We report the results of specific-heat measurements of ${\mathrm{CuGe}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{O}}_3$ (x=0, 0.01, 0.02) single crystals in magnetic fields up to 15 T. For x=0.02, a sharp transition was observed at the Néel temperature ${\mathrm{T}}_{\mathrm{N}}$=4.8 K, which is almost constant up to 15 T. For x=0.01, two broad transitions were observed at the spin-Peierls transition temperature ${\mathrm{T}}_{\mathrm{SP}}$=10.8 K and ${\mathrm{T}}_{\mathrm{N}}$=2.5 K in zero magnetic field. The antiferromagnetic state is changed drastically by the magnetic field and the magnetic-field-induced magnetic state was observed by specific-heat measurements. The magnetic phase diagram of ${\mathrm{CuGe}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{O}}_3$ was determined from specific-heat, thermal-expansion, and magnetization measurements.

DOI:https://doi.org/10.1103/PhysRevB.55.R6125