  The magnetization process of the spin-1 Heisenberg dimer model with axial and
rhombic single-ion anisotropy terms is particularly investigated in connection
with recent experimental high-field measurements performed on the
single-crystal sample of the homodinuclear nickel(II) compound
[Ni2(Medpt)2(ox)(H2O)2](ClO4)2.2H2O (Medpt=methyl-bis(3-aminopropyl)amine). The
results obtained from the exact numerical diagonalization reveal a striking
magnetization process with a marked spatial dependence on the applied magnetic
field for arbitrary but non-zero single-ion anisotropy. It is demonstrated that
the field range, which corresponds to an intermediate magnetization plateau
emerging at a half of the saturation magnetization, basically depends on
single-ion anisotropy terms as well as a spatial orientation of the applied
field. The breakdown of the intermediate magnetization plateau is discussed at
length in relation to the single-ion anisotropy strength.
