J. Phys. IV France 07 (1997) C1-663-C1-666
Magnetic Characterization of Bacterial Magnetic ParticlesH. Nishio1, T. Takahashi1, H. Taguchi1, S. Kamiya2 and T. Matsunaga3
1 Materials Research Center, TDK Corporation, 570-2, Aza-Matsugashita, Minami-Hatori, Narita 286, Japan
2 TDK Akita Laboratory Corporation, 15 Aza-Gashomen, Hirasawa, Nikaho-machi, Yuri-gun, Akita 018-04, Japan
3 Tokyo University of Agriculture and Technology, 2-24-16, Nakamachi, Koganei 184, Japan
Mössbauer measurement, chemical analysis (ratio of Fe2+ 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 Fe3O4 fine particles prepared by a chemical coprecipitation method. The calculated value of the saturation magnetization (Js) of BMPs was found to be 1.06 X 10-4 Wb m/kg (84.7 emu/g) using Mössbauer spectroscopy and chemical analysis. The Wr/Js versus H curve for BMPs had a stronger peak than that of Fe3O4 fine particles (Sample Cl). The rotational hysteresis integrals (Rh) for BMPs and Fe3O4 fine particles 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 Fe3O4 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 Fe3O4 fine particles (C1) have smaller Dact(31 nm) and Dc(18 nm), it may be concluded that BMPs is magnetically more stable than Fe3O4 fine particles (C1).
© EDP Sciences 1997