Ordered Stack of Spin Valves in a Layered Magnetoresistive Perovskite

摘要

The layered compound consists of bilayers of metallic MnO2 sheets separated by211u001einsulating material. The compound exhibits markedly anisotropic magnetoresistance 211u001eat temperatures well below the three-dimensional magnetic ordering temperature 211u001eTc=90 K in addition to colossal magnetoresistance around Tc. The authors present 211u001eneutron diffraction data which show that the magnetic structure of this material 211u001eswitches from antiferromagnetic stacking of the (ferromagnetically ordered) 211u001esheets in zero field to ferromagnetics stacking in a field of 1.5 Telsa. The data 211u001eare the first to be collected on any manganite as a function of applied field, 211u001eexactly as the magnetoresistance data themselves are collected. They provide a 211u001enatural explanation of the low-field magnetoresistance in the ordered phase in 211u001eterms of spin-polarized tunneling between the magnetic layers and suggest that 211u001ethe material is a bulk stack of spin-valve devices.