  Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains
are examined using quantum Monte Carlo simulations for two different quantum
spin numbers S = 1 and 3/2. The calculated magnetization curves at finite
temperatures are confronted with zero-temperature magnetization data obtained
within density-matrix renormalization group method, which imply an existence of
two quantum critical points determining a breakdown of the gapped Lieb-Mattis
ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively.
While a square-root behavior of the magnetization accompanying each quantum
critical point is gradually smoothed upon rising temperature, the
susceptibility and isothermal entropy change data provide a stronger evidence
of the quantum critical points at finite temperatures through marked local
maxima and minima, respectively.
