Altering the magnetic and dielectric responses of polycrystalline gadolinium iron garnet by Al substitution

In our study, we have synthesized Gd3Fe5−xAlxO12 garnet samples with x=0.0 to 0.6 from solid-state reaction method. The Rietveld refinement of XRD data reveals the garnet phase formation and allows us to determine the lattice parameters, bond length and bond angles. We found that the lattice constant is decreased from 12.4938Å to 12.4666Å as the Al concentration increased. The average grain size is found to decrease as x is increased from 0.0 to 0.6 and it leads to larger grain boundary volume and hence provides more resistance. The ferrimagnetic transition temperature is dropped from 561K to 524K with the increase in Al concentration from x=0.0 to 0.6. This reduction in transition temperature is attributed to the weakening of super-exchange interaction between Fe(a)−O−Fe(d) networks. Interestingly, we also observed a magnetic compensation at around 293K for the parent compound, which is disappeared in Al-doped samples. The low saturation magnetization of the parent sample at room temperature is enhanced by Al doping. We have obtained the dielectric constant of the order of 104 at lower frequency regime which shows a decreasing trend with increase in frequency for all the samples of Al-GdIG series. In addition to this, low dielectric loss at room temperature is observed, indicating their potential usefulness in microwave devices.