Heat capacity investigation of dopant effects on the magnetic disordering temperature in Fe3O4†

The heat capacities of ZnFe₂O₄, Zn_0.005Fe_2.995O₄, Zn_0.066Fe_2.934O₄, and Cd_0.010Fe_2.990O₄ were measured over the temperature range of 350–1000 K by means of differential scanning calorimetry. The temperatures at which the maximum in heat capacity occurs due to the ferrimagnetic anomaly in the doped-Fe₃O₄ samples were found to decrease with increasing dopant. The excess entropy associated with the ferrimagnetic anomaly was estimated using three methods. One method, used previously for Fe₃O₄, employed a calculated lattice contribution for Fe₃O₄. The other two methods used the experimentally determined heat capacity of ZnFe₂O₄, either unmodified or mass adjusted, to approximate contributions from lattice vibrations.