Mossbauer study of copper-manganese ferrites in an external magnetic field

The copper-manganese ferrite series Cu 1-x Mn x Fe 2 O 4 (x=0.0-0.8) has been studied by the Mossbauer effect technique at 4.2K in an external magnetic field of 4.2 T, applied parallel to the direction of the gamma rays. The cation distributions and the hyperfine magnetic fields at 57 Fe nuclei in A and B sites have been determined. For the manganese-rich compositions, a part of the manganese at the B site is present in a trivalent state along with an equal amount of iron in a divalent state. The manganese-rich compositions have a collinear spin structure and the copper-rich compositions have a very small canting of spins. The distribution of hyperfine fields at the B site has been analysed in terms of supertransferred hyperfine fields from neighbouring ions. The centre shifts are found to be independent of the sample composition.