Low-temperature synthesis and microstructure-property study of single-phase yttrium iron garnet (YIG) nanocrystals via a rapid chemical coprecipitation

Single-phase yttrium iron garnet (Y3Fe5O12, YIG) nanocrystals have been synthesized via a rapid chemical coprecipitation process with reverse strike operations, followed by calcining the precipitates at the temperature around 750 degrees C. The formation of YIG nanocrystals from the amorphous precipitates and their microstructural features and magnetic properties were investigated by FT-IR, XRD, TG-DSC, FESEM, TEM and VSM. It has been found that the as-obtained precipitates could be thermally activated to directly form the crystalline phases of garnet structure around 650 degrees C, including cubic YIG and minor tetragonal YIG but no trace of YFeO3, which was often involved during the synthesis of YIG or doped-YIG when a chemical coprecipitation method was used. The calcinations could make the tetragonal YIG entirely transform into the cubic phase at 750 degrees C and allow the crystallites of the latter to grow from similar to 22 nm to similar to 50 nm in size almost linearly as a function of the temperature ranging from 650 degrees C to 900 degrees C. Moreover, the room temperature saturation magnetization of the samples after calcinations at various temperatures showed a nonlinear increase from 0.24 emu g(-1) to 24.54 emu g(-1), which should be associated with the alignments of atomic magnetic moments in the materials from completely-disordered to partially-ordered firstly and further to completely-ordered and, in the last stage, mainly with the growing YIG nanocrystals. (C) 2010 Elsevier B.V. All rights reserved.