Nonlinear magnetization of niobium near Hc2

Abstract

In a previous paper we reported the measurements of both C/T and đQ/dH of high-purity niobium as functions of the applied field at a number of chosen temperatures. In the present paper we analyze the slopes of these “magnetocaloric” quantities in the reversible region near H_c2. These slopes are related to the nonlinearity of the magnetization curve by means of a third-order field term in the Gibbs free energy. At the chosen temperatures the small values of the coefficient of this field term are calculated and found to be in agreement with the model of the reversible magnetization curve proposed by Kes.