Oxygen Anneal Effect on Single Crystalline Sr$_2$RhO$4-x$

Two dimensional perovskite-type transition metal oxides provide rich issues which originate from strong electron-electron correlation such as a spin triplet superconductivity in Sr2RuO4, quantum criticality at around the metamagnetic transition in Sr3Ru2O7 and antiferromagnetic metal phase in Ca3Ru2O7. We regard Rh oxides as another intriguing materials because of the similarity. Especially, Sr2RhO4 has been studied using single crystals grown by a floating-zone method. The importance of the oxygen content in Sr2RhO4 will be discussed based upon the results of electrical resistivity, magnetic susceptibility and specific heat.