Magnetic force microscopy studies of submicron and nanoscale magnet arrays

Magnetic structure and magnetization reversal of lithographically patterned submicron and nanometer scaled magnets with elliptical, disk, ring shapes, and pseudo spin valve structures, were studied by magnetic force microscopy.; Magnetic measurements were performed with a custom built vacuum magnetic force microscopy with in-situ in plane magnetic fields. The MFM has been optimized with a force gradient sensitivity as high as 1 × 10−6 N/m.; By using various magnetic tips, operating in different modes, and studying different samples, the effect of the magnetic tip stray field induced distortion of the magnetic state of a submicron sized magnet is presented. Through the systematic study, a method of how to detect and to avoid these irreversible distortions is also presented. A local ‘hysteresis loop’ technique has been invented to study the abrupt switching behavior of individual elements.; In arrays of elongated magnetic particle array, the aspect ratio dependence of the switching indicates that the vortex state can be trapped inside the elements and form an energetic stable state, leading to a broad switching field distribution. In an array of 70 nm wide pseudo spin valve elements, parallel and antiparallel single domain configurations are found. Major and minor hysteresis loops as well as inter-layer coupling are investigated. We found that interlayer coupling leads to switching field variations. In a Permalloy disk array, the vortex state with vortex core singularity is found. The switching mechanism through the nucleation and annihilation processes is demonstrated by the local hysteresis loop. An interdot coupling-induced anisotropic switching is observed. In Permalloy ring structures, a vortex state and an ‘onion’ state are found. The onion state in permalloy rings with diameters of 5μm is found to be a flux closure state with a head to head domain wall. The switching behavior of these ring elements is found to be domain wall propagation.