Phonon bottleneck effect leads to observation of quantum tunneling of the magnetization and butterfly hysteresis loops in(Et4N)3Fe2

Ralph Schenker

¹

,

Michael N. Leuenberger

²

,

Grégory Chaboussant

³

et al.

Abstract

A detailed investigation of the unusual dynamics of the magnetization of (Et4N)3Fe2F9 (Fe2), containing isolated [Fe2F9] 3− dimers, is presented and discussed. Fe2 possesses an S = 5 ground state with an energy barrier of 2.40 K due to an axial anisotropy. Poor thermal contact between sample and bath leads to a phonon bottleneck situation, giving rise to butterfly-shaped hysteresis loops below 5 K concomitant with slow decay of the magnetization for magnetic fields Hz applied along the Fe-Fe axis. The butterfly curves are reproduced using a microscopic model based on the interaction of the spins with resonant phonons. The phonon bottleneck allows for the observation of resonant quantum tunneling of the magnetization at 1.8 K, far above the blocking temperature for spin-phonon relaxation. The latter relaxation is probed by AC magnetic susceptibility experiments at various temperatures and bias fields HDC. At HDC = 0, no out-of-phase signal is detected, indicating that at T ≥ 1.8 K Fe2 does not behave as a single-molecule magnet. At HDC = 1 kG, relaxation is observed, occurring over the barrier of the thermally accessible S = 4 first excited state that forms a combined system with the S = 5 state.

Spin dynamics in single-molecule magnets combining surface acoustic waves and high-frequency electron paramagnetic resonance

“…16 Data collected for transitions within the stable well support this assertion, and the associated times required to establish equilibrium ͑ 100 ms͒ agree well with other studies. 17 However, for transitions within the metastable well, we are able to observe faster dynamics which are not influenced by the bottleneck.…”

Variation of Heterometallic Structural Motifs Based on [W(CN)8]3− Anions and MnII Ions as a Function of Synthetic Conditions

“…[42] Application of the DC bias field leads to the suppression of resonant tunneling due to the mismatch of magnetic sublevels and increases the activation barrier U for the thermally activated relaxation. [43] These results hint at the potential of a molecule of this type to behave as an SMM. Our further efforts in this vein will be directed at modifying the blocking ligand in order to achieve better separation between the molecules thereby decreasing intermolecular interactions.…”

First principles approach to the electronic structure, magnetic anisotropy and spin relaxation in mononuclear 3d-transition metal single molecule magnets

“…Phenomena of the given kind (phonon bottleneck) has been demonstrated experimentally in the S=1/2 quantum spin ground state of a V 15 polyoxometalate single molecule magnet [84] and in Fe 2 F 9 3-dimers with ferromagnetic Fe III -Fe III S=5 ground state [82].…”