Magnetic characterization of bacterial magnetic particles

The experimental results on Mössbauer measurement, chemical analysis (a ratio of Fe²⁺ to total Fe content), analyses of the rotational hysteresis loss (Wr) and the measurement of magnetic viscosity coefficient (Sv) for bacterial magnetic particles (BMP, particle diameter D=25-65 nm) were compared with those of Fe₃O₄ particles (D=18-45 nm) prepared by the chemical coprecipitated method. The value of saturation magnetization (Js) calculated from Mössbauer spectrum and the results of chemical analysis for BMP was 1.06×10^-4 Wb m/kg. The curves of Wr/Ms versus H for BMP showed more sharp peaks than those of Fe₃O₄ particles. The rotational hysteresis integral (Rh) of BMP and Fe₃O₄ particles were 1.12 and 0.62, respectively. It was considered that they have different magnetization reversal mechanism. Sv value of BMP was 127 A/m, which was 50% smaller than that of Fe₃O₄ particles. The diameter (Dact) of activation volume (minimum unit volume of magnetization reversal) calculated from Sv and the critical diameter (Dc) obtained by considering the superparamagnetic behavior of BMP, were 39 and 22 nm, respectively. On the other hand, Fe₃O₄ particles had smaller Dact (31 nm) and Dc (18 nm). It may be concluded that the magnetic stability of BMP is better than that of Fe₃O₄ particles.