Phase separation in Rb_xFe_2-ySe₂ probed by μSR

Authors have performed muon spin relaxation and rotation (μSR) measurements in single crystalline samples of superconducting (SC) R_xFe_2-ySe₂ (T_c = 29 K) and non-SC Rb_xFe_2-ySe₂ in order to elucidate whether there is difference of magnetic state between SC and non-SC systems and to clarify the relationship between superconductivity and antiferromagnetism. In the SC sample, they have found that SC volume fraction is less than about 10% and the rest is antiferromagnetic (AFM) phase, suggesting SC and AFM orderings are separated. They have also found that the magnetic state observed in the non-SC is different from that in the SC sample. It depends on temperature and seems to develop a new magnetic ordered state below 20 K, while no temperature dependence was observed in the SC sample. These results are consistent with results of Rb-NMR. (N.T.)