  A study of the multilayer system MgO/CoFeB(1.1nm)/Ta($t$)/CoFeB(0.8nm)/MgO is
presented, where the two CoFeB layers are separated by a Ta interlayer of
varying thickness $t$. The magnetization properties deduced from complementary
techniques such as superconducting quantum interference magnetometry,
ferromagnetic resonance frequency measurements and Brillouin light scattering
spectroscopy can be tuned by changing the Ta thickness between $t$=0.25 nm, 0.5
nm and 0.75 nm. For $t$=0.5 nm, a ferromagnetic coupling is observed, whereas
for t=0.75 nm, the antiferromagnetic coupling needed to construct a synthetic
ferrimagnet is realized. In the later case, the shape of magnetic domain walls
between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic
alignment is very different. This behavior can be interpreted as a result of
the change in dipolar as well as interlayer exchange energy and domain wall
pinning, which is an important conclusion for the realization of data storage
devices based on synthetic ferri- and antiferromagnets.
