Magnetic Susceptibility of FeCl2·4H2O at Low Temperatures

The magnetic susceptibility of powdered ${\mathrm{FeCl}}_2\text{·4}{\mathrm{H}}_2\mathrm{O}$ has been measured between 1.3° and 4.2°K and from 14° to 21°K by an ac mutual-inductance method. A maximum, apparently associated with an anti-ferromagnetic-paramagnetic transition, is found near 1.6°K. In the hydrogen region, a Curie-Weiss law is obeyed, the Curie constant yielding a splitting factor $\text{g\hspace{0.17em}=\hspace{0.17em}2.19}$ for the ${\mathrm{Fe}}^{\mathrm{++}}$ ion if its effective spin is assumed to be $\text{S\hspace{0.17em}=\hspace{0.17em}2}$ .