  Organometallic complexes formed by transition metals clusters and benzene
molecules have already been synthesized, and in selected cases display magnetic
properties controlled by external magnetic fields. We have studied Ni$_n$Bz$_n$
complexes made of nickel atoms surrounded by benzene molecules and here we
focus specifically on the magnetic molecule Ni$_{3}$Bz$_{3}$. By means of
calculations including relativistic spin-orbit terms, we show that this
molecule reveals a large magnetic anisotropy energy of approximately 8 meV,
found with the easy axis perpendicular to the metal atoms plane. Note that the
matching bare Ni$_{3}$ cluster have similar magnetic anisotropy, however the
easy axis is in-plane. Covering with benzene molecules is thus switching the
easy axis from in-plane for Ni$_3$ to out-of-plane for Ni$_{3}$Bz$_{3}$. The
large out-of-plane magnetic anisotropy of Ni$_{3}$Bz$_{3}$ suggests that this
molecule could indeed be used as part in the design of molecular magnetic
memories.
