Structural and magnetic properties of Al-doped yttrium iron garnet ceramics: 57Fe internal field NMR and Mössbauer spectroscopy study

The structural and magnetic properties of Al substituted yttrium-iron garnet (Y3AlxFe5-xO12, x = 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8) ceramic powders synthesized using solution combustion method were investigated. Post combustion, the samples were calcination at 1045 °C for 6 h and subsequently at 1200 °C for 6 h to obtain phase-pure garnets. X-ray diffraction (XRD) results confirm the formation of garnets with Ia3¯d structure. The occupancy of Y3+ ions in the dodecahedral site and the distribution of Al3+ and Fe3+ ions in the tetrahedral and octahedral sites in the bcc structure of the garnet were confirmed by Rietveld refinement of XRD patterns, Mössbauer spectroscopy and 57Fe internal field NMR spectroscopy. For low Al content, Al3+ ions have preference to occupy tetrahedral (Td) sites than the octahedral (Oh) sites. At higher Al content the distribution of Al tends towards a ratio of 3:2 at the tetrahedral:octahedral site. Increase in Al doping results in the decrease in the lattice parameter due to smaller size of Al3+ as compared to Fe3+ ion. All the studied samples show coral-network-like surface morphology. The saturation magnetization (MS) values decrease from ∼26.94 emu/g to ∼ 0.17 emu/g with increase in Al content from 0.0 to 1.8. Further addition of Al makes the sample paramagnetic at RT. Substitution of non-magnetic Al3+ reduces the saturation magnetization rapidly due to the decrease in the superexchange interaction in the crystal.