  In order to investigate the electronic state of Ce-free and Ce-underdoped
high-Tc cuprates with the so-called T' structure, we have performed
muon-spin-relaxation (muSR) and specific-heat measurements of Ce-free
T'-La_1.8_Eu_0.2_CuO_4+d_ (T'-LECO) polycrystals and Ce-underdoped
T'-Pr_1.3-x_La_0.7_Ce_x_CuO_4+d_ (T'-PLCCO) single crystals with x=0.10. The
muSR spectra of the reduced superconducting samples of both T'-LECO with Tc=15K
and T'-PLCCO with x=0.10 and Tc=27K have revealed that a short-range magnetic
order coexists with the superconductivity in the ground state. The formation of
a short-range magnetic order due to a tiny amount of excess oxygen in the
reduced superconducting samples strongly suggest that the Ce-free and
Ce-underdoped T'-cuprates are regarded as strongly correlated electron systems.
