  We study an integrable spin chain with an alternating array of spins S=1/2, 1
in external magnetic fields using the Bethe ansatz exact solution. The
calculated magnetization possesses a cusp structure at a critical magnetic
field H=H_{C}, at which the specific heat shows a divergence property. We also
calculate finite-size corrections to the energy spectrum, and obtain the
critical exponents of correlation functions with the use of conformal field
theory (CFT). Low-energy properties of the model are described by two c=1 U(1)
CFTs in H<H_{C} and one c=1 U(1) CFT in H>H_{C}.
