Observation of the distribution of molecular spin states by resonant quantum tunneling of the magnetization

TL;DR

This study observes the distribution of molecular spin states in Fe magnetic clusters at very low temperatures using resonant quantum tunneling, revealing how the energy bias distribution evolves and broadens due to tunneling and nuclear spins.

Contribution

It introduces a new method to monitor the evolution of spin state distributions in molecular magnets through quantum tunneling effects.

Findings

Square-root time relaxation observed below 360 mK.

Tunneling creates a hole in the energy bias distribution.

Intrinsic broadening of the hole possibly due to nuclear spins.

Abstract

Below 360 mK, Fe magnetic molecular clusters are in the pure quantum relaxation regime and we show that the predicted square-root time relaxation is obeyed, allowing us to develop a new method for watching the evolution of the distribution of molecular spin states in the sample. We measure as a function of applied field H the statistical distribution P(\xi_H) of magnetic energy bias \xi_H$ acting on the molecules. Tunneling initially causes rapid transitions of molecules, thereby digging a hole in P(\xi_H) (around the resonant condition \xi_H = 0). For small initial magnetization values, the hole width shows an intrinsic broadening which may be due to nuclear spins.