Inferring equilibrium magnetization from hysteretic M-H curves of type-II superconductors

Abstract

Isothermal M-H curves, coupled with the critical state model, are routinely used to extract critical current density J_c(B); and the limitations and validity are well understood. These hysteretic M-H curves can also be used to estimate the equilibrium magnetization M_eq(H), and this paper discusses the validity of such a procedure using analytically tractable models for J_c(H). We put special emphasis on the case where the M-H curve shows a fish tail or peak effect, and an experimental procedure to estimate errors in the inferred M_eq(H) is presented. The need to infer M_eq(H) is underscored by recent experimental works speculating on thermodynamic phase transitions between vortex phases having intrinsic pinning.