SUPERCONDUCTIVITY AND MAGNETIC ORDER IN THE CU(2) PLANES IN FE-DOPED YBA2CU4O8

Mossbauer spectroscopy, magnetic susceptibility, and powder x-ray-diffraction measurements were used to study superconductivity and magnetic order in YBa2(Cu(1-x)Fe(x))4O8+sigma. T(c) is reduced with increasing Fe concentration and superconductivity is totally depressed for x greater-than-or-equal-to 0.04. The Mossbauer spectra show that at concentrations where superconductivity disappears magnetic order, probably antiferromagnetism, is formed in the Cu(2) site. The phase diagram obtained is similar to those previously obtained for Y(1-x)Pr(x)Ba2(Cu(1-y)Fe(y))3O7+sigma [I. Felner et al., Phys. Rev. Lett. 65, 1945 (1990)]. In the superconducting region Fe atoms occupy only the Cu(1) sites and the Fe-57 Mossbauer spectrum contains only one doublet.