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

This paper reports that high quality CuGeOspin chain, spin--Peierls transition, spin dimmer, magnetic susceptibilityProject supported by the National Natural Science Foundation of China (Grant No 10634030) and the Zhejiang Province Natural Science Foundation of China (Grant No Y605106).7530F, 7530E, 7510J1/3/2008 12:00:00 AM2/5/2008 12:00:00 AMThis paper reports that high quality CuGeOspin chain, spin--Peierls transition, spin dimmer, magnetic susceptibilityProject supported by the National Natural Science Foundation of China (Grant No 10634030) and the Zhejiang Province Natural Science Foundation of China (Grant No Y605106).7530F, 7530E, 7510J1/3/2008 12:00:00 AM2/5/2008 12:00:00 AMThis paper reports that high quality CuGeOspin chain, spin--Peierls transition, spin dimmer, magnetic susceptibilityProject supported by the National Natural Science Foundation of China (Grant No 10634030) and the Zhejiang Province Natural Science Foundation of China (Grant No Y605106).7530F, 7530E, 7510J1/3/2008 12:00:00 AM2/5/2008 12:00:00 AMThis 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.