Non-adiabatic Landau-Zener transitions in low spin molecular magnet V15

TL;DR

This paper investigates the non-adiabatic Landau-Zener transitions in the low-spin molecular magnet V15, revealing a unique hysteresis phenomenon caused by environmental effects on quantum spin rotation.

Contribution

It demonstrates the occurrence of magnetic hysteresis in V15 despite lacking an energy barrier, highlighting environmental influence on quantum spin dynamics.

Findings

Observation of butterfly-shaped hysteresis loops

Hysteresis persists over several seconds

Environmental phonon effects influence spin transitions

Abstract

The V_{15} polyoxovanadate molecule is made of 15 spins 1/2 with antiferromagnetic couplings. It belongs to the class of molecules with very large Hilbert space dimension (2^{15} in V_{15}, 10^8 in Mn_{12}-ac). It is a low-spin/big-molecule with spin S=1/2. Contrary large-spins/big-molecules of the Mn_{12}-ac type, V_{15} has no energy barrier against spin rotation. Magnetization measurements have been performed and despite the absence of a barrier, magnetic hysteresis is observed over a timescale of several seconds. This new phenomenon characterized by a "butterfly" hysteresis loop is due to the effect of the environment on the quantum rotation of the entangled 15 spins of the molecule, in which the phonon density of states is not at its equilibrium (phonon bottleneck).