Anomalous Magnetization Central Peak Shift of Nb-Ti Tapes with High In-Plane Critical Current Anisotropy

Magnetization curves measured with the Vibrating-Sample Magnetometer (VSM) are presented for narrow (2 x 11 mm typical) rectangular samples sliced from superconducting Nb-Ti cold-rolled tape with high pinning anisotropy. There are two types of samples: sliced along (RD) and across (TD) to the rolling direction. An anomalous shift of the magnetization central peak was found for TD-samples and not observed for RD-samples. This central peak shift is opposite in sign to the known one, which is usually observed in bulk materials. The Magneto-Optical Imaging (MOI) pictures suggest a possible mechanism for such an anomalous shift. From the longitudinal side, the magnetic flux penetrates into the tape relatively evenly, in accordance with the predictions of the critical state model. However, it is not true for flux penetration from the transverse side of the sample. Instead, the flux forms a dendritic structure oriented primarily along the rolling direction. The existence of such a structure leads to a drastic change in total magnetization around zero external fields, depending on the orientation of the rolling direction to the long side of the sample.

Automated summary

Magnetization curves of narrow rectangular samples from superconducting Nb-Ti cold-rolled tape were measured using a Vibrating-Sample Magnetometer (VSM). Two types of samples, sliced along and across the rolling direction, were analyzed. An anomalous shift of the magnetization central peak was observed only in the samples sliced across the rolling direction, which is opposite to the usual shift observed in bulk materials. Magneto-Optical Imaging (MOI) pictures provide a possible mechanism for this anomalous shift, showing a dendritic structure of magnetic flux penetrating from the transverse side of the sample.