On low-temperature phase transitions in the $CoFe_2O_4$ and $MnFe_2O_4$ spinel ferrites

The data obtained in the studies on the temperature dependences of magnetization, magnetostriction, thermal expansion, magnetic anisotropy constant, and magnetoresistance for the $CoFe_2O_4$ and $MnFe_2O_4$ spinel ferrites are presented. The curves display anomalous behavior (maxima, inflections, etc.) below the Curie temperatures. The data suggest that ferrites with the spine! structure have several low-temperature structural and magnetic phase transitions. By low-temperature phase transitions we mean phase transitions at temperatures below the Curie point.