  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.
