Bias controlled Interlayer Exchange Coupling

TL;DR

This paper uses simulations and Green's functions to show that electrical bias can switch the sign of interlayer exchange coupling in ferromagnetic trilayers, depending on quantum states and conductance.

Contribution

It introduces a method to control interlayer exchange coupling sign via electrical bias in systems with quantum well states.

Findings

Bias can switch the coupling between parallel and anti-parallel states.

Quantum well states enable low switching current densities.

System conductance influences bias dependence of coupling.

Abstract

We demonstrate, using computer simulations and a non-equilibrium Greens function approach, that the sign of the out-of-equilibrium interlayer exchange coupling (ooeIEC) can change in the presence of an externally applied electrical bias. Our system consists of an insulating section connected to an exchange coupled ferromagnetic (FM) tri-layer, sandwiched between semi-infinite leads. When the exchange coupled trilayer contains a quantum-well state confined in the hybridisation gap (HG) of the FM, we find that a relatively small applied electrical bias can switch the lowest energy state of the tri-layer between parallel (P) and anti-parallel (AP) configurations. We consider three cases for the insulating section; a single tunnelling barrier, a resonant tunnelling barrier and an amorphous insulating barrier and, in each case, show that the bias dependence of the ooeIEC is strongly dependent on the system conductance. We find that the lowest switching current densities are achieved with strongly confined quantum well states.