Low-Temperature Magnetic Susceptibilities of Some Hydrated Formates of Cu++ and Mn++

The magnetic susceptibilities of powdered specimens of Cu(HCO2)2·4H2O, Cu(HCO2)2·2H2O, and Mn(HCO2)2·2H2O have been measured by an audio-frequency mutual-inductance method between 1.3° and 4.2°K, and from 14° to 20°K. At hydrogen temperatures Cu(HCO2)2·2H2O and Mn(HCO2)2·2H2O exhibit Curie—Weiss behavior which, however, breaks down significantly in the helium region. The susceptibility of Cu(HCO2)2·4H2O rises to a pronounced peak at 16.8°K and is essentially constant below 4.2°K. The susceptibilities of single-crystal Cu(HCO2)2·4H2O were measured along the three monoclinic axes in the same temperature intervals. χc and χb show sharp maxima at 16.8°, and are much larger in magnitude than χa. The possibility of this salt becoming weakly ferromagnetic below 16.8°K is considered, as is the unusual indirect-exchange coupling of Cu++ moments via formate groups.