Anomalous Temperature Dependence of D Tensor in the ESR Spectrum of Fe³⁺ Ions Doped in KDP and DKDP Crystals

Abstract

ESR spectra of Fe³⁺ ions doped in KDP and DKDP crystals were studied. The D tensor for Fe³⁺ ion in KDP crystal was distinctly different from that in DKDP in the temperature dependence, especially when the magnetic field was parallel to the c-axis. The origin of the difference was investigated by considering the dynamical contribution from the ferroelectric soft mode.
The analysis showed that the difference was mainly caused by the change of the coefficient of the temperature dependent term in the dispersion relation of the soft mode. The comparison with the theoretical model proposed by Kobayashi suggests that the tunneling frequency of deuteron in DKDP (90∼95% deuterated) is a third of, or a little more smaller than that for KDP.