The effectiveness of the electromagnetic excitation of ultrasound by ferrite powders was studied as a function of the defects of different origins and of temperature. For this purpose gamma-irradiated samples of single crystal manganese zinc ferrite (MZF) were investigated in solid solutions of iron yttrium garnet (IYG) in which some of the iron ions are replaced by non-magnetic aluminum ions. Results showed the possibility of choosing the optimum conditions (external magnetic field, ferrite powder composition, number of structural and radiation defects, temperature) for the practical realization of such an ultrasound transducers.