We report the synthesis and magnetic properties of frustrated Na0.22MnO2 center dot 0.39H(2)O and K0.6MnO2 center dot 0.48H(2)O with the birnessite structure. The structure, static, and dynamic magnetic properties of the compounds are investigated in detail. A combination of DC and AC magnetic susceptibility measurements and magnetization decay measurements reveal cluster glass behavior below the freezing temperature of 4 K for Na-birnessite and 6 K for K-birnessite. The frequency dependence of the freezing temperature is analyzed on the basis of dynamic scaling laws including the critical slowing-down formula and the Vogel-Fulcher law, which further confirm cluster glass formation in both compounds.
- AVERAGE OXIDATION-STATE
- PARAMAGNETIC RELAXATION