The loss properties of some rings of manganese zinc ferro ferrites, with varying Fe2+contents, have been measured as a function of flux density, frequency, and temperature. At any frequency or temperature the loss factor and the hysteresis coefficient have a linear relationship for the samples which suggests the presence of an effective friction or viscosity field (or aftereffect field). Extrapolation to results in a positive loss . This nonhysteresis loss has a large frequency dependent component which is proportional to temperature and which cannot be accounted for by eddy-current losses in the material. There appears to be, by extrapolation, a large nonhysteresis loss at zero frequency. The variability of and ηBis examined. The increases in loss after capacitor discharge demagnetization are found to be much greater than the corresponding increases in permeability. Results of the experiments are discussed in terms of the Néel after effect theory.