TWO-DIMENSIONAL ANTIFERROMAGNETIC ORDERING IN HIGH-Tc SUPERCONDUCTORS WITH LOW OXYGEN CONTENT

Abstract

Since the discovery of superconductivity in the temperature range of 90-93 K in YBa{sub 2}Cu{sub 3}O{sub 7 {minus} {delta}}, which is the so-called 123 compound, much effort has been devoted to assess copper cation state (valence and spin value) and their distribution among Cu(1) and Cu(2) planes. Understanding this is of considerable importance since copper electrons form the conduction band. Moreover, understanding plane distribution of copper ions allows to ascertain the copper plane (Cu(1) or Cu(2)) which is responsible for superconductivity. Copper ions have been found to be in three different electronic configurations in this compound: 3d{sup 10}, 3d{sub 9}, 3d{sup 8} (Cu{sup 1+}, Cu{sup 2+}, Cu{sup 3+}). Obviously, their correlation and, possibly, distribution among different planes may be changed depending on the oxygen content. The presence of 3d-cations, which bear nonzero spin magnetic moment, may lead to magnetic ordering by analogy with well-known perovskites. Antiferromagnetic order of the copper sublattice (Cu(2)-plane) has been observed by neutron scattering for low oxygen content samples of YBa{sub 2}Cu{sub 3}O{sub 7 {minus} {delta}}. Therefore, investigation of copper ion states and their distribution among different planes with varying oxygen content excites interest. Mosssbauer spectroscopy of {sup 57}Fe atoms doped YBa{sub 2}Cu{sub 3}O{sub 7 {minus}more » {delta}} compound makes it possible to investigate electronic properties, crystallographic positions of ions, and moreover, magnetic order. The present paper aims to obtain measurements of {sup 57}Fe Mossbauer isotope incorporated into the superconductor in order to determine the copper ions states, their distribution among Cu(1) and Cu(2) planes as well as magnetic order in oxygen deficient samples.« less