Precursor diamagnetism above the superconducting transition in YNi $_\mathsf{2}$ B $_\mathsf{2}$ C

High-resolution SQUID magnetization measurements in a single crystal of YNi 2 B 2 C around the superconducting transition are reported. The diamagnetic magnetization -M fl at constant field H as a function of temperature and isothermal magnetization curves -M fl vs. H are used to derive insights on precursor phenomena approaching the bulk transition temperature $T_c(H=0)=15.25\pm0.02$ K. The precursor diamagnetism is found strongly enhanced with respect to the conventional Ginzburg-Landau value for Gaussian fluctuations and the curves -M fl vs. H exhibit an upturn with the field and hysteretic effects up to T * =15.4 K. These results are interpreted in terms of a non-zero order parameter in superconducting droplets above the bulk T c . These droplets are likely to be related to inhomogeneities resulting from small amount of boron to carbon substitutions. Copyright Springer-Verlag Berlin/Heidelberg 2003