Magnetic analog of the isotope effect in cuprates

Abstract

We present extensive magnetic measurements of the (Cax La1-x) (Ba1.75-x La0.25+x) Cu3 Oy system with its four different families (x) having a Tcmax (x) variation of 28% and minimal structural changes. For each family, we measured the Néel temperature, the anisotropies of the magnetic interactions, and the spin-glass temperature. Our results exhibit a universal relation Tc =cJ ns for all families, where c∼1, J is the in-plane Heisenberg exchange, and ns is the superconducting carrier density. This relates cuprate superconductivity to magnetism in the same sense that phonon-mediated superconductivity is related to atomic mass. © 2006 The American Physical Society.