Construction of hysteresis loops of single domain elements and coupled permalloy ring arrays by magnetic force microscopy

Magnetic structure and magnetization reversal of permalloy ring arrays and elongated permalloy particle array were studied by magnetic force microscopy (MFM). For single domain permalloy particles, the hysteresis loop is constructed by counting the percentage of switched elements imaged at remanence. For permalloy ring elements, two different states are energetically stable: a vortex state and an onion state. Their hysteresis loop is obtained by MFM imaging at a field between the switching fields of these two states. The magnetostatic coupling among these ring elements is directly revealed.