Observation of switching of magnetic particle arrays with weak dipole interaction field effects

We have measured the subtle changes in magnetic reversal of weakly interacting arrays of submicrometer magnetic particles as a function of particle spacing and interpreted the data within the context of a model assuming a normal distribution of switching fields plus dipole fields between particles. The measurements were performed on a Kerr magnetometer and showed the changes in switching characteristics of the particle array as a function of array spacing in the two in-plane directions. The Monte Carlo calculations included the effect of changing particle pitch in two in-plane directions and explained the characteristic change in sharpness of the switching transition alternatively as a frustration or as an enhanced sharpness due to cascading transitions, depending on whether the hard- or easy-axis dipole coupling is dominant. This method is extensible to nanoscale particles and provides an estimate of the moment of the particle, a measurement which is difficult to obtain via other experimental methods.