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0 5 x 5 1) ferrites are investigated by ac conductivity measurements in the frequency range (10, to lo5 Hz) and the temperature range (300 to 950 K). The obtained conductivity results reveal the existence of a sum of two conductivity parameters adc and a,; and can be interpreted as the dc conductivity which is mainly due to excitations of electrons in localized states to the conduction bands, and to hopping conduction, respectively. All compositions exhibit a transition with a change in the slope of conductivity versus temperature curve. This transition temperature is found to decrease with increasing manganese content. All results are explained and discussed in terms of the magnetic and crystallographic behaviour of the compounds.

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