The dielectric and magnetic properties of mixed magnetoelectric ( x )Mn_0.4Zn_0.6Fe_2O_4–(1 – x ) · PbZr_0.53Ti_0.47O_3 ( x = 0, 0.1, 0.2, 0.3, 0.4, and 0.8) composites have been studied in the temperature range near the ferroelectric and magnetic phase transitions. The influence of the composite compositions on the thermodynamic parameters of the initial phases of the composites has been revealed. It is found that the reason for this influence is the mutual doping of the composite phases that takes place during high-temperature sintering of powders of ferrite Mn_0.4Zn_0.6Fe_2O_4 and ferroelectric PbZr_0.53Ti_0.47O_3.