Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field

TL;DR

This study investigates how transverse magnetic fields influence the quantum tunneling and ferromagnetic ordering in Mn12 single-molecule magnets, revealing a potential quantum critical point at high fields.

Contribution

It demonstrates the field-dependent transition from ferromagnetic order to a disordered state in Mn12 magnets using neutron diffraction.

Findings

Quantum tunneling is induced by transverse magnetic fields.

Ferromagnetic order appears below 0.9 K at low fields.

Long-range ferromagnetic correlations diminish above 5.5 T.

Abstract

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. Application of a magnetic field perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular interactions turn this equilibrium state into a ferromagnetically ordered phase. However, long range ferromagnetic correlations nearly disappear for fields larger 5.5 T, possibly suggesting the existence of a quantum critical point.