Low-temperature sintering of Mg(Fe1-xMnx)2O4 (0≤x≤0.4) ferrite powders prepared via a citric acid route

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Fine spinel ferrite Mg(Fe1-xMnx)2O4 (0≤x≤0.4) powders for low-temperature sintering were prepared by the polymerized complex method. To prevent from agglomeration of nano-particles, aqueous ammonia (conc. 28 mass%) was added into the metal-citrate complex. Precursors were heated at 873 K for 2 h in air to burn-out the organic substances and calcined at 973 K for 2 h under a 3%H2-N2 atmosphere to make the powders reductive. Then, dense powder compacts were sintered at 1273 K for 2 h in a 5%O2-N2 gas flow. Thus fabricated single-phase ferrite ceramics with the relative density of ~95% revealed homogeneous microstructures consisting of fine grains (~250 nm). Their magnetic permeability m (at room temperature), saturation magnetization ss (at 10〜800 K) and Curie temperature Tc were measured. For x=0.2 specimen, the values of m (27.4 at 10 MHz), ss (45.6 emu·g-1 at 300 K) and Tc (~750 K) were attained. Nevertheless their small grain size, these ceramics exhibited relatively high m and ss; this might be due to the homogeneous grains derived from the liquid phase powder preparation.
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