Pressure Dependence of the Magnetic Anisotropy in the "Single-Molecule Magnet" [Mn4O3Br(OAc)3(dbm)3]

TL;DR

This study investigates how hydrostatic pressure affects the magnetic anisotropy in a specific single-molecule magnet, revealing that increased pressure reduces the anisotropy and energy barrier, impacting its magnetic relaxation properties.

Contribution

It provides the first detailed analysis of pressure-induced changes in magnetic anisotropy in a Mn-based single-molecule magnet using inelastic neutron scattering.

Findings

Anisotropy parameter D decreases with pressure.

Energy barrier for magnetization relaxation is reduced under pressure.

Pressure causes tilting of Mn$^{3+}$ anisotropy axes, affecting magnetic properties.

Abstract

The anisotropy splitting in the ground state of the single-molecule magnet [Mn4O3Br(OAc)3(dbm)3] is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetisation relaxation at low temperatures. The value of the negative axial anisotropy parameter $D_{\rm cluster}$ changes from -0.0627(1) meV at ambient to -0.0603(3) meV at 12 kbar pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from 1.260(5) meV to 1.213(9) meV. Since the $\rm Mn-Br$ bond is significantly softer and thus more compressible than the $\rm Mn-O$ bonds, pressure induces a tilt of the single ion Mn$^{3+}$ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy.