Surface superconductivity, positive field cooled magnetization, and peak-effect phenomenon observed in a spherical single crystal of niobium

Abstract

We report the observation of surface superconductivity as well as positive field cooled magnetization, along with peak-effect phenomenon in ac and dc magnetization measurements in a high-purity spherical single crystal of niobium. We study how the surface superconductivity and the positive field cooled magnetization evolve over the field $(H)$ and the temperature $(T)$ phase space. We suggest that the observed evolution in the strength of the positive field cooled magnetization signal may be understood on the basis of the temperature dependence of the superconducting coherence length.