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Magnetotactic bacteria benefit from their ability to form cellular magnetic dipoles by assembling stable single-domain ferromagnetic particles in chains as a means to navigate along Earth's magnetic field lines on their way to favorable habitats. We studied the assembly of nanosized membrane-encapsulated magnetite particles (magnetosomes) by ferromagnetic resonance spectroscopy using Magnetospirillum gryphiswaldense cultured in a time-resolved experimental setting. The spectroscopic data show that 1), magnetic particle growth is not synchronized; 2), the increase in particle numbers is insufficient to build up cellular magnetic dipoles; and 3), dipoles of assembled magnetosome blocks occur when the first magnetite particles reach a stable single-domain state. These stable single-domain particles can act as magnetic docks to stabilize the remaining and/or newly nucleated superparamagnetic particles in their adjacencies. We postulate that docking is a key mechanism for building the functional cellular magnetic dipole, which in turn is required for magnetotaxis in bacteria.

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The glass-forming ability of Fe-based metallic glasses has a direct relationship with their metalloid content. A good glass-former usually needs a metalloid content of approximately 20at.%. However, a high metalloid content causes deterioration not only in magnetic properties but also in elasticity and plasticity. Based on destabilization of the solid state we have developed a series of metalloid-free Fe-based metallic glasses of composition (Fe0.582Co0.418)100−x−yCrxZry (10⩽x⩽28 and 8⩽y⩽11). Via this destabilization the liquid state is stabilized, which results in a decreasing liquidus temperature. The mechanical and magnetic properties of the metalloid-free Fe-based metallic glass with the highest Fe and Co fractions were analyzed. The alloy of composition (Fe0.582Co0.418)80Cr10Zr10 exhibits bending elasticity and plasticity. Magnetization measurements reveal a saturation magnetization of up to 1.1T and an inverted hysteresis. The origin of this inverted hysteresis presumably lies in the inclination to decompose in a ferromagnetic iron-rich α1 phase and an antiferromagnetic chromium-rich α2 phase.