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Itabaiana, Brazil

MacHado E.S.,Campus Prof. Alberto Carvalho | Adorno A.T.,Sao Paulo State University | Magdalena A.G.,Sao Paulo State University | Carvalho T.M.,Sao Paulo State University
Journal of Thermal Analysis and Calorimetry

The completeness of b-phase decomposition reaction in the Cu-11wt%Al-xwt%Ag alloys (x =0, 1, 2, and 3) was studied using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and optical microscopy (OM). The results indicated that b-phase transformations are highly dependent on cooling rate and on the presence of Ag. On slow cooling, the silver presence prevents the b-and b1-phase decomposition; thus, inducing the martensitic phase formation. After rapid cooling, a new thermal event is observed and the reverse martensitic transformation is shifted to lower temperatures. © Akadémiai Kiadó, Budapest, Hungary 2011. Source

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

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. Source

Jesus C.B.R.,Campus Prof. Aluisio de Campos | Mendonca E.C.,Campus Prof. Alberto Carvalho | Silva L.S.,Campus Prof. Aluisio de Campos | Folly W.S.D.,Campus Prof. Alberto Carvalho | And 2 more authors.
Journal of Magnetism and Magnetic Materials

Magnetization data on the bulk ZnFe2O4 antiferromagnetic compound (TN≈10 K) obtained via solid state reaction at different synthesis temperatures show one weak ferromagnetic component at room temperature. We have related it with the cationic disorder effect present on spinel structure of our bulk samples which comes from the magnetic interaction between iron ions sit on both octahedral and tetrahedral sites. The magnetization measurements show to all samples a clear peak around 10 K consistent with the antiferromagnetic phase transition. On the other hand, after extracted the paramagnetic component, the hysteresis loops measured at room temperature display one weak ferromagnetic component. Once the T-dependence of magnetization does not fit to a Curie-Weiss law to temperatures well above the magnetic transition we have used a combination of the Curie-Weiss law (paramagnetic spins) and a typical temperature dependence of M0, M0(T)=M0(0)[1-(T/TC)2] 0.5 (ordered ferromagnetic spins). We note an increase of the M 0(0) as function of the synthesis temperature. This reinforce our supposition of a cationic disorder effect driving the system to present two kinds of magnetic interactions between iron ions on A and B sites. © 2013 Elsevier B.V. Source

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