Abstract
Mossbauer measurement, chemical analysis (ratio of Fe 2+ to total Fe content), analyses of the rotational hysteresis loss (Wr) and the magnetic viscosity coefficient (Sv) for bacterial magnetic particles covered with organic thin films (BMPs) were investigated and compared with the results for Fe 3 O 4 fine particles prepared by a chemical coprecipitation method. The calculated value of the saturation magnetization (Js) of BMPs was found to be 1.06x10.4 Wb m/kg (84.7 emu/g) using Mossbauer spectroscopy and chemical analysis. The Wr/Js versus H curve for BMPs had a stronger peak than that of Fe 3 O 4 fine particles (Sample C1). The rotational hysteresis integrals (Rh) for BMPs and Fe 3 O 4 fineparticles were 1.12 and 0.62, respectively. It is believed that they have different magnetization reversal mechanisms. The Sv value of BMPs at 127A/m was 50% smaller than that of the Fe 3 O 4 fine particles (C1). The diameter (Dact) of the activation volume (minimum volume for magnetization reversal) calculated from Sv, and the critical diameter (Dc) obtained by considering the superparamagnetic behavior for BMPs, were 39 and 22 nm, respectively. As the Fe 3 O 4 fine particles (C1) have smallerDact(31 nm) and Dc(18 nm), it may be concluded that BMPs is magnetically more stable than Fe 3 O 4 fine particles (C1).
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