Magnetic Alignment of Magnetically Biaxial Diamagnetic Rods under Rotating Magnetic Fields

摘要

The alignment behavior of magnetically biaxial diamagnetic rods under rotating magnetic fields is studied to elucidate the effects of particle shape and rotation speed on alignment manner. Three types of rod (ca. 1.1 mmφ × 3 mm) are prepared: (ⅰ) rod axes parallel to x_1, (ⅱ) parallel to x_2. and (ⅲ) parallel to x_3, where xs are the principal axes of the diamagnetic susceptibility tensor and x_1 > x_2 > x_3- The motion of the rod is recorded on video and the angles required for the comparison with simulation are measured. Simulation is performed by numerically solving a torque equation including magnetic and hydrodynamic torques. The experimental results show a good agreement with simulation results. It is shown that the x_3-axis of rod sample (ⅱ) does not align parallel to the axis of the rotating magnetic field under most experimental conditions; this is in marked contrast to the case with magnetically uniaxial particles (x_1 = x_2 > x_3), for which the x_33-axis aligns irrespective of particle shape and/or rotation speed. This observation is interpreted in terms of magnetic energy and orientation kinetics.