A search for magnetic resonance of ruthenium in octahedral coordination with oxygen

We have searched, without success, for microwave-frequency magnetic resonance of Ru4+ and Ru5+ ions in a number of materials for which the Ru are in octahedral coordination with six oxygen. A number of ruthenates including RuO2, SrRuO3, Sr3Ru2O7, Ba3Ru2NiO9, Ba2GdRuO6, Sr2YRuO6, and Ba2YRuO6, which include paramagnetic, antiferromagnetic, and ferromagnetic spin configurations, have been examined. We present analysis which shows that the last material provides an optimized opportunity to detect antiferromagnetic Ru resonance for temperatures less than TN=39 K; none is detected for frequencies as high as 35 GHz in magnetic fields up to μoH=2 T. This result indicates that the antiferromagnetic magnon energy gap exceeds the energy associated with the signal frequency. SrRuO3 is a known ferromagnetic contaminant phase in the rutheno-cuprates. We report neutron diffraction measurements on SrRuO3, finding it to have an appreciable local moment at low temperatures, 1.25(0.1)μB; this moment vanishes near 165 K. We show that it also fails to exhibit ferromagnetic resonance, at least in the range 10-35 GHz. As a result of the diffraction and resonance studies, it is concluded that the reports of ferromagnetic resonance in superconducting rutheno-cuprates are actually due to antiferromagnetically ordered Cu in these materials, and the presence of even a few percent of SrRuO3 as a potential contaminant is of little importance.