Magnetic susceptibility and heat-capacity studies of single crystals: A study of transitions at nonzero temperature

Heat-capacity and magnetic-susceptibility studies have been carried out on (Formula presented) single crystals for (Formula presented) and (Formula presented) respectively. These and earlier physical measurements document the gradual evolution, with rising (Formula presented) of the alloys from good insulators to poor metals at low temperatures. The transitions between various magnetically ordered or disordered phases are marked by anomalies in these physical measurements. The trend of magnetic susceptibility with temperature indicates that alloys near the crossover to the highly correlated metallic state exhibit increasing charge-carrier localization with rising temperature; this is ascribed to the dominance of entropic contributions to the free energy. It is stressed that these variations in properties are achieved by isoelectronic substitutions in the anion sublattice that leave the cation sublattice undisturbed.