THE SPIN-1/2 HEISENBERG-STAR WITH FRUSTRATION - GROUND-STATE AND THERMODYNAMICS

We investigate a spin 1/2 Heisenberg antiferromagnet (AFM) H = J(1) Sigma(i=1)(N) s(0)s(i) + J(2)H(R){s(i)} descibing a central spin which interacts with a surrounding medium H-R. We present general relations for the eigen values, the eigen dates and the spin correlation function and study the model an more detail for H-R Being either a linear chain or a Lieb-Mattis AFM. Additional do the ground state properties we calculate the full thermodynamics in the case of H-R being a Lieb-Mattis AFM. PACS-Numbers: 75.10Jm, 75.50Ee, 05.50+q