  We formulate statistical mechanics for the mixed diamond chain with spins of
magnitudes 1 and 1/2. Owing to a series of conservation laws, any eigenstate of
this system is decomposed into eigenstates of finite odd-length spin-1 chains.
The ground state undergoes five quantum phase transitions with varying the
parameter $\lambda$ controlling frustration. We obtain the values of the
residual entropy and the Curie constant which characterize each phase and phase
boundary at low temperatures. We further find various characteristic
finite-temperature properties such as the nonmonotonic temperature dependence
of the magnetic susceptibility, the multipeak structure in the
$\lambda$-dependence of entropy, the plateau-like temperature dependence of
entropy and the multipeak structure of specific heat.

Strongly Correlated Electrons;Statistical Mechanics