Structural and magnetic properties of NiFe2-xBixO4 (x=0, 0.1, 0.15) nanoparticles prepared via sol-gel method

NiFe2-xBixO4 (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe2-xBxO4 spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe2-xBixO4 have been investigated by means of Fe-57 Mossbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mossbauer spectroscopic measurements revealed that Bi3+ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe1-x Bi-x]O-4 = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe2-xBixO4 series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe2-xBixO4 nanoparticles were found to decrease with increasing degree of bismuth substitution. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.