"Intermediate Mixed" State of Type-II Superconductors

Abstract

For magnetic fields in the range $(1\ensuremath{-}D){H}_{c1}<H<{H}_{t}$, magnetization curves of low-$\ensuremath{\kappa}$ type-II Pb-In and In-Bi alloys with nonzero demagnetization coefficients $D$ exhibit a linear dependence of the magnetic moment on applied field. ${H}_{c1}$ is the lower critical field and ${H}_{t}$ is the field at which this linear dependence terminates. For finite $D$, ${H}_{t}<{H}_{c1}$. This behavior can be explained by a model of alternate regions of superconducting and mixed states. This array may be metastable. The mixed-state regions are all presumed to have the same temperature-dependent fluxoid-lattice spacing characteristic of ${H}_{c1}$ when $D=0$. Thus, as the magnetic field is increased isothermally, the mixed-state regions grow until the whole sample has been converted into the mixed state. This model implies the existence of an attractive interaction between flux lines in low-$\ensuremath{\kappa}$ materials.