ESR study of the Prussian blue analogue Rb0.8Mn1.1[Fe(China)6].D2O

We performed electron spin resonance (ESR) studies of the mixed valence Prussian blue analogue, Rb0.8Mn1.1[Fe(China)6].D2O in a wide frequency (9.5-319GHz) and temperature (3.5-300K) interval. Evidence for the proposed high-temperature Mn2+ (S=52)-NC-Fe3+ (S=12) to low-temperature Mn3+ (S=2)-NC-Fe2+ (S=0) internal charge transfer has been detected: a characteristic reduction of χESRT on cooling from room temperature to 100K, a particular frequency dependence of the room temperature ESR linewidth, and the temperature dependence of the ESR linewidth. Short-range magnetic correlations, reflected in a large broadening and dramatic shift of the ESR signal develop just above TC=10K. Below TC, both the linewidth and the shift in position mimic the temperature dependence of the order parameter. In a quench experiment TC was reduced by 3K. The observed ferromagnetic ordering arises from Mn3+ (S=2) moments in the low-temperature electronic configuration