Roberto Paniago - Academia.edu (original) (raw)

Papers by Roberto Paniago

Hyperfine Interactions, Mar 31, 2023

Journal of Applied Physics, 2015

Manganites with double perovskite structure are being attractive because of their interesting mag... more Manganites with double perovskite structure are being attractive because of their interesting magnetoelectric and dielectric responses. Particularly, colossal dielectric constant (CDC) behavior has been observed in La 2 CoMnO 6 (LCMO), at radio frequencies and room temperature. In this paper, we employed infrared-reflectivity spectroscopy onto a LCMO ceramic obtained through a modified Pechini's method to determine the phonon contribution to the intrinsic dielectric response of the system and to investigate the CDC origin. The analysis of the main polar modes and of the obtained phonon parameters show that CDC effect of LCMO is of pure extrinsic origin. In addition, we have estimated the dielectric constant and quality factor of the material in microwave region, ' s 16 and Q u × f 124 THz, which shows that LCMO is appropriate for applications into microwave devices and circuitry.

Applied Physics Letters, 2014

ABSTRACT We present an investigation on the magnetic properties of Py/Ru/FeCo/IrMn spin valves gr... more ABSTRACT We present an investigation on the magnetic properties of Py/Ru/FeCo/IrMn spin valves grown by dc magnetron sputtering. The sample fabrication setup has two important features, (i) the five magnetron sputtering sources are placed in a cluster flange 72° from each other, and (ii) each source is tilted with respect to the sample normal. In-plane angular dependence of the ferromagnetic resonance (FMR) was used to obtain the relevant magnetic anisotropies, such as uniaxial and exchange bias fields. The oblique deposition geometry employed has induced non-collinear easy axes of the two ferromagnetic (FM) layers, with high uniaxial field strengths. The symmetry shift of the angular dependence of the FMR resonances of the two FM layers gives us directly the angle between the easy axes of FM1 (Py) and FM2 (FeCo), which turned out to be the angle between two adjacent sputtering sources. The observations of the present study suggest that, by combining oblique deposition and appropriate angles of incidence of the deposition flux, the uniaxial (and unidirectional) axes of individual FM layers can be precisely engineered in spin valve fabrication.

Hyperfine Interactions, 1992

From MOssbauer spectra of 5?Fe with elliptically polarized radiation we fit the coefficients of t... more From MOssbauer spectra of 5?Fe with elliptically polarized radiation we fit the coefficients of the spin (or electric field gradient) texture function expamled in real spherical harmonics up to 1=2. We determine, and show in perspective graphs, the spin texture of the surface of a transformer metal sheet (Fe-Si), of magnetic videotapes (demagnetized and magnetized) aim the electric fiehl gradient texture of a powder of an organometallic eompoumt. We calculate some averages that have an important physical significance.

2D Materials

Naturally occurring van der Waals crystals have brought unprecedented interest to nanomaterial re... more Naturally occurring van der Waals crystals have brought unprecedented interest to nanomaterial researchers in recent years. So far, more than 1800 layered materials (LMs) have been identified but only a few insulating and naturally occurring LMs were deeply investigated. Phyllosilicate minerals, which are a class of natural and abundant LMs, have been recently considered as a low-cost source of insulating nanomaterials. Within this family an almost barely explored material emerges: phlogopite (KMg3(AlSi3)O10(OH)2). Here we carry out a high throughput characterization of this LM by employing several experimental techniques, corroborating the major findings with first-principles calculations. We show that monolayers (1L) and few-layers of this material are air and temperature stable, as well as easily obtained by the standard mechanical exfoliation technique, have an atomically flat surface, and lower bandgap than its bulk counterpart, an unusual trend in LMs. We also systematically s...

In agriculture has been employed indiscriminate use of chemical insecticides in order to combat p... more In agriculture has been employed indiscriminate use of chemical insecticides in order to combat pests causing the emergence of resistant biotypes leading to the use of increasingly higher doses without obtaining a satisfactory result. Natural products from plants may be a viable alternative to pest control, minimizing impacts to the environment. In this sense the use of plant extracts containing insecticidal activity may be appropriate to control harmful insects. In this work we present the development of nanocomposite magnetic nanoparticles of iron oxides, magnetite type (Fe3O4) functionalized with the extract of Azadirachta indica to be used as an alternative insecticide Spodoptera frugiperda is a pest of major importance in maize by reducing up to 34% plantations productivity. The prepared nanobiotechnological insecticide can also be applied to other type of pest.

Revista ECIPeru, 2018

Progresos en la preparación de nanopartículas magnéticas multifuncionales para aplicación en la m... more Progresos en la preparación de nanopartículas magnéticas multifuncionales para aplicación en la medicina Progress in the preparation of magnetic nanoparticles for applications in medicine Jorge Luis López Aguilar1, José Higino Dias Filho2, Roberto Paniago3, Hans D.- Pfannes3, Karla Balzuweit3 1Universidad Federal de Acre, Ciências Biológicas e da Natureza, Rio Branco, Brasil 2Universidad Estadual de Montes Claros, Departamento de Ciências Exatas, Montes Claros, MG, Brasil 3Universidad Federal de Minas Gerais, Departamento de Física, Belo Horizonte, MG, Brasil DOI: https://doi.org/10.33017/RevECIPeru2013.0014/ Resumen En este trabajo hacemos una revisión de tres rutas de síntesis de nanopartículas de magnetita (Fe3O4) funcionalizadas que pueden utilizarse para transportar fármacos. Este tipo de partículas no tóxicas, son sin duda, uno de los grandes responsables por el avance en el tratamiento médico contra tumores, entrega dirigida de fármacos, inmovilización de enzimas, purificaci...

Journal of Nanoscience and Nanotechnology, 2009

ABSTRACT

Nanomaterials

In this work, flower-like molybdenum disulfide (MoS2) microspheres were produced with polyethylen... more In this work, flower-like molybdenum disulfide (MoS2) microspheres were produced with polyethylene glycol (PEG) to form MoS2-PEG. Likewise, gold nanoparticles (AuNPs) were added to form MoS2-PEG/Au to investigate its potential application as a theranostic nanomaterial. These nanomaterials were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoelectron X-ray spectroscopy (XPS), Fourier-transformed infrared spectroscopy (FTIR), cyclic voltammetry and impedance spectroscopy. The produced hierarchical MoS2-PEG/Au microstructures showed an average diameter of 400 nm containing distributed gold nanoparticles, with great cellular viability on tumoral and non-tumoral cells. This aspect makes them with multifunctional characteristics with potential application for cancer diagnosis and therapy. Through the complete morphological and physicochemical characterization, it was possible to observe that both MoS2-PEG and...

SSRN Electronic Journal, 2021

Ceramics International, 2018

Gd 2 CoMnO 6 and Y 2 CoMnO 6 double perovskite ceramics were obtained from the polymeric precurso... more Gd 2 CoMnO 6 and Y 2 CoMnO 6 double perovskite ceramics were obtained from the polymeric precursors method and investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman and Fourier Transform Infrared (FTIR) spectroscopies. Our results show that these samples present similar structural and vibrational characteristics that are fully compatible with a monoclinic structure belonging to the P2 1 /n space group, with ordered Co 2+ and Mn 4+ cations. Infrared-reflectivity spectroscopy was employed to investigate the polar phonon features and to determine the intrinsic dielectric response of the materials. In particular, the extrapolated dielectric constants at the lower frequency infrared limit showed to be independent on the particle size, and were determined as and 16.0, for Gd 2 CoMnO 6 and Y 2 CoMnO 6 , respectively. Otherwise, it is shown that for smaller RE radius the FTIR bands become more evidenced, due to a higher octahedral rotation and lower CoO -Mn angle into the distorted monoclinic structure.

Journal of Water Process Engineering, 2015

This paper describes the preparation, characterization and photocatalytic properties of the novel... more This paper describes the preparation, characterization and photocatalytic properties of the novel floating composite, consisting of TiO 2 supported on autoclaved cellular concrete (ACC). The material was characterized using photoelectron spectroscopy excited by X-rays, scanning electron microscopy (SEM), as well as electronic and atomic absorption spectroscopy. BET (Brunauer, Emmett, Teller) measurements determined the composite surface area. The photocatalytic activity of the novel floating material, upon exposure to UV radiation, was tested for the degradation of indigo carmine, chosen as a model substrate. The performance of three distinct systems, TiO 2 /ACC/UV, TiO 2-P25/UV and UV (photolysis), in the oxidation of indigo carmine was studied utilizing liquid chromatography coupled to mass spectrometry (HPLC-MS). The results indicated that whereas the TiO 2-P25/UV and UV systems displayed degradation rates of roughly 60%, TiO 2 /ACC/UV is by far the most efficient system with removal rates of about 100%, after 350 min of exposure. The novel photocatalytic system also yielded higher mineralization rates in comparison to photolysis. We have also studied the photodegradation of diclofenac (a pharmaceutical compound) and atrazine (a pesticide), induced by the same catalyst. Finally, the toxicities of the reaction aliquots were determined against brine shrimp (Artemia salina). Therefore, the novel TiO 2 /ACC floating composite presents promising potential to act as a photocatalyst to degrade a number of organic contaminants in water.

Polymer Testing, 2008

Conducting polymer blends whose undiluted components have different properties are promising mate... more Conducting polymer blends whose undiluted components have different properties are promising materials for several technological applications such as electromagnetic shielding, electrostatic charge dissipation, optoelectronic displays, chemical sensors, biosensors and electromechanical sensors. The aim of this study was to obtain and evaluate the electrical conductivity and electromechanical properties of a polystyreneblock-poly(ethylene-ran-butylene)-block-polystyrene copolymer (SEBS)/polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA) blends. Electrically conductive elastomeric blends based on SEBS/PAni.DBSA were prepared through a solution casting method, at room temperature, after dissolving both components in toluene as a common solvent. SEBS/PAni.DBSA blends were also prepared through polymerization of aniline in the presence of SEBS solution, using a one-step in situ emulsion polymerization method. The protonation degree of the PAni.DBSA used in this study was determined from X-ray photoelectron spectroscopy (XPS) analysis by calculating the amount of different neutral and positive nitrogen species of the polyaniline chain from the properly curve-fitted N-1s core-level spectrum. The PAni.DBSA used to prepare solution casting blends had a 46% protonation degree, with almost all imine groups protonated and only a small amount of residual DBSA, as expected for an emeraldine salt. This protonation degree is responsible for the high conductivity (2.4 S cm À1) and good solubility of this conducting polymer in toluene. The protonation degree of PAni.DBSA in the blends analyzed was higher than that of undiluted PAni.DBSA, due to an additional protonation during the casting or in situ processes. The insulator-conductor transition was not as sharp as those found in carbon black conducting systems and the percolation threshold was lower than 20 wt.% of PAni. DBSA. Above 20 wt.% PAni.DBSA content, the emulsion-polymerized systems had higher volume conductivity values than the corresponding solution casting blends. The mechanical properties such as tensile strength, elastic modulus and elongation at break of SEBS/PAni.DBSA blends were dependent on the blend preparation method. Blends were also characterized by electromechanical properties and optical microscopy.

Journal of Physics: Condensed Matter, 2010

Journal of Magnetism and Magnetic Materials, 2008

We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter o... more We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300K under zero external DC field for frequencies ranging from f=10 to 10,000Hz. A prominent peak appears in both χ′ and χ″ as a function of

RSC Advances, 2014

All-inorganic layer-by-layer TiO2–Nb2O5 films were applied as underlayers in DSCs, leading to an ... more All-inorganic layer-by-layer TiO2–Nb2O5 films were applied as underlayers in DSCs, leading to an expressive improvement on the conversion efficiency.

International Journal of Photoenergy, 2012

The influence of pH during hydrolysis of titanium(IV) isopropoxide on the morphological and elect... more The influence of pH during hydrolysis of titanium(IV) isopropoxide on the morphological and electronic properties of TiO2nanoparticles prepared by the sol-gel method is investigated and correlated to the photoelectrochemical parameters of dye-sensitized solar cells (DSCs) based on TiO2films. Nanoparticles prepared under acid pH exhibit smaller particle size and higher surface area, which result in higher dye loadings and better short-circuit current densities than DSCs based on alkaline TiO2-processed films. On the other hand, the product of charge collection and separation quantum yields in films with TiO2obtained by alkaline hydrolysis is c.a. 27% higher than for the acid TiO2films. The combination of acid and alkaline TiO2nanoparticles as mesoporous layer in DSCs results in a synergic effect with overall efficiencies up to 6.3%, which is better than the results found for devices employing one of the nanoparticles separately. These distinct nanoparticles can be also combined by us...

Materials Science and Engineering: C