Anomalous Temperature Dependence of Exchange Interactions in K2CuCl42H2O and K2CuCl42D2O

Exchange interactions between two dissimilar Cu 2+ ions in K 2 CuCl 4 2H 2 O and K 2 CuCl 4 2D 2 O were investigated by means of electron paramagnetic resonance (EPR). The measurements were done in the frequency range from 9.3 to 65.8 GHz between 10° and 370°K. An amalgamated single line was observed below 200°K but the line splits into two lines near room temperatures. Considering the frequency and temperature dependence of the phenomenon, it is concluded that the exchange interaction depends strongly on temperature. The magnitude of the exchange interaction J / k (°K) varies from 0.3 to 0.08 between 4° and 300°K. Similar temperature dependence was obtained in K 2 CuCl 4 2D 2 O and the exchange interaction in this compound was found to be about 0.02°K larger than of K 2 CuCl 4 2H 2 O.