Magnetization reversal of patterned spin-tunnel junction material: A transmission electron microscopy study

Electron beam lithography and reactive ion etching have been used to patter n micron-size magnetic elements in the free layer of spin-tunnel junctions. The magnetization reversal processes of elements with dimensions in the ra nge from 15x1 mu m(2) to 1x1 mu m(2) have been studied using Lorentz micros copy in the transmission electron microscope. Under the application of a fi eld parallel to the bias direction, elongated elements reverse by the growt h and subsequent annihilation of a quasiperiodic domain structure which evo lves from the ends of the elements. Similar processes occur in both halves of a magnetization cycle. By contrast, the reversal of square elements invo lves the formation of more complex domain structures which differ significa ntly according to the direction in which the field in applied. (C) 2000 Ame rican Institute of Physics. [S0021-8979(00)04817-9].