Magnetic-field-induced spin-crossover transition in [Mn$^{\textrm{III}}$(taa)] studied by X-ray absorption spectroscopy

TL;DR

This study investigates how high magnetic fields induce a spin-state change in a manganese complex using X-ray absorption spectroscopy, revealing a localized transition with hysteresis and remanence at low temperatures.

Contribution

It provides the first detailed analysis of magnetic-field-induced spin crossover in [Mn(taa)] using pulsed high magnetic fields and XANES, highlighting a microscopic transition mechanism.

Findings

Magnetic fields cause a spin crossover from low-spin to high-spin states.

Hysteresis and remanent magnetization observed at low temperatures.

Energy barrier for transition is 134K, lower than in similar compounds.

Abstract

The X-ray absorption near-edge structure (XANES) of Mn in a spin-crossover compound, [Mn$^{\textrm{III}}$(taa)], was studied in pulsed high magnetic fields up to 37T. By applying magnetic fields to the low-temperature low-spin (LS) state, significant changes in the spectra were observed, suggesting a magnetic-field-induced spin-crossover to the high-spin (HS) state. At low temperatures, the magnetic field dependence of the changes in the spectra exhibited hysteresis. Furthermore, when the magnetic field was set to zero, a considerable remanent component was observed. The energy barrier of the HS $\to$ LS transition was evaluated from the temperature dependence of the decay time of the remanent signal. The energy barrier of the transition was found to be 134K, which is notably lower than that for other spin-crossover compounds reported previously. Since the fraction of the field-induced HS state was at most 30% and the thermodynamic macroscopic field-induced phase transition was expected to occur in fields higher than 55T, the observed field-induced transition at low temperatures down to 17K could be understood as a localized microscopic transition at the single-molecular level.