| 摘要 |
PURPOSE:To increase an output regarding a high-density medium, and to improve a sealing effect and a lubrication effect as a magnetic fluid by holding high saturation magnetization, keeping the anisotropic constant of raw material particles within a predetermined range. CONSTITUTION:As the result of the measurement of a plurality of the samples of raw-material particles, it is distinct that particle size Dp extends over the region of small particle size with the increase of a crystallomagnetic anisotropic constant K1. When the saturation magnetization of sample particles is represented by sigmasemu/g and that of a bulk by sigmaoemu/g, standardized saturation magnetization sigmas/sigmao displays distinct K1 dependency in particle size such as 10nm one in ultrafine particles having a material having the larger constant K1, and ultrafine particles hav smaller particle size have high correlativity within a certain range. On the contrary, a material having large K1 has small particle-size dependency, and the lowering of sigmas can be suppressed. The constant K1 of particles is set within a range such as 2 X 10<5> - 10<7>erg/cm<2> one from the result of measurement, thus holding high saturation magnetization. |
