Effects of In3+-substitution on the structure and magnetic properties of multi-doped YIG ferrites with low saturation magnetizations

Multi-doped YIG ferrites {Y1.7Gd0.5Ca0.8}[Fe2-xInx](Fe2.15V0.4Mn0.05Al0.4)O-12 (x=0, 0.3, 0.6, 0.7, 0.8 and 0.9) with low saturation magnetizations (4 pi M-s=400-600 G at 298 K) were prepared by a conventional ceramic technology and the effects of In3+-substitution on their structures and magnetic properties were systematically investigated using XRD, SEM and VSM. It has been found that as-synthesized powders and sintered ferrites showed a single-phase of garnet structure with a cell parameter (a) that increased linearly with increase in In3+ concentration from x=0 up to 0.9. Apparent relative densities of sintered samples were all over 98%, but no remarkable influences of In3+-substitution were observed by SEM on the refinement of crystal grains and the enhancement of sintering of ferrites. In addition, the Curie temperature T-c decreased almost linearly as In3+ concentration increased, while the corresponding saturation magnetization at room temperature presented a variation characterized by a gradual increase first and then a rapid plunge. On the basis of quantitative analysis of XRD data and the theory on super-exchange interactions, it has been established that the incorporated In3+ ions via doping were exclusively located at the sites with octahedral coordinations in the crystal structure and the aforementioned magnetic properties can be simply attributed to weakening super-exchange interactions between neighboring magnetic ions through oxygen ions due to the "dilution effect" of added non-magnetic In3+ ions. (C) 2010 Elsevier B.V. All rights reserved.