Hysteresis loops and adiabatic Landau-Zener-St\"uckelberg transitions in the magnetic molecule V$_6$

TL;DR

This study investigates the magnetic behavior of the V6 molecule, revealing hysteresis and magnetization steps explained by a generalized Bloch equation and Landau-Zener-Stückelberg transitions, highlighting quantum effects in molecular magnets.

Contribution

It provides a detailed analysis of hysteresis and magnetization steps in V6 molecules, introducing a generalized Bloch equation and demonstrating adiabatic Landau-Zener-Stückelberg transitions as the underlying mechanism.

Findings

Hysteresis loops observed at 1-5 K in V6 molecules.

Magnetization steps near zero magnetic field explained by Landau-Zener-Stückelberg transitions.

Theoretical modeling accurately reproduces experimental hysteresis behavior.

Abstract

We have observed hysteresis loops and abrupt magnetization steps in the magnetic molecule V$_6$, where each molecule comprises a pair of identical spin triangles, in the temperature range 1-5 K for external magnetic fields $B$ with sweep rates of several Tesla/ms executing a variety of closed cycles. The hysteresis loops are accurately reproduced using a generalization of the Bloch equation based on direct one-phonon transitions between the instantaneous Zeeman-split levels of the ground state (an $S=1/2$ doublet) of each spin triangle. The magnetization steps occur for $B\approx 0$ and they are explained in terms of adiabatic Landau-Zener-St\"{u}ckelberg transitions between the lowest magnetic energy levels as modified by inter-triangle anisotropic exchange of order 0.4 K.