Study on CuGe0.9885Si0.0115 is O-3 in high magnetic fields by specific heat measurements

Specific heat is measured for a single crystal of CuGe1-xSixO3 (x = 0.0115) in magnetic fields up to 14.5 T. In zero field two peaks at similar to 3 a nd similar to 10 K were observed, suggesting that the coexistence of the an tiferromagnetic and spin-Peierls orders are realized. In our previous measu rements of specific heat in high-field region around 15 T a small but clear anomaly was observed at similar to 4.2 K for x = 0.01, while a sharp peak was observed at similar to 5 K for x = 0.015, which corresponds to the tran sition in the magnetic-field-induced phases between M phase and M' phase. T hey appear very different from each other. In the present study for x = 0.0 115 we observe a clear peak at 14.5 T which is just intermediate between th ose for x = 0.01 and 0.015 in temperature and in size. This systematic chan ge in the transition with varying x shows that these transitions in the hig h-field phases are of the same kind in this range of x, though it also show s that small change in Si concentration affects the magnetic-field-induced states to a large extent. (C) 2000 Elsevier Science B.V. All rights reserve d.