Variation of the Principal Magnetic Susceptibilities of Certain Paramagnetic Crystals with Temperature

Abstract

Curie and Weiss Constants for the Principal Susceptibilities of Certain Crystals. The Curie and Weiss constants, respectively ${C}_{m}$ and $\ensuremath{\Delta}$ of the equation ${x}_{m}=\frac{{C}_{m}}{(T+\ensuremath{\Delta})}$, over the temperature range 60\ifmmode^\circ\else\textdegree\fi{} to -45\ifmmode^\circ\else\textdegree\fi{}C have been determined for 5 crystals of the isomorphic monoclinic double sulphate series [M ${\mathrm{R}}_{2}$${(\mathrm{S}{\mathrm{O}}_{4})}_{2}$ 6${\mathrm{H}}_{2}$O] containing cobalt, nickel, or copper, and for cobalt sulphate heptahydrate. The measurements were made by Rabi's method of determining the principal magnetic susceptibilities of crystals, which was found applicable over this temperature range. The use of ethyl alcohol as a solvent for the auxiliary paramagnetic salt permitted the extension of the method to temperatures below the freezing point of water solutions, such as those used by Rabi, for crystals of volume susceptibilities less than 35\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$. The lower limit of the applicability of the method depends only on the availability of low freezing point solutions of sufficient susceptibility. In general the Curie constants for the principal susceptibilities of any given crystal were very nearly the same. The Weiss constant showed considerable variation, both between the different principal magnetic axes of the same crystal, and from one crystal to another. Both the Curie and Weiss constants decreased progressively as the metal ion was changed from cobalt to nickel to copper. The effect of change in the alkali ion from N${\mathrm{H}}_{4}$ to potassium was less pronounced, although there was a slight tendency for the Curie constant to increase and for the Weiss constant to become more positive. The accuracy claimed for the measurements is 1 percent. In general there was a small continuous change in the orientation of the principal magnetic axes in the plane of symmetry of the crystal with respect to the crystallographic axes as the temperature was varied.