Large magnetoresistance of the polycrystalline metamagnetic layered manganite La1.2Nd0.2Sr1.6Mn2O7

Magnetization and magnetotransport have been investigated for polycrystalline samples of the bilayer Ruddlesden-Popper compound La1.2Nd0.2Sr1.6Mn2O7 that shows the colossal magnetoresistance effect connected with ferromagnetic ordering at T-C=74 K. At T-2=38 K the compound reveals a transition from the ferromagnetic to an antiferromagnetic spin arrangement of alternating ferromagnetic bilayers, which undergoes a first order metamagnetic transition towards ferromagnetism in a magnetic field of similar to 3.5 kOe at 20 K. In measurements of resistance vs magnetic field, this transition is accompanied by a large resistance drop of [R(5 kOe)-R(0)]/R(0)=-60% at 5 K. The tunneling-like magnetoresistance (MR) known for current transport perpendicular to the layers in (La, Nd)(1.4)Sr1.6Mn2O7 single crystals contributes to this large MR observed in a polycrystalline sample. While current is expected to mainly follow the bilayers within the grains due to the anisotropy of conductivity, the high value of resistivity of our sample (similar to 8 Omega cm at 5 K) suggests that current paths are partially directed perpendicular to the layers. (C) 2000 American Institute of Physics. [S0021-8979(00)03102-9].