Numerical study of hysteresis and morphology in elongated tape particles

A three-dimensional micromagnetic model with cubic discretization is used to examine switching field dependence on particle size, aspect ratio, external field angle, and shape morphology for typical tape particles. For rectangular particles, discretization along the particle axis gives accurate switching fields for all radii approximately less than an exchange length. Switching fields are independent of aspect ratio for 5:1 and greater rectangular particles except for sufficiently small radii where uniform switching occurs. Spherocylinders, cylinders, and rectangular parallelepipeds give virtually the same switching field at least for all radii less than two exchange lengths. For radii approximately equal to an exchange length, the corresponding switching field of an ellipsoid is nearly twice that of these other shapes. Numerical results for approximate ellipsoids agree with analytical predictions and previous fine element method calculations. (C) 1999 American Institute of Physics. [S0021-8979(99)66808-6].