The magnetic particle spectrum (MPS) of bacterial magnetosomes, isolated from Magnetospirillum gryphiswaldense, is measured and compared to that of the current “gold standard”, Resovist®. It is shown that the amplitudes of the magnetosomes’ harmonics by far exceed that of Resovist®; the amplitude of the third harmonic is higher by a factor of 7, and is the highest value obtained for iron oxide nanoparticles to date.

Novel Fe₃C-based nanostructures with an inner layered structure have been synthesized by a simple medium-temperature (T = 700 °C) process based on carbothermal reduction. In this process, the iron precursor reacts with a selected nitrogen rich carbon source (namely, 4,5-dicyanoimidazole) to form wrapped nano-sheets of Fe₃C@C(N). The nanosheets are composed of 5 nm crystalline Fe₃C nanoparticles, which are integrated into a nitrogen-doped carbon phase giving rise to the wrapped morphology. By variation of reaction parameters (such as initial concentration, temperature, reaction time), the typical accompanying side products of iron carbide such as metallic iron and amorphous carbon can be kept very low or even avoided. Contrary to simple expectations, those nanostructures are surprisingly robust against oxidation in air and could have potential applications in nanomagnetism and catalysis.

Mesoporous Fe₃C is synthesised by combining a hard-templating approach with carbothermal reduction. The product shows high crystallinity, a transport pore size of d ≈ 20 nm and high specific surface area (415 m² g⁻¹). Its usefulness is exemplified by its catalytic activity and high stability in NH₃ decomposition.