ESR Study of the Ferroelectric Phase Transition in CsH₂PO₄

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Two kinds of AsO₃²⁻ radicals were found in the electron spin resonance (ESR) spectra of γ-irradiated CsH₂PO₄ including a small amount of AsO₄³⁻. The splitting of the spectral line below T_c represents a rotation of AsO₃²⁻ radical and the temperature dependence is represented by the formula A(T_c–T)^β with β=0.32±0.05 in the range from T_c–5° to T_c–0.7°. Meanwhile from the analysis of the ESR spectra of CsH₂PO₄ doped with Cr³⁺, it was found that the Cr³⁺ ion replaced Cs⁺ ion and two protons near the Cs⁺ site were vacant. Anomalous change of the breadth of the spectral line which was related with the slowing down of spin-lattice relaxation time was observed around T_c. The correlation time of the magnetic fluctuation was estimated to be about 1.7×10⁻¹¹ sec at T_c±2°.