FINE-STRUCTURE AND MAGNETIC-PROPERTIES OF MN-DOPED AND CO-DOPED NANOCRYSTALLINE GAMMA-FE2O3

High resolution TEM (HRTEM), Mossbauer spectroscopy and SQUID magnetom etry were utilized to study the fine structure of equiaxed, Mn- and Co -doped gamma-Fe2O3 nanocrystals with a particle size of 30-50 nm. The allocation of cation distribution, based on a redox mechanism and know n cation site preferences is 93+)[Nn0.074+Mn0.163+Co0.342+Fe1.23+squar e0.20]O4, in which square is the vacancy, is the A site, and [..] is t he B site. This leads to an Fe occupancy ratio of B sites to A sites o f 1.38, as verified by Mossbauer spectroscopy. The calculated saturati on magnetic moment of 2.99 mu(B)/MF is very close to the measured 2.84 mu(B)/MF. HRTEM micrographs of the air-cooled nanocrystals fits well with the simulated lattice images using the proposed cation distributi on (without directional ordering). While the HRTEM micrograph of the c ore of an annealed nanocrystal are not in good agreement. This is thou ght to arise from directional ordering inside the annealed particles.