µ+SR Studies of Magnetic Properties of the YBa2Cu3OxSystem

Abstract
Samples of YBa 2 Cu 3 O x in four different phases have been probed by positive muon spin relaxation (µ + SR) method. Each phase was found to show different magnetic behavior. In the famous orthorhombic 90K superconductor ( x ∼6.9), neither magnetic ordering nor magnetic fluctuations were observed. However, in another orthorhombic superconducting phase ( x ∼6.4, T c ≈60 K) a magnetic fluctuation was observed below 7 K via muon spin-nuclear spin double relaxation. Its magnetic ordering temperature was expected to be below 2.4 K. Similar behavior was observed in an oxygen-rich ( x ∼6.5) tetragonal insulating phase, whereas the oxygen-deficient ( x ∼6.2) tetragonal insulating phase was found to be magnetically ordered, most likely antiferromagnetic, near room temperature. This is the first observation of a magnetically ordered state in the YBa 2 Cu 3 O x system.