Role of silver nanoshells on structural and magnetic behavior of Fe3O4 nanoparticles

The structural and magnetic behavior of monodispersed uncoated Fe3O4 nanoparticles (average particle size = 6 nm) and silver coating of mean thickness 1.5 nm and 2 nm prepared in an emulsion was investigated. The structural and magnetic analysis indicated the formation of a tri layer structure comprising of a disordered magnetic layer of diffused core present in between magnetic core and non-magnetic shell. The nanocrystals with thicker nanoshells exhibit superparamagnetic properties showing decrease in blocking temperatures with increasing shell thickness, whereas the particles of larger diameter are ferrimagnetic at room temperature. The value of saturation magnetization are smaller than those obtained for bulk magnetite emphasizing the presence of a disordered spin layer due to unsaturated iron ions at the surface in case of uncoated magnetite nanoparticles and at the interface for coated ones. The spin canting at the interface, surface strain and increased magnetoelastic anisotropy are some other factors influencing the magnetic properties of these nanoparticles.