Gadolinium as an accelerator for reaching thermal equilibrium and its influence on the ground state of Dy2GdN@C80 single-molecule magnets

Aram Kostanyan,Bernd Büchner,Rasmus Westerström,Thomas Greber,Jan Dreiser,Christin Schlesier,Alexey A Popov,Fabian Fritz,Cinthia Piamonteze

doi:10.1103/physrevb.103.014404

Abstract

Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that the Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes faster equilibration in Dy2GdN@C80. This sheds light on the importance of the angular momentum balance in magnetic relaxation.

Highlights

A catalyst accelerates the approach of thermal equilibrium
The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium
The concept of a catalyst can as well be applied for the case of single molecule magnets (SMMs) that were prepared in a state outside thermal equilibrium towards which they decay with certain rates

Summary

Introduction

A catalyst accelerates the approach of thermal equilibrium. In the classical picture it lowers the kinetic barrier between two states A and B where the transition rates are described by Boltzmann factors comprising the barrier, the energy difference between A and B and by a prefactor reminiscent to an attempt frequency. The concept of a catalyst can as well be applied for the case of single molecule magnets (SMMs) that were prepared in a state outside thermal equilibrium towards which they decay with certain rates. In the present case the 4 f electron spins of a single gadolinium atom are shown to catalyze magnetic transition rates of the Dy2 dimer in Dy2GdN@C80 dramatically, which is due to the fact that Gd affects the ground state energies of the molecule

Methods

Results

Conclusion