Successive magnetic ordering sequence observed from muon spin rotation in T'-structured R2CuO4 (R = Eu, Nd)

The magnetic behavior and effects of oxygen-reduction annealing on the magnetism of T'-structured R2CuO4 (R = Eu and Nd), which is the parent compound of electron-doped cuprate superconductors, have been investigated from muon spin rotation (muSR) measurements. In the muon time spectra of as-sintered R2CuO4, an oscillation component with a small amplitude and a dominant exponential-type decay component were observed for the temperature range between 150 K and TN1 (=250-270 K). This observation suggests an inhomogeneous magnetic phase of a fluctuating spin state and a locally ordered spin state at these temperatures. With decreasing temperature,the small oscillation component disappears, and the exponential one develops below 150 K. Upon further cooling, well-defined oscillation spectra corresponding to uniform long-ranged magnetic order emerge below TN2 = 110 K. Except for the absence of the small oscillation component, similar magnetic behavior is confirmed for the annealed compounds. Therefore, the successive development of magnetism characterized by the fluctuating spin state over a wide temperature range is a common feature for T'-R2CuO4. We discuss a possible picture for the ordering sequence in T'-R2CuO4 and the origin of the small oscillation component in the as-sintered compounds from the viewpoint of local defects.