Magnetic properties of bio-synthesized zinc ferrite nanoparticles

► The magnetism of bio-zinc ferrite compared with chemically synthesized materials. ► A metal reducing Thermoanaerobacter, TOR-39 produced nanoparticulate zinc ferrites. ► Crystallite size decreased with more Zn substitution. ► Lattice parameter and the unit cell volume increased with more Zn substitution. ► Saturation magnetization of the bacterially synthesized zinc ferrites was increased.