  We study the phase diagram of a symmetric spin-1/2 Heisenberg diamond chain
with additional cyclic four-spin exchange interactions. The presented analysis
supplemented by numerical exact-diagonalization results for finite periodic
clusters implies a rich phase diagram containing, apart from standard magnetic
and spin-liquid phases, two different tetramer-dimer phases as well as an
exotic four-fold degenerate dimerized phase. The characteristics of the
established spin phases as well as the nature of quantum phase transitions are
discussed, as well.
