Intermolecular mechanism for multiple maxima in molecular dynamic susceptibility

TL;DR

This paper introduces a model explaining multiple maxima in molecular dynamic susceptibility at low temperatures, emphasizing the role of intermolecular interactions and relaxation processes, with good agreement to experimental data.

Contribution

It proposes a simple two-level system model that accounts for multiple maxima in susceptibility through intermolecular mechanisms and relaxation processes, extending understanding of low-temperature magnetic behavior.

Findings

Multiple maxima arise from intermolecular dipolar fields and relaxation processes.

The model aligns well with experimental observations across various systems.

Complex spectra and additional relaxation processes can lead to more maxima.

Abstract

A simple two-level system is introduced to demonstrate the existence of the intermolecular mechanism of the appearance/disappearance of multiple maxima in molecular dynamic susceptibility at low temperature. With minimum two relaxation processes, quantum tunneling induced by the nuclear spin bath and the direct process due to the spin-phonon interaction, we prove that the existence of a sufficiently wide dipolar field distribution in the experimental sample is the main cause of this phenomenon in zero or weak applied dc field. The correlations between the phenomenon and the applied dc field, temperature, or magnetic dilution of the sample are also investigated. Application to several experimental systems has shown a good agreement between the proposed theory and experiments. Cases with more complex multiplet spectrum, more relaxation processes,and possibility of more maxima in the molecular dynamic susceptibility are discussed.