Single particles and particle arrays are investigated by numerical simulation and by the fabrication and characterization of nearly ideal samples prepared by nanolithography. Hysteresis and particle interactions are modeled analytically and compared to the experimental data. Intergranular interactions in thin films and their contributions to recording noise are analyzed by computer modeling. Micromagnetic analyses are applied to the single and multilayer thin films currently used for magnetoresistive read heads. Micromagnetic calculations are also used to predict the optimum properties required for future ultra-high density media.