  This work reports on the magnetic reversal of sub-micrometer sized elements
consisting of an CoFeB/Ru/CoFeB artificial ferrimagnet (AFi). The elements were
patterned into ellipses having a width of approximately 250 to 270nm and a
varying aspect ratio between 1.3 and 8. The coercivity was found to decrease
with an increasing imbalance of the magnetic moment of the two
antiferromagnetically coupled layers and is therefore strongly affected by an
increase of effective anisotropy due to the antiferromagnetic coupling of the
two layers. With respect to a single layer of amorphous CoFeB, patterned in
comparable elements, the AFi has an increased coercivity. Switching asteroids
comparable to single layers were only observed for samples with a high net
moment.
