We have studied the effect of magnetostatic interactions on the overall sha
pe of hysteresis loops for arrays of single domain particles, A computation
al model was used to calculate major hysteresis loops of arrays of particle
s with an easy axis along the applied field, The shear of the hysteresis lo
op, and consequent loss of squareness, is found to increase both with magne
tostatic 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 th
e plane. For cylindrical particles, we find an excellent fit between the mo
del and data. On the contrary, for flat ellipsoidal particles and evaporate
d conical particles, the fit to the measured loop was poor. This is believe
d to be due to the spread in easy axis directions or nonuniform reversal in
these particles.