Cerous magnesium nitrate: A magnetic temperature scale 0.002−2°K

Abstract

Isentropic demagnetizations from known starting conditions yielded a determination of the entropy-magnetic susceptibility, or $S\text{−}\mathrm{\chi }$, relation for single-crystal spheroids of the paramagnetic salt cerous magnesium nitrate, CMN. Enthalpy differences, $\mathrm{\Delta }Q$, between the low temperature end-points thus reached and an (arbitrary) reference temperature near $\mathit{1}°K$ (determined by gamma ray heating) yielded a corresponding $Q\text{−}S$ curve, whence one obtained $S\text{−}T$ and $\mathrm{\chi }\text{−}T$ relations, $T$ being the thermodynamic temperature. The salt exhibits a broad maximum in $\mathrm{\chi }$ centered on $S/R=\mathit{0.32}$, for which region the absolute temperature is determined to be ${\mathit{0.001}}_5°K$. Our results disagree significantly with those of other workers (even $S\text{−}\mathrm{\chi }$, which is not subject to large experimental error) save for the observation that CMN obeys the Curie law at least down to $\mathit{0.006}°K$.