The 4C variety of pyrrhotite shows a dramatic change in magnetic properties at T ≈ 30 K, known as the Besnus transition. Pyrrhotite, Fe 7S 8, is a common sulfide mineral in the Earth’s crust and mantle, as well as in a range of meteorites and is of interest to a wide variety of disciplines including economic geology, geophysics, and material science. We present an alternative and efficient method to produce large quantities of highly crystalline magnetite and cobalt ferrite nanoparticles using the Fe(III)-reducing bacterium, Geobacter sulfurreducens, at ambient temperatures through the extracellular dissimilatory reduction of Fe(III)-oxyhydroxides without and with addition of cobalt. It is not clear at present how this could be achieved using the highly regulated intracellular magnetosome systems. Although these previous studies are an important first step, in order to obtain the degree of control over the magnetic properties required by potential applications, Co must be incorporated into the spinel structure together with high nanoparticle yields. In particular, it is demonstrated here that cobalt ferrite (CoFe was synthesized in vitro, altering the magnetic properties of the material formed. A combination of electron microscopy, soft X-ray spectroscopy, and magnetometry techniques was employed to show that this method of biosynthesis results more » in high yields of crystalline nanoparticles with a narrow size distribution and magnetic properties equal to the best chemically synthesized materials. Here, the Fe(III)-reducing bacterium Geobacter sulfurreducens is used to synthesize magnetic iron oxide nanoparticles.

However, metal-reducing microorganisms offer an untapped resource to produce these materials.

To fabricate these materials purely using synthetic methods is costly in both environmental and economical terms. Such applications require the production of monodisperse nanoparticles with well-controlled size, composition, and magnetic properties. Nanoscale ferrimagnetic particles have a diverse range of uses from directed cancer therapy and drug delivery systems to magnetic recording media and transducers.

Copper tellurium