Abstract
A series of Ca-doped yttrium iron garnet ceramics (Y3-xCaxFe5O12 (x = 0, 0.05, 0.1, 0.15, 0.2)) were prepared by the solid state method. The structure, morphology, valence fluctuation, thermal analysis, magnetization, magnetodielectric and Mössbauer spectrum of Y3-xCaxFe5O12 ceramics were systematically studied. All of the samples crystalized as single phase of garnet structure with the grain sizes of 2–3 μm. The temperature dependent percentage weight loss and heat flow were investigated by thermogravimetric (TG) and differential scanning caborimetry (DSC). The structure of Y3-xCaxFe5O12 ceramics was studied by XRD, Raman and Infrared (IR) spectra. The results indicated that Ca2+ substitution leads to lattice expansion and presence of Ca–O octahedron, which causes the concentration of Fe2+ decrease and Fe4+ increase. As a result, the saturation magnetization first increases and then decreases with the increase of Ca concentration. A six lines asymmetry of magnetic components were observed in Mössbauer spectrum, which was fitted by two hyperfine magnetic sextets corresponding to tetrahedral and octahedral sites, respectively. With the increase of Ca concentration, the intrinsic magnetodielectric (MD) effect disappears completely due to the dramatic decrease of Fe2+-Fe3+ dipoles. Fe3+-Fe4+ dipoles do not contribute to the MD properties of Y3-xCaxFe5O12 ceramics due to the lack of the defects such as electrons or holes being used as media.
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