Influence of the Coulomb interaction on the exchange coupling in granular magnets

TL;DR

This paper develops a theory showing how Coulomb blockade effects influence exchange coupling in granular magnets, revealing dependence on dielectric properties and grain size, with potential changes of tens of percent.

Contribution

It introduces a novel theoretical framework accounting for Coulomb blockade effects on exchange interactions in granular magnets, considering dielectric properties of the embedding matrix.

Findings

Exchange coupling decreases with lower dielectric permittivity.

Coulomb blockade effects can alter exchange interaction by up to 30-40%.

Exchange interaction depends on grain size and system parameters.

Abstract

We develop a theory of the exchange interaction between ferromagnetic (FM) metallic grains embedded into insulating matrix by taking into account the Coulomb blockade effects. For bulk ferromagnets separated by the insulating layer the exchange interaction strongly depends on the height and thickness of the tunneling barrier created by the insulator. We show that for FM grains embedded into insulating matrix the exchange coupling additionally depends on the dielectric properties of this matrix due to the Coulomb blockade effects. In particular, the FM coupling decreases with decreasing the dielectric permittivity of insulating matrix. We find that the change in the exchange interaction due to the Coulomb blockade effects can be a few tens of percent. Also, we study dependence of the intergrain exchange interaction on the grain size and other parameters of the system.