Magnetic ordering of high-Tc superconducting systems studied by Mossbauer spectroscopy

Abstract

This review article is concerned with the interrelation between the phenomena of superconductivity and antiferromagnetic order in high-Tc superconductors. Magnetometry, Mossbauer spectroscopy and X-ray diffraction, have been utilized to study the R2CuO4, RBa2Cu3O7, RBa2Cu4O8, Bi2Sr2CaCu2O8 and La2(Ca,Sr)Cu2O8 systems in their pure form as well as in a wide variety of substituted systems. For each compound, Tc was determined by magnetometry and Tn of the Cu sublattice by Mossbauer spectroscopy of a dilute 57Fe probe. Full superconductivity-antiferromagnetism phase diagrams were established. All high-Tc superconductor compounds have a layered structure with CuO2 planes which are responsible for superconductivity. It is shown here that in all systems studied, whenever substitution of cations is made outside these CuO2 planes in an amount sufficient to make superconductivity disappear, static long-range antiferromagnetism is induced in these planes. On the other hand substitution of Cu in the sites responsible for superconductivity even by non-magnetic ions, suppresses both superconductivity and magnetic order. It is thus concluded that in the investigated high-Tc systems, superconductivity and antiferromagnetism are closely related, they compete with each other and rarely coexist. Moreover, in all cases Tn obtained in the antiferromagnetic branch is directly proportional to Tc observed in the superconducting branch of the phase diagram. The close relationship between the two physical phenomena suggest a new guideline in searching for new high-Tc superconductor materials.