Major hysteresis loop modeling of two-dimensional arrays of single domain particles

We have studied the effect of magnetostatic interactions on the overall shape of hysteresis loops for arrays of single domain particles. A computational model was used to calculate major hysteresis loops of arrays of particles with an easy axis along the applied field. The shear of the hysteresis loop, and consequent loss of squareness, is found to increase both with magnetostatic interaction strength and with the standard deviation of switching field for the particles. This model has been tested with several shapes of particles, including arrays with easy axes parallel and perpendicular to the plane. For cylindrical particles, we find an excellent fit between the model and data. On the contrary, for flat ellipsoidal particles and evaporated conical particles, the fit to the measured loop was poor. This is believed to be due to the spread in easy axis directions or nonuniform reversal in these particles.