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    Magnetic and dielectric properties of Bi3+ substituted SrFe12O19 hexaferrite
    (Elsevier B.V., 2016) Auwal, İsmail A.; Erdemi, Hamit; Sözeri, Hüseyin; Güngüneş, Hakan; Baykal, Abdulhadi
    In the present study, SrBixFe12?xO19 (0.0?x?1.0) nanomaterials were successfully synthesized by using chemical co-precipitation method. Products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating sample magnetometer (VSM), Mössbauer spectroscopy, AC conductivity and dielectric measurements. The crystal structural information studied by X-ray diffraction (XRD) indicated the formation of single phase pure hexagonal structure, while electron-dispersive X-ray spectroscopy (EDX) revealed the stoichiometric ratio among Bi, Sr, Fe elements. The crystallite sizes of the products were in the range of 65–82 nm. VSM analysis showed a tendency in saturation magnetization as Bi2O3 concentration raises, which can be ascribed to preferential site occupied by Bi3+ ions. The frequency-dependent ac conductivity plots exhibited similar trends for all samples. A significant temperature-dependent behavior was only observed at low and medium frequencies. The replacement of non-magnetic Bi3+ ions by Fe3+ ones having magnetic moment of 5 µB decrease the magnetic moment of 4f1 site. The AC conductivity increases with frequency as hopping of the charge carriers increases between Fe2+and Fe3+. The DC conductivity exhibited an improvement with increasing temperature and Bi content, and the highest conductivity was measured as 2.84×10?9 S cm?1 for x=0.8 at 120 °C. The variation of dielectric constant, dielectric loss and tangent loss was observed with the frequency and temperature due to change of electrical conductivity as x changes.
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    Synthesis and magneto-electrical properties of MFe2O4 (Co, Zn) nanoparticles by oleylamine route
    (Elsevier Ltd, 2016) Kurtan, Ümran; Erdemi, Hamit; Baykal, Abdulhadi; Güngüneş, Hakan
    In this study, nearly monodisperse cobalt ferrite (CoFe2O4) and zinc ferrite (ZnFe2O4) nanoparticles (NPs) without any size-selection process have been fabricated through an alluring method in an oleylamine (OAM)/benzyl ether system. Samples were synthesized by thermal decomposition of metal acetylacetonates in a high-boiling solvent and in the presence of oleylamine as surfactant and reducing agent. XRD analysis confirmed the purity and nanosized of both products and TEM analysis showed the monodispersion of them also. The oleylamine coated nanoparticles exhibited semiconducting nature at lower frequencies i.e. conductivity enhances with temperature. The dc conductivity curves of ZnFe2O4@OAm and CoFe2O4@OAm NPs indicate significant temperature-dependent behavior. The temperature and frequency-dependent variations of dielectric loss (??) of MFe2O4@OAm NPs display an almost sharp exponential decrease with frequency which becomes more considerable at higher temperatures and at low at low frequency regime. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been determined. Although the Mössbauer spectra for the ZnFe2O4@OAm consists only one paramagnetic central doublet and CoFe2O4@OAm NPs have also one paramagnetic doublet and three magnetic Zeeman sextet.