Luiz Nagamine - Academia.edu (original) (raw)

Papers by Luiz Nagamine

Materials Advances

When Fe-ions enter into the ZnO NPs, their oxidation state can be tuned and the excitonic peak en... more When Fe-ions enter into the ZnO NPs, their oxidation state can be tuned and the excitonic peak enlarges, indicating that the ZnO lattice becomes more disordered. The AFM interactions found in paramagnetic NPs become stronger as Fe content increases.

Physical Chemistry Chemical Physics, 2020

In this work, we present a coupled experimental and theoretical first-principles investigation on... more In this work, we present a coupled experimental and theoretical first-principles investigation on one of the more promising oxide-diluted magnetic semiconductors, the Sn1−xCoxO2 nanoparticle system, in order to see the effect of cobalt doping on the physical and chemical properties.

Hyperfine Interactions, 1999

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012

ABSTRACT In the present work, we report experimental results of He stopping power into Al2O3 film... more ABSTRACT In the present work, we report experimental results of He stopping power into Al2O3 films by using both transmission and Rutherford backscattering techniques. We have performed measurements along a wide energy range, from 60 to 3000 keV, covering the maximum stopping range. The results of this work are compared with previously published data, showing a good agreement for the high-energy range, but evidencing discrepancies in the low-energy region. The existing theories follow the same tendency: good theoretical–experimental agreement for higher energies, but they failed to reproduce previous and present results in the low energy regime. On the other hand it is interesting to note that the semi-empirical SRIM code reproduces quite well the present data.

Thin Solid Films, 2008

The aim of this work is to investigate the effects of 593 MeV Au irradiation using two different ... more The aim of this work is to investigate the effects of 593 MeV Au irradiation using two different projectile charges, namely Au 30+ and Au 46.3+ on the structural, transport and magnetization properties of Co/NiFe/Co/Cu multilayers. X-Ray diffraction and extended x-ray absorption fine structures measurements show no significant structural change for as deposited and irradiated multilayers. On the other hand, the magnetoresistance amplitude decreases with the ion fluence but it is insensitive to the projectile charge state. The correlation between changes in the magnetoresistance and remanent magnetization suggests that the main effect responsible for the decrease of the magnetoresistance is the creation of ferromagnetic pinholes. These results are discussed on basis of the electronic thermal spike model and nuclear cascades theory and show similarities to the effects observed at low-energy ion-beam irradiation.

Journal of Magnetism and Magnetic Materials, 2004

The exchange bias effect is measured for a Co/NiO bilayer before and after it has been cooled dow... more The exchange bias effect is measured for a Co/NiO bilayer before and after it has been cooled down from 580 K in 1.5 kOe magnetic field applied at 45 to the initial exchange-bias direction. The angular variation of the hysteresis loop shift for the treated sample showed three distinct minima and maxima, in contrast to that of the as-made sample, which is characteristic for a system with aligned ferromagnetic and antiferromagnetic easy axes. This behavior is qualitatively well explained in the framework of the domain-wall formation model applied for the off-aligned case.

Journal of Magnetism and Magnetic Materials, 1996

The spin reorientation transition in DyFel0Si 2 has been investigated. Susceptibility versus temp... more The spin reorientation transition in DyFel0Si 2 has been investigated. Susceptibility versus temperature data show a peak at 225 K, while MiSssbauer hyperfine parameters show the axial-conical SR temperature~to be TSR-245 K. This temperature corresponds to the maximum negative slope in the X versus T curve. Spins rotate smoothly, down to T-: 200 K, and no sign ofa conical-planar reorientation was found at lower temperatures.

Journal of Applied Physics, 1994

ABSTRACT

$Research paper thumbnail of Magnetic Properties of <formula formulatype="inline"><tex Notation="TeX">$\gamma-{\rm Fe}_{2}{\rm O}_{3}$</tex> </formula> Nanoparticles at the Verge of Nucleation Process$

IEEE Transactions on Magnetics, 2013

ABSTRACT A low-energy new method based in a one-step synthesis at room temperature produces very ... more ABSTRACT A low-energy new method based in a one-step synthesis at room temperature produces very small maghemite nanoparticles. The fast neutralization reaction (co-precipitation) of a ferric solution (FeCl 3 aqueous) in a basic medium (NH 4 OH concentrated) produces an intermediate phase, presumably two-line ferrihydrite, that in oxidizing conditions is transformed to maghemite nanoparticles. That "primordial soup" is characterized by small atoms arrangements, that are the base for maghemite tiny crystals. The final product of the reaction was characterized by X-Ray Diffraction, High-Resolution Transmission Electron Microscopy, X-ray Absorption Fine Structure, Mössbauer spectroscopy, and magnetometry.

Hyperfine Interactions, 2011

In this work, we report on the study of SnO 2 nanoparticles prepared by a polymer precursor metho... more In this work, we report on the study of SnO 2 nanoparticles prepared by a polymer precursor method. X-ray diffraction (XRD) data analysis evidenced the formation of only the tetragonal rutile-type phase for the as-grown and thermally annealed samples. A mean grain size of about 11 nm for the as-prepared sample has been determined. This mean size increases after the thermal annealing and with the annealing temperature. The room temperature Mössbauer spectra (MS) were well fitted using a quadrupole splitting (QS) distribution. The isomer shift (IS) tends to increase when the grain size decreases. That increase has been associated to the extra s-electron density generated by the oxygen vacancies.

Capítulo l-Introdução Capitulo 1-Introdução 1.1-Ímãs permanentes à base de intermetálicos terra r... more Capítulo l-Introdução Capitulo 1-Introdução 1.1-Ímãs permanentes à base de intermetálicos terra rara-metal de transição (R-M). A necessidade de novos materiais para a confecçãó de ímãs pennanentes, em grande parte gerada peja miníaturização de díspositivos, tem estimulado uma intensa

International Journal of Molecular Sciences, 2021

In nanomedicine, hybrid nanomaterials stand out for providing new insights in both the diagnosis ... more In nanomedicine, hybrid nanomaterials stand out for providing new insights in both the diagnosis and treatment of several diseases. Once administered, engineered nanoparticles (NPs) interact with biological molecules, and the nature of this interaction might directly interfere with the biological fate and action of the NPs. In this work, we synthesized a hybrid magnetic nanostructure, with antibacterial and antitumoral potential applications, composed of a magnetite core covered by silver NPs, and coated with a modified chitosan polymer. As magnetite NPs readily oxidize to maghemite, we investigated the structural properties of the NPs after addition of the two successive layers using Mössbauer spectroscopy. Then, the structural characteristics of the NPs were correlated to their interaction with albumin, the major blood protein, to evidence the consequences of its binding on NP properties and protein retention. Thermodynamic parameters of the NPs–albumin interaction were determined...

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021

Abstract Superparamagnetic iron oxide nanoparticles (SPIONs) are interesting for biomedical appli... more Abstract Superparamagnetic iron oxide nanoparticles (SPIONs) are interesting for biomedical applications in cancer treatment via magneto-hyperthermia. Its potential application contrasts with the challenges in producing systems with chemical and morphological uniformity and colloidal stability using simple, low-cost, and sustainable routes. Aqueous syntheses usually fail to control morphology and composition because SPIONs formation mechanisms are not fully understood. Here, we propose an aqueous route to synthesize SPIONs based on the controlled and stoichiometric reduction in situ of Fe3+ to Fe2+ ions in the presence of sulfite ions, followed by aging at 90 ∘C in an alkaline medium for 18h. SPIONs with high water-stable and controlled characteristics in a sustainable, inexpensive, and scalable procedure were obtained. The nucleation, growth, and hydrolysis rates were adjusted by the excess of OH− ions, initial temperature, and iron precursor nature. The results are discussed concerning concepts of the classical and nonclassical nucleation theories, indicating an optimum pH of 9.5-10.5 for SPIONs formation. The SPIONs present an average size of 11 nn, narrow size distribution, and magnetite phase with about 34 mol% of maghemite due to structural defects. Nanoparticles are superparamagnetic, have a hydrodynamic diameter of 130 nm with a surface potential of ~ -40 mV (pH ≥ 7), and suitable magneto-hyperthermic properties fro cancer treatment. Specific Absorption Rate values were evaluated concerning the SPIONs physical-chemical properties, indicating a strong dependence on the average crystallite size and the magnetization at 250 Oe. Cell viability tests showed that SPIONs did not provide any significant change in cellular growth at used concentrations.

dedicada e pela amizade. .4o Pr'of. Dr'. Alderr E-Ray pel:rs; :rmostr'es f or.necides e discussõe... more dedicada e pela amizade. .4o Pr'of. Dr'. Alderr E-Ray pel:rs; :rmostr'es f or.necides e discussões dcrs r'çsult ados. À Pr-of'. Dn. Õa¡'nrer¡ C. M. Par'titi pela ajucla ir¡icial e dÍo-cusslões. Ao Pr'of. Dr.. Frank P. Missel pela bibliografia cedida. Ac¡ Pr'of'. Dr.. Ney F. OliveÍr'a Jr. pela per.missão do r¡scr da impressorå e do plciter. .Á ValqrrÍr'ia Villas-Boas pt=Ii:s discrrss?ies na par-te de r'¿ric, X. Ao Er'orrides Almeida pelo apoio Lécr¡ico rrc¡ labor'atór'io. Âo Douglas A. P. Brrlla peilas nredid¿rs de, r'aio X. Ao pessoal da sala 1O9 pela anrizade e cclmpänheir.ismo. Ao pessoal da ofic;irra mecårrica. Ao CNPQ pelo apoio fir¡ar¡ceir.o. Ar:s rn{=us p:ris pelo apoic¡ e incerrt,ivo.

The Journal of Physical Chemistry C, 2015

We present a study where the energy loss function of Ta 2 O 5 , initially derived in the optical ... more We present a study where the energy loss function of Ta 2 O 5 , initially derived in the optical limit for a limited region of excitation energies from reflection electron energy loss spectroscopy (REELS) measurements, was improved and extended to the whole momentum and energy excitation region through a suitable theoretical analysis using the Mermin dielectric function and requiring the fulfillment of physically motivated restrictions, such as the f-and KK-sum rules. The material stopping cross section (SCS) and energy-loss straggling measured for 300−2000 keV proton and 200− 6000 keV helium ion beams by means of Rutherford backscattering spectrometry (RBS) were compared to the same quantities calculated in the dielectric framework, showing an excellent agreement, which is used to judge the reliability of the Ta 2 O 5 energy loss function. Based on this assessment, we have also predicted the inelastic mean free path and the SCS of energetic electrons in Ta 2 O 5. We present a joint experimental-theoretical study where the excitation spectrum of Ta 2 O 5 measured by reflection electron energy loss spectroscopy (REELS), which only covers a small region (optical, i.e., zero momentum transfer, and valence electron excitations), is improved and extended to the whole excitation region through a suitable theoretical analysis that requires the fulfillment of physically motivated sum rules 15 and 49 includes the contribution of intermediate and inner shell 50 excitations. The resulting ELF is used as input for the dielectric 51 formalism to evaluate the energy loss magnitudes characterizing 52 the passage of swift ions through matter. These calculations are 53 compared with the measured stopping cross section and 54 energy-loss straggling of Ta 2 O 5 films for proton and helium ion 55 beams by means of Rutherford backscattering spectrometry. 56 The excellent agreement between the experimental and 57 theoretical results is used as an assessment of the derived 58 energy loss function for Ta 2 O 5. 59 Due to its high dielectric constant, chemical and thermal 60 stability, as well as wear resistance, tantalum oxide (Ta 2 O 5) is a 61 promising material for solar energy conversion systems, 62 CMOS-based technology and resistive random access memo-63 ries. 16−19 Therefore, it is important to have a proper knowledge 64 of the electronic excitation spectrum of this material, which is 65 provided in this work as previously described. 66 This paper is organized as follows. In section II, the energy 67 loss function of Ta 2 O 5 in the optical limit (zero momentum 68 transfer, ℏk = 0) is derived from REELS measurements. This 69 energy loss function is extended in section III to the whole