  A symmetric spin-1/2 Ising-Heisenberg diamond chain with the Ising four-spin
interaction is exactly solved by means of the generalized decoration-iteration
mapping transformation. The ground state, the magnetization process and
thermodynamics are particularly examined for the case of antiferromagnetic pair
interactions (Ising and isotropic Heisenberg ones). It is shown that an
interplay between pair interactions, the four-spin interaction and the external
magnetic field gives rise to several quantum ground states with entangled spin
states in addition to some semi-classically ordered ones. Besides, the
temperature dependence of the magnetic susceptibility multiplied by the
temperature is studied and the interesting triple-peak specific heat curve is
also detected when considering the zero-field region rather close to the triple
point, where three different ground states coexist.
