Low-temperature properties of a mixed spin Heisenberg ferrimagnetic system on a honeycomb lattice

The low-temperature properties of a mixed spin-2 and spin-5/2 Heisenberg ferrimagnetic system on a honeycomb lattice are studied using a linear spin-wave theory. The magnetizations and the internal energy at zero and low temperature, the spin-wave spectrum, and the specific heat are calculated. The effects of the interlayer interaction and the anisotropy are discussed. It is found that the spin-wave spectrum breaks into two optical branches from the effects of the anisotropy and there is no expected acoustical branch when there is single-ion anisotropy. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.