MEASUREMENT AND UNDERSTANDING OF THE TEMPERATURE-DEPENDENCE OF THE LOWER CRITICAL-FIELD IN YNI2B2C

The lower critical field (H-c1(T)) values in YNi2B2C (T-c = 15.45 K) a re found to fit the quadratic form H-c1(T) = 220 [1-(T/T-c)(2)] Oe fro m 5 to 14 K. These values are consistent with an analysis which uses a thermodynamical critical field H-c(0) of 1.7 kOe (deduced from experi ments). However, measured values of H-c1(T) above 14.4 K deviate from the quadratic relation. Taking cue from the presence of intergranulari ty effects above 14.4 K in our YNi2B2C sample, the H-c1 data are quant itatively described in terms of a two-component magnetic response.