Magnetic and structural properties of Fe in single crystals ofYBa2Cu3−xFexO7−δ

Magnetization and lattice-constant measurements were done on four single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with Fe concentrations of x=0.06, 0.09, 0.15, and 0.24 to determine the structural and normal-state properties. Measurements of magnetization as a function of temperature were done in a temperature range between 90 and 300 K and analyzed using a Curie-Weiss law with a temperature-independent background. The effective magnetic moment obtained corresponds to a low spin state of ${\mathrm{Fe}}^{3+}$ with a magnitude of 2.18${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. Magnetic anisotropy between the ab plane and the c direction is only present for the concentration of x=0.06 and is attributed to the various oxygen environments surrounding the iron. For concentrations larger than x=0.06, the moment on Fe is isotropic and Curie-Weiss fits predict uniform antiferromagnetic ordering. Structural measurements exhibit an orthorhombic-tetragonal transition at an Fe concentration of x=0.15, similar to that observed in the polycrystalline material.