Thermal spin-crossover and temperature-dependent zero-field splitting in magnetic nanographene chains

TL;DR

This study demonstrates thermal spin-crossover and temperature-dependent zero-field splitting in nanographene chains, revealing potential for quantum information and spintronics applications at the atomic scale.

Contribution

It introduces nanographene derivatives as models for thermal spin-crossover, showing experimental and theoretical evidence of spin state transitions and zero-field splitting.

Findings

Observation of spin-crossover at Tc in nanographene derivatives

Detection of zero-energy peak indicating spin transition

Temperature-dependent zero-field splitting in high-spin states

Abstract

Nanographene-based magnetism at interfaces offers an avenue to designer quantum materials towards novel phases of matter and atomic-scale applications. Key to spintronics applications at the nanoscale is bistable spin-crossover which however remains to be demonstrated in nanographenes. Here we show that antiaromatic 1,4-disubstituted pyrazine-embedded nanographene derivatives, which promote magnetism through oxidation to a non-aromatic radical are prototypical models for the study of carbon-based thermal spin-crossover. Scanning tunneling spectroscopy studies reveal symmetric spin excitation signals which evolve at Tc to a zero-energy peak, and are assigned to the transition of a S = 3/2 high-spin to a S = 1/2 low-spin state by density functional theory. At temperatures below and close to the spin-crossover Tc, the high-spin S= 3/2 excitations evidence pronouncedly different temperature-dependent excitation energies corresponding to a zero-field splitting in the Hubbard-Kanamori Hamiltonian. The discovery of thermal spin crossover and temperature-dependent zero-field splitting in carbon nanomaterials promises to accelerate quantum information, spintronics and thermometry at the atomic scale.