VIRTUAL ADDITIVE MOMENTS MEASURED BY A VIBRATING SAMPLE MAGNETOMETER ON SUPERCONDUCTING THIN-FILMS

Virtual additive magnetic moment was observed on a series of YBaCuO th in films in an external field perpendicular to the film plane: magneti c hysteresis loops measured by a PAR 155 vibrating sample magnetometer up to fields of +/-2 T were symmetrical at high field sweep rates, wh ereas at;ow sweep rates they exhibited a large additive offset of the reversible magnetic moment, This effect increased particularly at high fields and it was especially noticeable at intermediate temperatures, typically between 40 and 65 K. We identified this phenomenon as an ar tefact originating from vibrations of a sample possessing a high diffe rential susceptibility in a slightly inhomogeneous bias field, This un desirable effect is quite general and it can be generated in any type of VSM with even very slight inhomogeneity of magnetic field. it can h owever, be found only on laterally large, thin samples with a high dif ferential susceptibility (typically thin films). Experimental results are consistently explained by the proposed model, We present expressio ns which enable us to estimate this effect from the differential susce ptibility of the sample and known inhomogeneity of the bias magnetic f ield.