Layered Antiferromagnetic State in (Nd_1-zLa_z)Sr₂Mn₂O₇

Abstract

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.