Butterfly hysteresis curve is a signature of adiabatic Landau-Zener transition

TL;DR

This paper demonstrates that butterfly hysteresis curves in low-spin magnetic molecules are signatures of adiabatic Landau-Zener transitions, not phonon bottlenecks, supported by analytical magnetization dynamics modeling.

Contribution

It provides a new interpretation of butterfly hysteresis curves as adiabatic Landau-Zener transitions, challenging previous phonon bottleneck explanations.

Findings

Butterfly hysteresis curves are signatures of adiabatic Landau-Zener transitions.

Reversible behavior occurs near zero magnetic field with bounded susceptibility.

Analytical model qualitatively matches experimental observations.

Abstract

We stress that the so-called butterfly hysteresis curves observed in dynamical magnetization measurements on systems of low-spin magnetic molecules such as V-15 and V-6 are a signature of adiabatic Landau-Zener transitions rather than that of a phonon bottleneck. We investigate the magnetization dynamics analytically with the help of a simple relaxation theory in the basis of the adabatic energy levels of the spin 1/2, to a qualitative accordance with experimental observations. In particular, reversible behavior is found near zero field, the corresponding susceptibility being bounded by the equilibrium and adiabatic susceptibilities from below and above, respectively.