Calorimentric investigation of heat capacity of the $\mathrm{ErMFe}_2\mathrm{O}_{5.5}\,(\text{M} = \mathrm{Mg}$, $\mathrm{Ca}$, $\mathrm{Sr}$, $\mathrm{Ba})$ ferrites in the temperature range of $298.15$–$673$ K and calculation of their thermodynamic functions

We present the data of the calorimetric investigations of the $\mathrm{ErMFe}_2\mathrm{O}_{5.5}\,(\text{M} = \mathrm{Mg}$, $\mathrm{Ca}$, $\mathrm{Sr}$, $\mathrm{Ba})$ ferrites and calculation of their thermodynamic functions. As a result of calorimetric studies of the heat capacity, within the temperature range of $298.15$–$673$ K, we discover, at the curves of the $C_p \sim f(T)$ dependence, the second kind $\lambda$-shaped phase transitions at the following temperatures: $373$ K – $\mathrm{ErMgFe}_2\mathrm{O}_{5.5}$, $398$ K – $\mathrm{ErCaFe}_2\mathrm{O}_{5.5}$; $423$ K – $\mathrm{ErBaFe}_2\mathrm{O}_{5.5}$, $398$ K – $\mathrm{ErSrFe}_2\mathrm{O}_{5.5}$. We derived the equations of the temperature dependence of the heat capacity for the ferrites with account for these phase transformations.