Superparamagnetism in Bi0.95Mn0.05FeO3 - Ni0.5Zn0.5Fe2O4 multiferroic nanocomposites

Multiferroic nanocomposites of x.Bi0.95Mn0.05FeO3 + (1-x).Ni0.5Zn0.5Fe2O4, for x values of 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1, have been fabricated using sol-gel autocombustion and solid state methods. Structural and microstructural studies reveal the formation of parent phases of perovskite and spinel, while ensuring proper mixing of two phases by showing clear grain growth in the composites, respectively. Magnetic (M-H loop) measurements show that there is an enhanced magnetic order in the nanocomposites. Besides, the investigated nanocomposite materials exhibit superparamagnetic behaviour with small coercivities in the order of 3-29 Oe in all the samples. This may be due to strong influence of both the phases on one another to modify the anti-ferro magnetic (AFM) order in manganese doped bismuth ferrite. The observed magnetic behaviour was attributed to nanoparticle nature of the composites. In order to ensure the same, crystallite sizes were estimated using Langevin distribution function as well as X-ray diffractometry (XRD), which lie in the range between 28.51 and 55.43 nm, and the obtained results show a good agreement between them. The interpretations of these results are obviously evolved from the structural contributions for ferroelectricity, antiferromagnetic spin spiral cycloid structure around the FeO6 octahedra, weak ferrimagnetic exchange interactions between the cations located at A- and B-sites and the possible interplay between different ferroic orders.