Cotunneling and non-equilibrium magnetization in magnetic molecular monolayers

TL;DR

This paper investigates how cotunneling processes influence transport and non-equilibrium magnetization in magnetic molecular monolayers, revealing significant magnetization changes and signatures of tunneling processes in the Coulomb-blockade regime.

Contribution

It introduces a master-equation approach beyond sequential tunneling to analyze magnetization and transport in magnetic molecular monolayers, highlighting cotunneling effects.

Findings

Magnetization changes significantly with small bias variations.

Inelastic cotunneling causes differential conductance steps and large magnetization shifts.

Magnetization exhibits signatures of sequential tunneling de-exciting molecular states.

Abstract

Transport and non-equilibrium magnetization in monolayers of magnetic molecules subject to a bias voltage are considered. We apply a master-equation approach going beyond the sequential-tunneling approximation to study the Coulomb-blockade regime. While the current is very small in this case, the magnetization shows changes of the order of the saturation magnetization for small variations of the bias voltage. Inelastic cotunneling processes manifest themselves as differential-conductance steps, which are accompanied by much larger changes in the magnetization. In addition, the magnetization in the Coulomb-blockade regime exhibits strong signatures of sequential tunneling processes de-exciting molecular states populated by inelastic cotunneling. We also consider the case of a single molecule, finding that cotunneling processes lead to the occurrence of magnetic sidebands below the Coulomb-blockade threshold. In the context of molecular electronics, we study how additional spin relaxation suppresses the fine structure in transport and magnetization.