Multiple nearest-neighbor exchange model for the frustrated magnetic molecules Mo72Fe30 and Mo72Cr30

TL;DR

This study introduces a probabilistic nearest-neighbor exchange model to accurately describe the magnetic behavior of frustrated molecules Mo72Fe30 and Mo72Cr30, accounting for variations in exchange interactions.

Contribution

It proposes a two-parameter distribution of exchange constants in a classical Heisenberg model, improving agreement with experimental susceptibility data.

Findings

Excellent match with experimental dM/dH measurements achieved

Distribution of exchange interactions captures microscopic disorder effects

Model explains field and temperature dependence of magnetic response

Abstract

Our measurements of the differential susceptibility dM/dH of the frustrated magnetic molecules Mo72Fe30 and Mo72Cr30 reveal a pronounced dependence on magnetic field (H) and temperature (T) in the low H - low T regime, contrary to the predictions of existing models. Excellent agreement with experiment is achieved upon formulating a nearest-neighbor classical Heisenberg model where the 60 nearest-neighbor exchange interactions in each molecule, rather than being identical as has been assumed heretofore, are described by a two-parameter probability distribution of values of the exchange constant. We suggest that the probability distribution provides a convenient phenomenological platform for summarizing the combined effects of multiple microscopic mechanisms that disrupt the idealized picture of a Heisenberg model based on a single value of the nearest-neighbor exchange constant.