ESR of Tℓ 2+ Ions in KH 2 PO 4 and KD 2 PO 4 Crystals in Para- and Ferroelectric Phases

The ESR study of Tl2+ in KH2PO4 and KD2PO4 has been carried out. In ferroelectric phase the domain switching when applying the external electric field has been observed. The anisotropy of the hyperfine interaction of Tl2+ is shown to be caused by Tl2+ wave function overlapping with nearest oxygen ones.