The Kondo effect in magnetic impurities and ferromagnetic contacts

TL;DR

This paper demonstrates the coexistence of the Kondo effect and ferromagnetism in magnetic tunnel junctions with CoFe(B) nanodots, revealing spin-split zero-bias anomalies and their impact on tunneling magnetoresistance.

Contribution

It introduces a model combining Kondo physics with ferromagnetic contacts to explain observed conductance features in magnetic tunnel junctions.

Findings

Double peak conductance indicates spin-split zero-bias anomaly.

Kondo effect coexists with ferromagnetism in the system.

Suppression of tunneling magnetoresistance near zero bias.

Abstract

Planar macroscopic magnetic tunnel junctions exhibit well defined zero bias anomalies when a thin layer of ferromagnetic CoFe(B) nanodots is inserted within a MgO based tunnel barrier. The conductance curves exhibit a single and a double peak, respectively, for anti-parallel and parallel alignment of the magnetizations of the electrodes which sandwich the tunnel barrier. This leads to a suppression of the tunneling magnetoresistance near zero bias. We show that the double peak structure indicates that the zero-bias anomaly is spin-split due to a magnetic exchange interaction between the magnetic nanodots and the ferromagnetic electrodes. Using a model based on an Anderson quantum dot coupled to ferromagnetic leads, we show that these results imply the coexistence of a Kondo effect and ferromagnetism.