Layered antiferromagnetic state in (Nd_1-zLa_z)Sr₂Mn₂O₇

Anisotropic magnetic and transport properties have been investigated for single crystals of (Nd_1-zLa_z)Sr₂Mn₂O₇. We have derived the magnetic phase diagram against the La concentration z and have found that the low-temperature state is of layered antiferromagnetic with alternating MnO₂-sheets. The reentrant-type charge-ordered state is observed in the limited z-region around z = 1.0 due to the released Jahn-Teller distortion. We further investigated magnetotransport properties for these antiferromagnetic manganites, and have found a large negative magnetoresistance, e.g., ρ_c(H)/ρ_c(0) ∼ 0.86 and ρ_ab(H)/ρ_ab(0) ∼ 0.88 at μ₀H = 1 T.