Title: ON THE FUNCTIONAL REPRESENTATION OF PARTITION FUNCTION FOR QUANTUM MAGNETIC CLUSTER SYSTEMS
Author(s): N.A.Korynevskii (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine; Institute of Physics, University of Szczecin, 15 Wielkopolska Str., 70451 Szczecin, Poland)

The problem of the functional representation for systems containing groups of atoms with a non-compensated spin momentum (magnetic clusters) is discussed. For representation of the functional of partition function a version of the collective variables method with the ``reference system'' as a zero-order approximation is used. A set of all isolated clusters are choosen as a reference system. Intracluster interactions are described by exchange Heisenberg-type Hamiltonian, the form of intercluster interactions depend on the structure of the system investigated. Due to the use of the recently introduced generalized transition operators (like well-known Hubbard-Stasyuk operators) an explicit form of the functional of partition function is found.

Key words: cluster system, functional of partition function, reference system
PACS: 05.60.+W, 05.70.Ln, 05.20.Dd, 52.25.Dg, 52.25.Fi