Magnetic field influence on the low temperature heat capacity of the spin-Peierls compound CuGeO3

We have investigated the effect of magnetic field on the low-temperature heat capacity Cp of the undoped spin-Peierls inorganic compound CuGeO3 in the dimerized phase. Below 1 K, Cp is dominated by a Schottky anomaly, which is removed above 1 K for field B higher than 3 T. This anomaly is well accounted for by a molar concentration x=0.75×10−3 of intrinsic defects, which occur predominantly on the Cu chains. This amount is confirmed by magnetization measurements. A second contribution, varying as T−ν with ν=1 or 2, rises up with the field for B>1 T in the lower temperature range (from 70 mK to 0.3 K). At high field this contribution becomes very sensitive to the experimental dynamics.