Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study

TL;DR

This study uses ^{139}La NMR to show that magnetic fields induce ferromagnetic order above the Curie temperature in La_{1.2}Sr_{1.8}Mn_2O_7, linking this to the colossal magnetoresistance effect.

Contribution

It reveals that field-induced ferromagnetism above T_C causes the CMR effect in a double-layered manganite, providing new insights into its origin.

Findings

Field-induced ferromagnetism persists up to 330 K.

Maximum CMR coincides with saturation of magnetic moments.

Indicates double exchange interaction drives metallic state.

Abstract

In order to gain insights into the origin of colossal magneto-resistance (CMR) in manganese oxides, we performed a ^{139}La NMR study in the double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie temperature T_C=126 K, applying a magnetic field induces a long-range ferromagnetic order that persists up to T=330 K. The critical field at which the induced magnetic moment is saturated coincides with the field at which the CMR effect reaches to a maximum. Our results therefore indicate that the CMR observed above T_C in this compound is due to the field-induced ferromagnetism that produces a metallic state via the double exchange interaction.