Energy Level Lifetimes in the Single-Molecule Magnet Fe_8 : Experiments and Simulations

TL;DR

This study combines pump-probe experiments and theoretical modeling to measure and analyze the energy level lifetimes in the single-molecule magnet Fe_8, revealing the importance of multiple spin transition pathways and temperature effects.

Contribution

It provides the first experimental measurement of level lifetimes in Fe_8 and validates a spin-phonon coupling model including multiple transition types.

Findings

Level lifetimes agree with theoretical calculations

Both Δm_S = ±1 and ±2 transitions are necessary for accurate modeling

Temperature dependence helps determine spin-phonon coupling constants

Abstract

We present pump-probe measurements on the single-molecule magnet Fe_8 with microwave pulses having a length of several nanoseconds. The microwave radiation in the experiments is located in the frequency range between 104 GHz and 118 GHz. The dynamics of the magnetization of the single Fe_8 crystal is measured using micrometer-sized Hall sensors. This technique allows us to determine the level lifetimes of excited spin states, that are found to be in good agreement with theoretical calculations. The theory, to which we compare our experimental results, is based on a general spin-phonon coupling formalism, which involves spin transitions between nearest and next-nearest energy levels. We show that good agreement between theory and experiments is only obtained when using both the Delta m_S = +-1 transition as well as Delta m_S = +-2, where Delta m_S designates a change in the spin quantum number m_S. Temperature dependent studies of the level lifetimes of several spin states allow us finally to determine experimentally the spin-phonon coupling constants.