Fe-substitution Effects on the Cu-spin Correlation in La_2-xSr_xCu_1-yFe_yO₄ Studied by Muon Spin Relaxation

We have investigated the low-frequency Cu-spin dynamics of partially Fe-substituted La_2-xSrxCu_1-yFeyO4 with x = 0.06-0.235 and y = 0.01 from zero-field muon-spin-relaxation measurements. We find that the magnetic transition temperature, T^mid_N, is enhanced through the 1% Fe substitution in a wide range of hole concentration per Cu, N p, where superconductivity appears in La_2-xSr_xCuO₄. The T^mid_N exhibits a local maximum at p ∼ 0.115 and exists even in the overdoped regime of p > 0.15. To the surprise, T^mid_N in the overdoped regime of 0.15 < p ≤ 0.225 is larger than in the underdoped regime of 0.05 ≤ p ≤ 0.09. These results suggest that the substitution of Fe as a magnetic impurity is effective for the stabilization of the so-called stripe order in high-T_c cuprates in the underdoped regime and that the nature of the magnetic order induced through the Fe substitution in the overdoped regime might be different from that in the underdoped regime.