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Magnetization non-rational quasi-plateau and spatially modulated spin order in the model of the single-chain magnet, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O

Using the exact solution in terms of the generalized classical transfer matrix method we presented a detailed analysis of the magnetic properties and ground state structure of the simplified model of the single-chain magnet, trimetallic coordination polymer compound, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O is N,N'-propylenebis(3-methoxysalicylideneiminato). Due to appearance of highly anisotropic Dy3+ ion this material is an unique example of the one-dimensional magnets with Ising and Heisenberg bonds, allowing exact statistical-mechanical treatment. We found two zero-temperature ground states corresponding to different part of the magnetization curve of the material. The zero-filed ground state is shown to be an antiferromagnetic configuration with spatial modulation of the local Dy3+(which is proven to posses well defined Ising like properties due two large anisotropy of g-factors) and composite S=1/2 spin of the quantum spin trimer Cu-Mo-Cu in the form "up"-"down"-"down"-"up". Another important feature of this compound is the appearance of the quasi-plateau at non rational value of magnetization due to difference of the g-factors of the Cu- and Mo-ion in quantum spin trimers. The quasi-plateau is an almost horizontal part of the magnetization curve where the corresponding zero-temperature ground state of the chain demonstrate slow but monotonous dependence of the magnetization on the external magnetic field, while the $z$-projection of the total spin is constant.