The temperature dependence (300°K to 40°K) of the magnetic susceptibility of the following ${\mathrm{Mn}}^{++}$ salts has been measured: MnO, MnS, MnSe, MnTe. A $\lambda$-point transition at low temperatures makes the susceptibility break away from a Weiss-Curie law and decrease with lowering temperatures. Each salt has its characteristic transition temperature, increasing with increasing molecular weight. Evidence for field dependence of the susceptibility and for magnetic hysteresis has been found. It seems likely that an exchange force is the cause of the transition from paramagnetism to antiferromagnetism.

• Received 13 July 1939

DOI:https://doi.org/10.1103/PhysRev.56.922