São Cristóvão, Brazil
São Cristóvão, Brazil

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de Souza M.V.,Nucleo de Pos Graduacao em Fisica | da Silva J.A.,Nucleo de Pos Graduacao em Fisica | Silva L.S.,Nucleo de Pos Graduacao em Fisica | Silva L.S.,Federal University of Santa Maria
Journal of Magnetism and Magnetic Materials | Year: 2017

We report the magneto-thermal and resistive properties of rare-earth dialuminide NdAl2, including spin reorientation transition. To this purpose, we used a theoretical model that considers the interactions of exchange and Zeeman, besides the anisotropy due to the electrical crystal field. The theoretical results obtained were compared to experimental data of the NdAl2 in single crystal and bulk forms. Explicitly, we have calculated the anisotropic variation of magnetic entropy with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111] of NdAl2 single crystal, where a signature of the spin reorientation is observed in the [110] and [111] directions. Moreover, of magnetoresistivity we consider the applied magnetic field along the crystallographic directions [100] and [110]. In turn, for the polycrystalline form, the good agreement between theory and experiment confirms the presence of spin reorientation, which was predicted theoretically in magnetization curves. © 2016 Elsevier B.V.


Fabian F.A.,Nucleo de Pos Graduacao em Fisica | Moura K.O.,University of Campinas | Barbosa C.C.S.,Nucleo de Pos Graduacao em Fisica | Peixoto E.B.,Nucleo de Pos Graduacao em Fisica | And 4 more authors.
Journal of Alloys and Compounds | Year: 2017

We report on thermogravimetric, structural and magnetization measurements in the YCrO3+γ compound obtained by the co-precipitation method. The thermogravimentric analyses show that the weight losses which occur at three distinct steps are associated with water evaporation, formation of zircon-type YCrO4 compound and finally a phase transition from the tetragonal YCrO4 to the orthorhombic YCrO3. The X-ray diffraction measurements allied with the Rietveld refinement confirm such trend, that is, the observed X-ray patterns are consistent with a gradual growth of zircon-type YCrO4 with tetragonal structure and space group I41/amd for annealing temperatures up to 600 °C followed by the phase transition to the orthorhombic YCrO3 phase with space group Pbnm for annealing temperatures above 625 °C. The X-ray absorption near edge structure (XANES) spectra carried out in the Cr K-edge reveal that the oxidation states of Cr ions depend on the synthesis temperature. The T-dependencies of magnetic susceptibility point out a ferromagnetic-antiferromagnetic transition as function synthesis temperature. The Curie and Neel temperatures are in agreement with that reported in literature for the YCrO4 and YCrO3 compounds, respectively. Besides, the MvsH curves measured at 2 and 50 K are consistent with the observed magnetic states to each sample. © 2017 Elsevier B.V.


Sarveena,H P University | Vargas J.M.,Bariloche Atomic Center | Shukla D.K.,UGC-DAE Consortium for Scientific Research | Meneses C.T.,Nucleo de Pos Graduacao em Fisica | And 4 more authors.
Physical Chemistry Chemical Physics | Year: 2016

The present work describes the synthesis of iron oxide nanoparticles by thermal decomposition of Fe-precursors in argon and vacuum environments with control over particle size distribution, phase composition and the resulting magnetic properties. The Rietveld refinement analysis of X-ray diffraction data revealed the crystallinity as well the single-phase of γ-Fe2O3 nanoparticles prepared under vacuum, whereas the argon environment leads to the formation of multi-phase composition of γ-Fe2O3/Fe3O4 (90%) and wustite (10%). Synchrotron X-ray absorption near edge structure (XANES) indicates that the predominant phase in both samples is γ-Fe2O3, which is subsequently verified from the Mössbauer spectra. DC magnetic measurements indicate behavior typical of a superparamagnetic system validated by Mössbauer analysis. However, further investigation of ac susceptibility by typical Néel-Arrhenius and Vogel Fulcher magnetic models suggests an influence of interparticle interactions on the overall magnetic behavior of the system. © the Owner Societies 2016.


PubMed | National University of La Plata, H P University, UGC-DAE Consortium for Scientific Research, Federal University of Maranhão and 2 more.
Type: Journal Article | Journal: Physical chemistry chemical physics : PCCP | Year: 2016

The present work describes the synthesis of iron oxide nanoparticles by thermal decomposition of Fe-precursors in argon and vacuum environments with control over particle size distribution, phase composition and the resulting magnetic properties. The Rietveld refinement analysis of X-ray diffraction data revealed the crystallinity as well the single-phase of -Fe2O3 nanoparticles prepared under vacuum, whereas the argon environment leads to the formation of multi-phase composition of -Fe2O3/Fe3O4 (90%) and wustite (10%). Synchrotron X-ray absorption near edge structure (XANES) indicates that the predominant phase in both samples is -Fe2O3, which is subsequently verified from the Mssbauer spectra. DC magnetic measurements indicate behavior typical of a superparamagnetic system validated by Mssbauer analysis. However, further investigation of ac susceptibility by typical Nel-Arrhenius and Vogel Fulcher magnetic models suggests an influence of interparticle interactions on the overall magnetic behavior of the system.


Carvalho M.H.,Nucleo de Pos Graduacao em Fisica | Lima R.J.S.,Federal University of Campina Grande | Meneses C.T.,Nucleo de Pos Graduacao em Fisica | Folly W.S.D.,Federal University of Sergipe | And 3 more authors.
Journal of Applied Physics | Year: 2016

We present a systematic study of the coercive field of CoFe2O4-SiO2 nanocomposites. The samples were prepared via the sol-gel method by using the Tetraethyl Orthosilicate as starting reagent. Results of X-ray diffraction, transmission electron microscopy, and X-ray fluorescence confirm the dispersion of the magnetic nanoparticles inside the silica matrix. In addition, the shift in the maximum of Zero-Field-Cooled curves observed by varying the weight ratio of CoFe2O4 nanoparticles to the precursor of silica is consistent with the increasing of average interparticle distances. Because our samples present a particle size distribution, we have used a generalized model which takes account such parameter to fit the experimental data of coercive field extracted from the magnetization curves as a function of applied field. Unlike most of the coercive field results reported in the literature for this material, the use of this model provided a successful description of the temperature dependence of the coercive field of CoFe2O4 nanoparticles in a wide temperature range. Surprisingly, we have observed the decreasing of the nanoparticles anisotropy constant in comparison to the bulk value expected for the material. We believe that this can be interpreted as due to both the migration of the Co2+ from octahedral to tetrahedral sites. © 2016 AIP Publishing LLC.


Silva L.S.,Nucleo de Pos Graduacao em Fisica | Silva L.S.,Federal University of Santa Maria | Peixoto E.B.,Nucleo de Pos Graduacao em Fisica | Mercena S.G.,Nucleo de Pos Graduacao em Fisica | And 3 more authors.
Materials Letters | Year: 2016

A sample of GdIn3 was obtained via the metallic flux technique and its structural, magnetic, and thermodynamic properties were studied. X-ray diffraction (XRD) measurements realized at room temperature were performed in order to verify whether the desired crystalline phase had been obtained. The experimental results show that single crystals were grown successfully by the employed growth technique. The magnetic characterization was carried out through magnetic susceptibility data as a function of temperature (2≤x≤300 K) and magnetic field (-7≤H≤7 T). The specific heat was measured using a commercial small mass calorimeter that employed the thermal relaxation technique in the temperature range of 2-200 K. © 2016 Elsevier B.V. All rights reserved.


Mendonca E.C.,Nucleo de Pos Graduacao em Fisica | Tenorio M.A.,Campus Prof. Alberto Carvalho | Mecena S.G.,Nucleo de Pos Graduacao em Fisica | Zucolotto B.,Nucleo de Pos Graduacao em Fisica | And 4 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2015

In this work, the effect of addition of different chelating agents on the magnetic properties of cobalt ferrite nanoparticles produced by the combining of both co-precipitation and hydrothermal methods is reported. The Rietveld analyses of X-ray diffraction patterns reveal that our samples are single phase (space group: Fd-3m) with small average sizes. The weight losses observed in the thermogravimetric measurements together with the M x H curves show that the organic contamination coming from chelating agent decomposition can give rise to misinterpretation of the magnetization measurements. Besides, analyses of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements and the M x H curves measured at room temperature allows us to state that both the average blocking temperature and particles size distribution are sensitive to the kind of chelating agent. © 2015 Elsevier B.V. All rights reserved.


Silva L.S.,Nucleo de Pos Graduacao em Fisica | Peixoto E.B.,Nucleo de Pos Graduacao em Fisica | Mercena S.G.,Nucleo de Pos Graduacao em Fisica | Coelho A.A.,University of Campinas | And 2 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2016

In this work, structural and magnetic data of YxGd1−xIn3 (0 < x < 0.5) single crystals grown from an In flux are reported. X-ray diffraction measurements carried out at room temperature reveal that all samples belong to cubic global symmetry (space group: Pm3m). Besides, the increasing of yttrium concentration produces a decreasing in the lattice parameter. The T-dependence of the magnetic susceptibility shows a peak which is related with the onset of an antiferromagnetic ordering. We believe that yttrium substitution must be decreasing the strength of interaction among magnetic moments of Gd displacing the magnetic transition into to low temperature region. Finally, MvsH loops measured at 2 K are almost linear independently of yttrium concentration. © 2015, Springer Science+Business Media New York.

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