OBSERVATION OF UNUSUAL METASTABLE MAGNETIZATION IN THE SUPERCONDUCTING STATE OF NEARLY SINGLE-PHASED YNI2B2C AND ERNI2B2C

We report an unusual magnetization behavior observed by DC susceptibil ity measurements in the superconducting state of YNi2B2C and ErNi2B2C compounds after relatively fast cooling in zero or in magnet-remanent field. The magnetization of both substances exhibited an incomplete fl ux expulsion and evolved with time towards a stronger diamagnetic stat e. The time needed to reach a saturated value increased with the field and for H = 1 kOe the relaxation process lasted over decades of minut es. The saturated susceptibility value differed from that of the full shielding and the discrepancy increased with the field. The susceptibi lity observed was composed of a stable nondissipative diamagnetic part and of a decaying contribution of a positive sign. A simple thermal p rocedure could destroy the positive moment. This unusual magnetization behavior may be attributed to the enhanced magnetic granularity comin g from a small amount of nonsuperconducting secondary phase present in the samples or to the glassy state of spontaneous orbital moments con nected with pi junctions.