Off-axis electron holography of patterned magnetic nanostructures

Magnetization reversal processes in lithographically patterned magnetic ele ments that have lateral dimensions of 70-500 nm, thicknesses of 3-30 nm and a wide range of shapes and layer sequences have been followed in situ usin g off-axis electron holography in the transmission electron microscope. Thi s technique allows domain structures within individual elements and the mag netic interactions between them to be quantified at close to the nanometre scale. The behaviour of 30 nm-thick Co elements was compared with that of 1 0 nm-thick Ni and Co elements, as well as with Co/Au/Ni trilayers. The hyst eresis loops of individual elements were determined directly from the measu red holographic phase images. The reproducibility of an element's domain st ructure in successive cycles was found to be affected by the out-of-plane c omponent of the applied magnetic field and by the exact details of its init ial magnetic state. Close proximity to adjacent elements led to strong inte rcell coupling, and remanent states with the in-plane magnetic field remove d included domain structures such as solenoidal (vortex) states that were n ever observed during hysteresis cycling. Narrow rectangular bars reversed w ithout the formation of end domains, whereas closely separated magnetic lay ers within individual elements were observed to couple to each other during field reversal.