Spontaneous vortex phase in a superconducting weak ferromagnet

Abstract

In high-${T}_{c}$ superconducting compounds ${R}_{1.5}{\mathrm{Ce}}_{0.5}{\mathrm{RuSr}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10}$ the onset of superconductivity occurs at a temperature ${T}_{c}$ much lower than the temperature of the phase transition to weak ferromagnetism, and the diamagnetic response arises at the temperature ${T}_{d},$ which is much lower than ${T}_{c}.$ The present paper contains experimental data and a theoretical analysis of this phenomenon. These results collectively show convincingly that between ${T}_{c}$ and ${T}_{d}$ vortices are present in the sample in equilibrium without an external magnetic field (the spontaneous vortex phase).