Title: Oxygen Nuclear Magnetic Resonance Study of RuSr2EuCu2O8

Abstract: We report the results from a 17O Nuclear Magnetic Resonance (NMR) study of the high temperature superconducting cuprate (HTSC), RuSr2EuCu2O8. This compound has recently been found to exhibit the coexistence of magnetic order and superconductivity. At 9 T, the magnetic order in the RuO2 layers is predominately ferromagnetic. We measured the 17O NMR spectra from 10 K to 330 K and find the occurrence of an increasing 17O NMR shift with increasing temperature for temperatures above ~200 K, providing direct evidence that RuSr2RCu2O8 is similar to a very underdoped HTSC. The analysis of the NMR shift and spectral width of the 17O NMR line gives a small but measurable hyperfine field of ~9 mT from the Ru moment at the oxygen site in the copper oxygen planes. We show that the 17O NMR linewidth is governed by dipolar contributions from the Ru moment.