Orientation of Feeble Magnetic Particles in Dynamic Magnetic Fields

The motion of a feeble magnetic particle in a viscous medium subjected to dynamic magnetic fields including rotating and elliptic magnetic fields has been studied. Analysis of the differential equation describing the motion under a rotating field shows that in the synchronous rotation regime, the orientation of the hard magnetization axis in the z-direction becomes extremely slow when the frequency of the magnetic rotation is decreased. In a frequency-modulated elliptic magnetic field, which enables biaxial alignment, it is shown that the fluctuations of the two magnetic axes are not equalized for some sets of magnetic susceptibilities. (C) 2009 The Japan Society of Applied Physics