Origin of the unconventional magnetoresistance in Sr2FeMoO6

TL;DR

This study uncovers that a spin-glass surface layer around ferromagnetic grains and strong exchange coupling cause the unconventional magnetoresistance in Sr2FeMoO6, revealing the origin of the spin-valve type MR phenomenon.

Contribution

It introduces ac susceptibility measurements to probe the magnetic surface layer, revealing the spin-glass nature and exchange bias effects responsible for the anomalous MR.

Findings

Identification of a spin-glass like surface layer

Observation of strong exchange coupling and exchange bias

Explanation of the spin-valve type MR mechanism

Abstract

The unusual magnetoresistance (MR) behavior in Sr2FeMoO6, recently termed as spin-valve type MR (SVMR), presents several anomalies that are little understood so far. The difficulty in probing the origin of this phenomenon, arising from the magnetic property of only a small volume fraction of the ferromagnetic bulk, is circumvented in the present study by the use of ac susceptibility measurements that are sensitive to the slope rather than the magnitude of the magnetization. The present study unravels a spin-glass (SG) like surface layer around each soft ferromagnetic (FM) grain of Sr2FeMoO6. It is also observed that there is a very strong exchange coupling between the two, generating `exchange bias' effect, which consequently creates the `valve', responsible for the unusual MR effects.