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Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are calculated with the help of density-matrix renormalization group method for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown that the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective of the spin value S exactly one intermediate magnetization plateau, which can be identified with the gapped Lieb-Mattis ferrimagnetic ground state. The magnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at a quantum phase transition towards the Luttinger spin liquid, which is characterized by a continuous change of the magnetization with the magnetic field until another quantum critical point is reached at the saturation field. [ABSTRACT FROM AUTHOR]

The effect of uniaxial single-ion anisotropy on magnetic and critical properties of the mixed spin-1/2 and spin- S (S > 1=2) Ising model on a three-coordinated Bethe lattice is rigorously examined with the help of star-triangle transformation and exact recursion relations. In particular, our attention is focused on the ferrimagnetic version of the model, which exhibits diverse temperature dependences of the total and both sublattice magnetizations. It is shown that the critical behavior of the mixed-spin Ising model on the Bethe lattice basically depends on whether the quantum spin number S is integer or half-odd-integer. [ABSTRACT FROM AUTHOR]

The Green function theory is used to study the phenomenon of magnetic reorientation in the ferrimagnetic system. The two-sublattice ferrimagnetic system, with different spins and the intra-sublattice ferromagnetic exchange interactions, is considered. The magnon fluctuations supress in different way the magnetic orders of the sublattices and one obtains two magnetic orders. Each of these orders has different reorientation temperatures. [ABSTRACT FROM AUTHOR]