Charge Mobility and Dynamics in Spin-crossover Nanoparticles studied by Time-Resolved Microwave Conductivity

TL;DR

This study employs time-resolved microwave conductivity to analyze charge mobility and magnetic states in spin-crossover nanoparticles, revealing temperature-dependent regimes and charge transport mechanisms.

Contribution

It demonstrates TRMC as an effective tool for simultaneously assessing magnetic states and charge transport in SCO nanoparticles, providing new insights into their temperature-dependent behavior.

Findings

Identified two regimes in charge mobility around 225 K.

Observed activation-less and thermally activated hopping regimes.

Linked charge transport behavior to structural and thermal effects.

Abstract

We use the electrode-less time-resolved microwave conductivity (TRMC) technique to characterize spin-crossover (SCO) nanoparticles. We show that TRMC is a simple and accurate mean for simultaneously as-sessing the magnetic state of SCO compounds and charge transport information on the nanometre length scale. In the low-spin state from liquid nitrogen temperature up to 360 K the TRMC measurements present two well-defined regimes in the mobility and in the half-life times, possessing similar transition tempera-tures TR near 225 K. Below TR, an activation-less regime associated with short lifetimes of the charge carri-ers points at the presence of shallow-trap states. Above TR, these states are thermally released yielding a thermally activated hopping regime where longer hops increases the mobility and, concomitantly, the barrier energy. The activation energy could originate from intricate contributions such as polaronic self-localizations, but also from dynamic disorder due to phonons and/or thermal fluctuations of SCO moieties.