Magnetism and phase transition for CoFe2-xMnxO4 nanocrystalline thin films and powders

CoFe2-xMnxO4 (x = 0-2.0) nanocrystalline thin films and powders were prepared by a sol-gel process. The crystal structures and magnetic properties of the as-synthesized products were identified by an X-ray diffractometer (XRD) and an alternating gradient magnetometer (AGM), respectively. XRD analysis reveals that COFe2-xMnxO4 nanocrystalline films and powders occurred during a cubic-to-tetragonal phase transition when x = 1.5 and 1.3, respectively. The substitution of Mn3+ for Fe3+ causes the migration of Co2+ from A to B sites, and finally lead to the phase transition. AGM investigations indicate that M-S, T-C and He values decrease with increasing Mn content x. The decrease of M-S and T-C is related to the weakly magnetic property of Mn3+; whereas, the decrease of He is ascribed to the content decrease of Co2+ on the B sites. The large He around the phase transformation point is induced by a structural stress originated from the metastable cubic structure. (C) 2002 Elsevier Science B.V. All rights reserved.