Butterfly Hysteresis and Slow Relaxation of the Magnetization in (Et4N)3Fe2F9: Manifestations of a Single-Molecule Magnet

TL;DR

This study reports on the magnetic hysteresis and slow relaxation phenomena in a specific iron fluoride complex, demonstrating single-molecule magnet behavior at very low temperatures due to quantum tunneling and phonon interactions.

Contribution

It provides the first detailed analysis of butterfly hysteresis and slow relaxation in (Et4N)3Fe2F9, linking these effects to quantum tunneling and phonon dynamics in a single-molecule magnet.

Findings

Hysteresis observed below 5 K with a butterfly shape.

Relaxation timescale of minutes indicating slow magnetization relaxation.

Energy barrier of 2.40 K due to the S=5 dimer ground state.

Abstract

(Et4N)3Fe2F9 exhibits a butterfly--shaped hysteresis below 5 K when the magnetic field is parallel to the threefold axis, in accordance with a very slow magnetization relaxation in the timescale of minutes. This is attributed to an energy barrier Delta=2.40 K resulting from the S=5 dimer ground state of [Fe2F9]^{3-} and a negative axial anisotropy. The relaxation partly occurs via thermally assisted quantum tunneling. These features of a single-molecule magnet are observable at temperatures comparable to the barrier height, due to an extremely inefficient energy exchange between the spin system and the phonons. The butterfly shape of the hysteresis arises from a phonon avalanche effect.