MAGNETIC ORDER IN 2-DIMENSIONAL ARRAYS OF NANOMETER-SIZED SUPERPARAMAGNETS

Random two-dimensional island assemblies have three magnetic phases at room temperature as a function of island radius a. These magnetic sta tes are a perpendicularly magnetized random antiferromagnet (a < 1.5 n m), an in-plane superparamagnet (1.5 < a < 3 nm), and an in-plane ferr omagnet (a > 3.0 nm) in a superferromagnetic regime. Mean-field and Mo nte Carlo methods are used to examine order-disorder transitions in tw o dimensions, and to set minimum interisland coupling strengths.