An ordered stack of spin valves in a layered magnetoresistive perovskite

TL;DR

This paper investigates the magnetic structure of a layered manganite compound, revealing a field-induced transition from antiferromagnetic to ferromagnetic stacking, which explains its anisotropic magnetoresistance behavior.

Contribution

It provides the first neutron diffraction data on a manganite as a function of applied magnetic field, linking magnetic stacking changes to magnetoresistance.

Findings

Magnetic structure switches from antiferromagnetic to ferromagnetic stacking under applied field.

The material acts as a bulk stack of spin-valve devices.

Low-field magnetoresistance explained by spin-polarised tunnelling.

Abstract

The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of metallic MnO2 sheets separated by insulating material. The compound exhibits markedly anisotropic magnetoresistance at temperatures well below the three-dimensional magnetic ordering temperature TC=90 K in addition to colossal magnetoresistance around TC. We present neutron diffraction data which show that the magnetic structure of this material switches from antiferromagnetic stacking of the (ferromagnetically ordered) sheets in zero field to ferromagnetic stacking in a field of 1.5 Tesla. The data are the first to be collected on any manganite as a function of applied field, exactly as the magnetoresistance data themselves are collected. They provide a natural explanation of the low-field magnetoresistance in the ordered phase in terms of spin-polarised tunnelling between the magnetic layers and suggest that the material is a bulk stack of spin-valve devices.