Relationship between weak ferromagnetism, superconductivity, and lattice parameter in the A2−x−y&amp;gt;BxCeyCuO4 (<i>A</i>,<i>B</i>≡La, Pr, Nd, Sm, Eu, Gd, Y) compounds

Abstract

We report the results obtained by x-ray, dc magnetization, ac magnetic susceptibility, microwave magnetic absorption, and electron paramagnetic resonance of the magnetic and superconductive properties of a large series of compounds of the form A2−x−yBxCeyCuO4 with A,B≡La, Pr, Nd, Sm, Eu, Gd, and Y. For y=0 antiferromagnetic ordering of the copper moments is present at TN≊280 K for all the compounds formed in the tetragonal T′ phase. Weak ferromagnetism (WF) associated with the canting of the copper moments is observed in all the compounds with a lattice parameter, a&amp;lt;a0, a0≊3.91 Å, regardless of the rare-earth (R) ions present in the system. Superconductivity is observed only in the Ce-doped compounds with a≳a1, a1≊3.92 Å. The maximum onset temperature Tc is found for a≊3.95 Å. A phase diagram was obtained by varying the lattice parameter size as a function of A, B, and x. The correlation between the appearance of WF in the undoped compounds and the disappearance of superconductivity in the Ce-doped systems is discussed.