The dielectric constant in a thermal phase transition magnetic material composed of rubidium manganese hexacyanoferrate observed by spectroscopic ellipsometry

In this work, the dielectric constant of rubidium manganese hexacyanoferrate was observed in the ultraviolet, visible, and near-infrared regions using spectroscopic ellipsometry (SE). The SE data for epsilon drastically varied with the phase transition between the high-temperature and low-temperature phases, e. g., the gain of the imaginary part of the dielectric constant (epsilon) changed 2900% at 520 nm. In a contrasting experiment, the dielectric constant in the 10(3)-10(5) Hz frequency range was also measured by an LCR meter and the gain factors of epsilon were approximately 30%. This large difference in the gain factors between SE and LCR methods is caused by the different resonance types, i.e., the SE method observes electronic resonance such as intervalence transfer band, while the LCR method observes dipolar resonance. The present work is the first SE observation of epsilon in metal complexes, and the epsilon data collected by an LCR meter are first to be observed in Prussian blue analogs.