MAGNETIC AND STRUCTURAL-PROPERTIES OF FE IN SINGLE-CRYSTALS OF YBA2CU3-XFEXO7-DELTA

Magnetization and lattice-constant measurements were done on four single crystals of YBa2Cu(3-x)Fe(x)O7-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 Fe3+ with a magnitude of 2.18-mu-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.