Rigorous ESR spectroscopy of Fe3+ impurity ion with oxygen vacancy in ferroelectric SrTiO3 crystal at 20 mK

Impurity Fe3+ ion electron spin resonance (ESR) spectroscopy using multiple dielectric modes in a SrTiO3 dielectric resonator has been performed with a tunable DC magnetic field of up to 1.6 T. The Ti-4 +(d(0)) ion is substituted by Fe3+ ion forming FeO6 octahedral complex with an iron-oxygen-vacancy (Fe3+- V-O). In such a metal-ligand complex, a giant g-factor of g(parallel to F) = 5.51 was observed in the ferroelectric phase at 20 mK. The change of Fe3+ ion center-symmetry in the FeO6 complex as a soft-mode characteristics of ferroelectric phase transition and the influences of iron-oxygen-vacancy (Fe3+- V-O), are interactively sensitive to asymmetry in the octahedral rotational parameter Phi in SrTiO3 .