Artificial ferroelectricity due to anomalous Hall effect in magnetic tunnel junctions

TL;DR

This paper theoretically demonstrates that magnetic tunnel junctions with insulating spacers can exhibit artificial ferroelectricity due to anomalous Hall effects, with potential for large spontaneous voltages.

Contribution

It introduces a novel mechanism where anomalous Hall effects induce artificial ferroelectricity in magnetic tunnel junctions with insulating barriers.

Findings

AHE and SHE have surface nature due to proximity effect.

AHE voltage in insulators can surpass that in metals.

Spontaneous Hall voltage exists at zero applied voltage in antiparallel configurations.

Abstract

We theoretically investigated Anomalous Hall Effect (AHE) and Spin Hall Effect (SHE) transversally to the insulating spacer O, in magnetic tunnel junctions of the form F/O/F where F are ferromagnetic layers and O represents a tunnel barrier. We considered the case of purely ballistic (quantum mechanical) transport, taking into account the assymetric scattering due to spin-orbit interaction in the tunnel barrier. AHE and SHE in the considered case have a surface nature due to proximity effect. Their amplitude is in first order of the scattering potential. This contrasts with ferromagnetic metals wherein these effect are in second (side-jump scattering) and third (skew scattering) order on these potentials. The value of AHE voltage in insulating spacer may be much larger than in metallic ferromagnetic electrodes. For the antiparallel orientation of the magnetizations in the two F-electrodes, a spontaneous Hall voltage exists even at zero applied voltage. Therefore an insulating spacer sandwiched between two ferromagnetic layers can be considered as exhibiting a spontaneous ferroelectricity.