LOCAL MAGNETIC ORDER IN SUPERCONDUCTING YBA2(CU1-XMX)(3)O-7 (M = CO, FE)

We have examined the local magnetic order which is introduced into YBa 2CU3O7 by substituting low levels (1-4%) of Co or Fe. The order is evi denced through the appearance of an internal field on the spin of Yb-1 70(3+) Mossbauer probes diluted at the Y3+ sites. Low substitution lev els only marginally influence the superconducting properties, yet intr oduce local magnetic order over the whole sample volume. The local ord er concerns the Cu sublattices and fluctuates with rates that depend o n the substituted ion, its concentration, and the temperature.