Single-Molecule Magnets DyM2 N@C80 and Dy2 MN@C80 (M=Sc, Lu): The Impact of Diamagnetic Metals on Dy3+ Magnetic Anisotropy, Dy⋅⋅⋅Dy Coupling, and Mixing of Molecular and Lattice Vibrations.

Lukas Spree,Alexey A Popov,Stanislav M Avdoshenko,Aram Kostanyan,Bernd Büchner,Christin Schlesier,Rasmus Westerström,Thomas Greber

doi:10.1002/chem.201904879

Abstract

The substitution of scandium in fullerene single‐molecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the SMM performance of dysprosium nitride clusterfullerenes. The use of lutetium led to an improved SMM performance of DyLu2N@C80, which shows a higher blocking temperature of magnetization (T B=9.5 K), longer relaxation times, and broader hysteresis than DySc2N@C80 (T B=6.9 K). At the same time, Dy2LuN@C80 was found to have a similar blocking temperature of magnetization to Dy2ScN@C80 (T B=8 K), but substantially different interactions between the magnetic moments of the dysprosium ions in the Dy2MN clusters. Surprisingly, although the intramolecular dipolar interactions in Dy2LuN@C80 and Dy2ScN@C80 are of similar strength, the exchange interactions in Dy2LuN@C80 are close to zero. Analysis of the low‐frequency molecular and lattice vibrations showed strong mixing of the lattice modes and endohedral cluster librations in k‐space. This mixing simplifies the spin–lattice relaxation by conserving the momentum during the spin flip and helping to distribute the moment and energy further into the lattice.

Highlights

Enclosing lanthanide ions within the fullerene cage is a versatile route to a variety of molecular magnets.[1]
The substitution of scandium in fullerene singlemolecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the single-molecule magnets (SMMs) performance of dysprosium nitride clusterfullerenes
Results and Discussion ditional barrier and preventing zero-field quantum tunneling of magnetization (QTM).[3a]. The temperature dependence of the magnetization relaxation times in Dy2ScN@C80-Ih revealed a high barrier of 1735 K, because of the Orbach relaxation via the fifth Kramers doublet, in good agreement with CASSCF calculations.[2d]. Similar ferromagnetic interactions between dysprosium ions are present in Dy3N@C80-Ih, but the triangular arrangement of the dysprosium ions forbids simultaneous realization of ferromagnetic coupling for all three Dy···Dy contacts resulting in a frustrated ground state (Figure 1) with faster relaxation of magnetization than in the mono- and dinuclear analogues.[2a,3a] due to different cluster compositions and intramolecular Dy···Dy interactions, DySc2N@C80-Ih, Dy2ScN@C80-Ih, and Dy3N@C80-Ih exhibit substantially different SMM behavior at low temperatures

Summary

Introduction

Enclosing lanthanide ions within the fullerene cage is a versatile route to a variety of molecular magnets.[1] In particular, when non-metal atoms (C, N, O, S) are captured by the carbon cage together with lanthanides, the strong ionic interactions emerging in such endohedral clusterfullerenes may lead to a large magnetic anisotropy.[2] In addition, different magnetic states can emerge from the intramolecular interactions of lanthanide ions in clusterfullerenes.[2a,e,3] This combination of properties made lanthanide-clusterfullerenes promising candidates for single-molecule magnets (SMMs). Greber Physik-Institut der Universität Zürich Winterthurerstr. 190, 8057 Zürich (Switzerland)

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