Effect of magnetic field on the spin-Peierls transition in single-crystal CuGeO

This paper reports that high quality CuGeO_3 single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spin-Peierls (SP) transition temperature (T_\rm sp) under magnetic fields applying along both the a- and c-axis direction can be fitted well by a model of noninteracting dimmers. The spin gap derived from the fitting is consistent with other reports. There is a very weak anisotropy in the fitting parameters for different directions, which should be expected from a SP system. A small upturn in susceptibility at low temperature due to paramagnetic impurities and/or defects can be observed. A suppression of the upturn by magnetic field is first discovered in this system and the possible origins for this suppression are discussed.