Layered Antiferromagnetic State in (Nd_1-zLa_z)Sr₂Mn₂O₇

Abstract

Anisotropic magnetic and transport properties have been investigated for single crystals of (Nd 1- z La z )Sr 2 Mn 2 O 7 . 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 MnO 2 -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 µ 0 H =1 T.