A5069986398- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Rare-earth and actinide compounds
- Crystallization and Solubility Studies
- Crystal Structures and Properties
- X-ray Diffraction in Crystallography
- Magnetic Properties of Alloys
- Iron-based superconductors research
- High-pressure geophysics and materials
- Metal complexes synthesis and properties
- Physics of Superconductivity and Magnetism
- Boron and Carbon Nanomaterials Research
- Iron oxide chemistry and applications
- Magnetic properties of thin films
- Superconductivity in MgB2 and Alloys
- Multiferroics and related materials
- Nanomaterials for catalytic reactions
- Geological and Geochemical Analysis
- Metal-Catalyzed Oxygenation Mechanisms
- ZnO doping and properties
- Nuclear materials and radiation effects
- Thermal Expansion and Ionic Conductivity
- Electronic and Structural Properties of Oxides
- Inorganic Chemistry and Materials
- Catalytic Processes in Materials Science
Universidade Federal Fluminense
2015-2024
Universidade Nova de Lisboa
2024
Centro Brasileiro de Pesquisas Físicas
2000-2011
University of Cambridge
2006-2011
Universidade do Estado do Rio de Janeiro
2009
Instituto de Ciencia de Materiales de Madrid
2002-2005
University of Houston
2005
Consejo Superior de Investigaciones Científicas
2002-2004
National Council for Scientific and Technological Development
1997-2001
Iowa State University
2000
Antisite disordering in ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ double perovskites (containing Mo atoms at Fe positions, and vice versa) has recently been shown to have a dramatic influence their magnetic magnetotransport properties. In the present paper, two polycrystalline samples showing different degrees of antisite disorder (a nominally ``ordered'' sample with \ensuremath{\sim}70% cationic ordering ``disordered'' \ensuremath{\sim}18% ordering) examined by measurements neutron powder...
We present a study of the transport and magnetic properties series $R\mathrm{NiBC}$ compounds $(R=\mathrm{Er},$ Ho, Dy, Tb, Gd). All materials investigated have long range order at sufficiently low temperatures. Magnetoresistance measurements are presented for large temperatures (T) fields (H). show that below critical temperature, temperature dependence resistivity is determined by electron scattering due to elementary excitations (spin waves) ordered phase values gap in magnon spectra were...
There are two known ludwigites containing a single transition metal element, ${\text{Fe}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ and ${\text{Co}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$. The structure of these materials has low-dimensional units in the form three-legged ladders (3LL) that confer to each them unique magnetic electronic properties. presents staggered charge density wave (CDW) near room temperature transitions. It remained mystery why other compound...
Iron oxide nanoparticles (FeONPs) prepared with plant extracts have been emerging as green and sustainable materials. FeONPs are usually amorphous due to the chelation of tea polyphenols (TPs) iron, real nature iron compounds is not completely understood. The main goal this study was investigate behavior synthesized from an Fe3+ salt Cammelia sinensis (black tea) extract upon thermal treatment, in order remove TPs enable formation crystalline materials suitable for a thorough...
We present an extensive study of the oxyborate material ${\text{Co}}_{5}\text{Ti}{({\text{O}}_{2}{\text{BO}}_{3})}_{2}$ using x-ray, magnetic, and thermodynamic measurements. This belongs to a family oxyborates known as ludwigites which presents low-dimensional subunits in form three leg ladders its structure. Differently from previously investigated does not show long-range magnetic order although it goes into spin-glass state at low temperatures. The different techniques employed this...
The ludwigite ${\text{Co}}_{5}\text{Sn}({\mathrm{O}}_{2}{\text{BO}}_{3}{)}_{2}$ was studied using x-ray diffraction, M\"ossbauer spectroscopy, and magnetic thermodynamic measurements. This material belongs to a family of oxyborates which presents low-dimensional subunits in the form three-leg ladders its structure. confer these materials strong anisotropy their exchange interactions that provide ludwigites several interesting properties, from partial ordering spin-glass states. Despite being...
Electron doping effects on Sr2FeMoO6 have been investigated in the title series by X-ray diffraction (XRD), neutron powder (NPD) and magnetic measurements polycrystalline samples. XRD patterns show that anti-site defects concentration increases with x, giving rise to highly disordered samples at B positions, for highest levels. The study of evolution structural parameters valence state Fe Mo cations doping, followed NPD, sheds some light observed changes properties, particular ferromagnetic...
We have succeeded in the preparation of a broad set epitaxial Sr2FeMoO6 thin films by pulsed laser deposition. studied effect various deposition conditions, on both substrate-induced strain and antisite disorder (ASD), which translate into variety magnetic transport properties films. find that saturation magnetization magnetoresistance are dominated degree cationic order, effects clearly evidenced lower TC. characterize ASD induced magnetoresistance, arises from moderate concentration...
The homometallic $\mathrm{Fe}$ ludwigite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{2}{\mathrm{BO}}_{3}$, is an oxyborate with a chain structure of oxygen octahedra occupied by ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ four different crystallographic sites. We report $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopic studies on the magnetic spin arrangements charge ordering in between $4$ $450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. From temperature dependence isomer shifts quadrupole interactions,...
The mixed-valent homometallic ludwigite $({\mathrm{Co}}_{2}^{2+}{\mathrm{Co}}^{3+}){\mathrm{O}}_{2}{\mathrm{BO}}_{3}$ is investigated above the ferrimagnetic ordering temperature ${T}_{C}=43\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ through structural, thermal, magnetic, electric, and spectroscopic probes. X-ray absorption at Co ${L}_{2,3}$ edges consistent with coexistence of ${\mathrm{Co}}^{2+}$ ${\mathrm{Co}}^{3+}$ ions, as expected by sample stoichiometry. Magnetic susceptibility shows a...
${}^{57}$Fe M\"ossbauer spectra of REN${\mathrm{i}}_{2}$${\mathrm{B}}_{2}$C ( $\mathrm{RE}=\mathrm{Tb}$, Dy, Ho, Er) doped with 1 at. % show a magnetic hyperfine field ${B}_{\mathrm{hf}}$ at the nucleus in TbN${\mathrm{i}}_{2}$${\mathrm{B}}_{2}$C for $T<{T}_{N}\ensuremath{\sim}15\mathrm{K}$ and HoN${\mathrm{i}}_{2}$${\mathrm{B}}_{2}$C $5.5>T>4.2\phantom{\rule{0ex}{0ex}}\mathrm{K}$. $\mathrm{No}$ is observed superconducting DyN${\mathrm{i}}_{2}$${\mathrm{B}}_{2}$C...
57Fe Mössbauer spectroscopy has been used to investigate the structural and magnetic phase transitions of CaFe2As2 (TN = 173 K) single crystals. For this compound we found that VZZ is positive parallel c-axis tetragonal structure. a hyperfine field Bhf was observed at nucleus below TN ∼ K. Analysis temperature dependence data using Bean–Rodbell model shows Fe spins undergo first-order transition A collinear antiferromagnetic structure established with spin lying in (a, b) plane. Below...
The stoichiometric perovskites RMnO3 (R = rare earth) experience Jahn–Teller (JT) transitions as a function of temperature and R size similar to that recently described for LaMnO3. We have investigated the JT transition Pr by ATD techniques neutron powder diffraction. This takes place at approximately 1050 K, it is characterized strong reduction MnO6 octahedra sudden changes in unit cell parameters Mn–O bond distances. For T < TJT, PrMnO3 perovskite exhibits so-called O′ orthorhombic...
Static magnetic order of quasi two-dimensional FeAs compounds Sr4A2O6-xFe2As2, with A = Sc and V, has been detected by 57Fe Moessbauer muon spin relaxation ({\mu}SR) spectroscopies. The non-superconducting stoichiometric (x 0) system exhibits a static internal/hyperfine field both at the {\mu}+ sites, indicating antiferromagnetic Fe moments below TN 35 K ~ 0.1 Bohr magneton per T 2 K. superconducting oxygen deficient 0.4) V internal only site 40 K, co-existing superconductivity without...
We have used electron spin resonance to study an epitaxial thin-film sample of the manganite La${}_{0.6}$Ca${}_{0.4}$MnO${}_{3}$ in which ferromagnetic and paramagnetic phases were previously shown coexist [Phys. Rev. B 78, 054409 (2008)]. Resonant absorbtions arise on either side reveal that phase is itself separated into regions with Curie temperatures \ensuremath{\sim} 190 250 K. This extra complexity attributed coexistence strained relaxed regions, as verified by x-ray diffraction.
This paper presents an extensive study of the structural, magnetic, and thermodynamic properties heterometallic ludwigite ${\mathrm{Co}}_{4.76}{\mathrm{Al}}_{1.24}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$. material orders ferrimagnetically at 57 K. Despite fact that, in ${\mathrm{Co}}_{4.76}{\mathrm{Al}}_{1.24}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$, one quarter Co ions parent compound ${\mathrm{Co}}_{3}{\mathrm{O}}_{2}{\mathrm{BO}}_{3}$ is replaced by nonmagnetic ${\mathrm{Al}}^{3+}$...
In this work, we investigated the effects of postdeposition heat treatment on structural and magnetic properties CoFe2O4 nanoparticles produced by pulsed laser deposition. Structural analysis X-ray diffraction, transmission electron microscopy (TEM) Mössbauer spectroscopy indicate formation a single phase cobalt ferrite with size ranging from 4.3 to 33.3 nm depending annealing temperature. The samples were in wide temperature range (50–400 K). Noticeable cubic magnetocrystalline anisotropy...
Charge ordering is prone to occur in crystalline materials with mixed-valence ions. It presumably accompanied by a structural phase transition, possible exceptions compounds that already present more than one inequivalent site for the ions charge-disordered phase. In this work, we investigate representative case of homometallic Co ludwigite ${\mathrm{Co}}_{2}^{2+}{\mathrm{Co}}^{3+}{\mathrm{O}}_{2}{\mathrm{BO}}_{3}$ ($Pbam$ space group) four distinct crystallographic sites [$M1$--$M4$]...
Perfluorooctanoic acid (PFOA) has been widely studied due to its environmental persistence and bioaccumulation potential, raising concerns about effects on aquatic life. This research evaluates the impact of PFOA antioxidant defenses stress response systems mussel Mytilus galloprovincialis. Mussels were exposed three concentrations (1, 10, 100 µg·L−1) over 28 days. Several biomarkers, including glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), lipid peroxidation...
In thin-film ${\text{La}}_{0.6}{\text{Ca}}_{0.4}{\text{MnO}}_{3}$, conducting-tip and magnetic force microscopy reveal a pattern of nanoscale phase separation that is reproducible across cooling runs. This represents the intersection buried three-dimensional filamentary ferromagnetic metallic pathways with sample surface. As an interlayer in current-perpendicular-to-the-plane trilayer devices, this phase-separated material magnetically decouples...