Abstract
Magnetic heat-capacity anomalies of deerite and grunerite, both of which are silicate minerals containing Fe ions, were resolved by using the new isometric molar lattice heat-capacity formula. In the process of the resolution, apparent θKW, the single fitting parameter contained in the formula, was evaluated from the experimental heat-capacity data, and since the apparent θKW was nearly constant for the heat capacity at higher temperatures where the lattice contribution is dominant, the constant value of θKW was utilized to estimate the lattice heat capacity at low temperatures. The resulting heat-capacity anomaly of deerite was composed of a main peak centered at about 16K which resembles a Schottky anomaly and a symmetric sub-peak centered at about 34K. The heat-capacity anomaly of grunerite which has a sharp peak at 35.5K was found to show a curvature change in the high-temperature side of the slope. The feature is qualitatively explainable by the randomly diluted Ising model. It treats random disruption of spin interaction by non-magnetic ions such as Mg ions which replace a portion of Fe ions.
