Analysis of exchange interactions in dimers of Mn3 single-molecule magnets, and their sensitivity to external pressure

TL;DR

This study uses first-principles calculations to analyze magnetic exchange interactions in Mn3 dimers, revealing how external pressure can switch the coupling from ferromagnetic to antiferromagnetic, with implications for quantum information applications.

Contribution

It provides a detailed first-principles analysis of exchange interactions in Mn3 SMM dimers and demonstrates their sensitivity to external pressure, including a magnetic coupling switch.

Findings

Exchange coupling constant matches experimental data

Ligand groups influence magnetic interactions

Pressure induces a switch from ferromagnetic to antiferromagnetic

Abstract

In light of the potential use of single-molecule magnets (SMMs) in emerging quantum information science initiatives, we report first-principles calculations of the magnetic exchange interactions in [$\mathrm{Mn}_{3}$]$_{2}$ dimers of $\mathrm{Mn}_3$ SMMs, connected by covalently-attached organic linkers, that have been synthesized and studied experimentally by magnetochemistry and EPR spectroscopy. Energy evaluations calibrated to experimental results give the sign and order of magnitude of the exchange coupling constant ($J_{12}$) between the two $\mathrm{Mn}_{3}$ units that match with fits of magnetic susceptibility data and EPR spectra. Downfolding into the $\mathrm{Mn}$ $d$-orbital basis, Wannier function analysis has shown that magnetic interactions can be channeled by ligand groups that are bonded by van der Waals interaction and/or by the linkers via covalent bonding of specific systems, and effective tight-binding Hamiltonians are obtained. We call this long-range coupling that involves a group of atoms a collective exchange. Orbital projected spin density of states and alternative Wannier transformations support this observation. To assess the sensitivity of $J_{12}$ to external pressure, stress-strain curves have been investigated for both hydrostatic and uniaxial pressure, which have revealed a switch of $J_{12}$ from ferromagnetic to antiferromagnetic with increasing pressure.