Li-content in lithium ferrites has been shown to greatly affect the physical properties, and in turn, the performance of functional devices based on these materials. Despite this, lithium content is rarely accurately quantified, as a result of the low number of electrons in Li hindering its identification by means of routine materials characterization methods. In the present work, magnetic lithium ferrite powders with Li:Fe ratios of 1:1, 1:3 and 1:5 have been synthesized, successfully obtaining phase-pure materials (LiFeO2 and LiFe5O8), as well as a controlled mixture of both phases. The powders have been compacted and subsequently sintered by thermal treatment (Tmax = 1100 {\deg}C) to fabricate dense pellets which preserve the original Li:Fe ratios. Li-content on both powders and pellets has been determined by two independent methods: (i) Rutherford backscattering spectroscopy combined with nuclear reaction analysis and (ii) Rietveld analysis of powder X-ray diffraction data. With good agreement between both techniques, it has been confirmed that the Li:Fe ratios employed in the synthesis are maintained in the sintered ceramics. The same conclusion is drawn from spatially-resolved confocal Raman microscopy experiments on regions of a few microns. Field emission scanning electron microscopy has evidenced the substantial grain growth taking place during the sintering process - mean particle sizes rise from about 600 nm in the powders up to 3.8(6) um for dense LiFeO2 and 10(2) um for LiFe5O8 ceramics.

cond-mat.mtrl-sci↗

arXiv2022

Effect of annealing in the formation of well crystallized and textured SrFe$_{12}$O$_{19}$ films grown by RF magnetron sputtering

We have studied the influence of annealing treatment on the crystalline growth of SrFe_12_O_19 previously deposited on Si (100) substrates using radio frequency (RF) magnetron sputtering. For this goal, two grown films, with and without \textit{ex-situ} heating step, have been analysed and compared to determine the differences in their structural, compositional and magnetic properties. The results obtained by the different analysis techniques, in particular M\"ossbauer spectroscopy together with EXAFS and XANES data, suggest that the as-grown film is composed of nanocrystalline maghemite nanoparticles and amorphous strontium oxide. A strontium hexaferrite canonical structure with c-axis orientation in the sample plane was found for the annealed film.

cond-mat.mtrl-sci↗

arXiv2021

Intruders cooperatively interact with a wall into granular matter

When a cylindrical object penetrates granular matter near a vertical boundary, it experiences two effects: its center of mass moves horizontally away from the wall, and it rotates around its symmetry axis. Here we show experimentally that, if two identical intruders instead of one are released side-by-side near the wall, both effects are also detected. However, unexpected phenomena appear due to a cooperative dynamics between the intruders. The net horizontal distance traveled by the common center of mass of the twin intruders is much larger than that traveled by one intruder released at the same initial distance from the wall, and the rotation is also larger. The experimental results are well described by the Discrete Element Method, which reveals a further unexpected phenomenon: when four intruders are released as a column near a wall, they penetrate like a chain that "bends away" from the wall so its lower end is very strongly repelled away from it.

cond-mat.soft↗

arXiv2012

Simultaneous Surface Plasmon Resonance and X-ray Absorption Spectroscopy

We present here an experimental set-up to perform simultaneously measurements of surface plasmon resonance (SPR) and X-ray absorption spectroscopy (XAS) in a synchrotron beamline. The system allows measuring in situ and in real time the effect of X-ray irradiation on the SPR curves to explore the interaction of X-rays with matter. It is also possible to record XAS spectra while exciting SPR in order to detect the changes in the electronic configuration of thin films induced by the excitation of surface plasmons. Combined experiments recording simultaneously SPR and XAS curves while scanning different parameters can be carried out. The relative variations in the SPR and XAS spectra that can be detected with this set-up ranges from 10-3 to 10-5, depending on the particular experiment.

physics.ins-det↗

arXiv2009

Room-temperature ferromagnetism in the mixtures of the TiO2 and Co3O4 powders

We report here the observation of ferromagnetism (FM) at 300 K in mixtures of TiO2 and Co3O4 powders despite the antiferromagnetic and diamagnetic character of both oxides respectively. The ferromagnetic behavior is found in the early stages of reaction and only for TiO2 in anatase structure; no FM is found for identical samples prepared with rutile-TiO2. Optical spectroscopy and X-ray absorption spectra confirm a surface reduction of octahedral Co+3->Co+2 in the mixtures which is in the origin of the observed magnetism

cond-mat.mtrl-sci↗

arXiv2002

A new approach in data reduction: proper handling of random errors and image distortions

Data reduction procedures are aimed to minimize the impact of data acquisition imperfections on the measurement of data properties with a scientific meaning for the astronomer. To achieve this purpose, appropriate arithmetic manipulations with data and calibration frames must be performed. Furthermore, a full understanding of all the possible measurements relies on a solid constraint of their associated errors. We discuss different strategies for obtaining realistic determinations of final random errors. In particular, we highlight the benefits of considering the data reduction process as the full characterization of the raw-data frames, but avoiding, as far as possible, the arithmetic manipulation of that data until the final measure and analysis of the image properties. This philosophy will be used in the pipeline data reduction for ELMER and EMIR.

astro-ph↗

arXiv2001

The New AM Her System RX J0704.2+6203. Northern Twin of BL Hyi

We report here on the identification and study of the optical counterpart of the ROSAT source RX J0704.2+6203. Extensive spectral and photometric observation showed that the object belongs to the class of magnetic Cataclysmic Variables. We determined the orbital period of the system to be 97.27m and estimated the strength of its magnetic field to be on the order of 20 MG. The system was observed in both high and low states, common for its class. Other parameters of the magnetic close binary system were estimated. The spectral and photometric behavior of the object is similar to that of the well studied polar BL Hyi.

astro-ph↗

arXiv1999

Identification of a complete sample of northern ROSAT All-Sky Survey X-ray sources. IV. Statistical analysis

We present the statistical evaluation of a count rate and area limited complete sample of the ROSAT All-Sky Survey (RASS) comprising 674 sources. The RASS sources are located in six study areas outside the galactic plane (|b^II| >= 20 deg) and north of delta = -9 deg. The total sample contains 274 (40.7%) stars, 26 (3.9%) galaxies, 284 (42.1%) AGN, 78 (11.6%) clusters of galaxies and 12 (1.8%) unidentified sources. These percentages vary considerably between the individual study areas due to different mean hydrogen column densities N_H . For the accuracy of the RASS positions, i.e., the distance between optical source and X-ray position, a 90% error circle of about 30 arcsec has been found. Hardness and X-ray-to-optical flux ratios show in part systematic differences between the different object classes. However, since the corresponding parameter spaces overlap significantly for the different classes, an unambiguous identification on the basis of the X-ray data alone is not possible. The majority of the AGN in our sample are found at rather low redshifts with the median value of the whole sample being z_med=0.24. The median values for the individual fields vary between z_med=0.15 and z_med}=0.36. The slope of the log N-log S distributions for our AGN (-1.44 +- 0.09) is in good agreement with the euclidian slope of -1.5. The BL Lacs (with a slope of -0.72+-0.13) exhibit a much flatter distribution.

astro-ph↗

arXiv1998

A New Cataclysmic Variable RX J0757.0+6306: Candidate for the Shortest Period Intermediate Polar

A new cataclysmic variable is identified as the optical counterpart of the faint and hard X-ray source RX J0757.0+6306 discovered during the ROSAT all-sky survey. Strong double-peaked emission lines bear evidence of an accretion disc via an S-wave which varies with a period of 81 +/- 5 min. We identify this period as the orbital period of the binary system. CCD photometry reveals an additional period of 8.52 +/- 0.15 min. which was stable over four nights. We suggest that RX J0757.0+6306 is possibly an intermediate polar, but we cannot exclude the possibility that it is a member of the SU UMa group of dwarf novae.

astro-ph↗

arXiv1997

RX J0719.2+6557: A new eclipsing polar

A new magnetic cataclysmic variable is identified as the counterpart of the X-ray source RX J0719.2+6557. The emission lines show radial velocity variations with a period of 98.2 min. This coincides with the period of deep eclipses (up to 4 mag) in the photometric light curve. The phase of the eclipse relative to the spectroscopic phase, and its structure indicates that the dominant source of emission is located on the stream of accreting matter, which is eclipsed by the secondary companion. The emission lines bear evidence of a weaker component, most probably the contribution from the heated side of the secondary star. These features define this object as a probable polar in a high state. NIR spectroscopy revealed some unusual, strong emission features at 8200 Åand 8660 Åpossibly originating on the heated side of the secondary.

astro-ph↗

arXiv1996

RX J0719.2+6557: A New Eclipsing Polar

A new magnetic, eclipsing cataclysmic variable is identified as the counterpart of the X-ray source RX J0719.2+6557 detected during the ROSAT all-sky survey. The relative phasing of photometric and spectroscopic periods indicates a self-eclipsing system. Doppler tomography points to the heated surface of the secondary as a strong source of emission and of diskless accretion. Near-infrared spectroscopy revealed two unusual strong emission features originating on the heated side of the secondary.

astro-ph↗