Arrays of evaporated nickel particles with a variety of diameters (75-122 nm) and aspect ratios are fabricated in order to study the effect of the particles' geometry on their magnetic behavior, interactions and switching mechanism. Hysteresis loops generated by simulating single-domain particles with out-of-plane magnetization are compared to the experimentally obtained data. (C) 2000 American Institute of Physics. [S0021-8979(00)37508-9].