MAGNETIC-ORDERING OF HIGH-T-C SUPERCONDUCTING SYSTEMS STUDIED BY MOSSBAUER-SPECTROSCOPY

This review article is concerned with the interrelation between the ph enomena of superconductivity and antiferromagnetic order in high-T-C s uperconductors. Magnetometry, Mossbauer spectroscopy and x-ray diffrac tion, have been utilized to study the R(2)CUO(4), RBa(2)CU(3)O(7), RBa (2)CU(4)O(8), Bi2Sr2CaCu2O8 and La-2(Ca, Sr)Cu2O6 systems in their pur e form as well as in a wide variety of substituted systems. For each c ompound, T-c was determined by magnetometry and T-n of the Cu sublatti ce by Mossbauer spectroscopy of a dilute Fe-57 probe. Full superconduc tivity-antiferromagnetism phase diagrams were established. All high-T- C superconductor compounds have a layered structure with CuO2 planes w hich are responsible for superconductivity. It is shown here that in a ll systems studied, whenever substitution of cations is made outside t hese CuO2 planes in an amount sufficient to make superconductivity dis appear, static long-range antiferromagnetism is induced in these plane s. On the other hand substitution of Cu in the sites responsible for s uperconductivity even by non-magnetic ions, suppresses both supercondu ctivity and magnetic order. It is thus concluded that in the investiga ted high-T-c systems, superconductivity and antiferromagnetism are clo sely related, they compete with each other and rarely coexist. Moreove r, in all cases T-n obtained in the antiferromagnetic branch is direct ly proportional to T-c observed in the superconducting branch of the p hase diagram. The close relationship between the two physical phenomen a suggest a new guideline in searching for new high-T-c superconductor materials.