Barium ferrite(BaFe12O19)was elaborated and investigated in this work in terms of its capacitance-temperature characteristics. The curve taken at the fixed frequency of 1 kHz shows anomalous negative values of capacitance over the high-temperature regime. A complete analysis of this effect is carried out by performing ac measurements at various temperatures. The results indicate that a resonance phenomenon, arising from the external electrical circuit and shifting from the higher frequencies to the lower ones with increasing temperature, is responsible for this unusual effect. ©1997 American Institute of Physics.