A four-coordinate cobalt(II) single-ion magnet with coercivity and a very high energy barrier.

Yvonne Rechkemmer,Frank Neese,Biprajit Sarkar,Margarethe Van Der Meer,Frauke D Breitgoff,Milan Orlita,Mihail Atanasov,Michael Hakl,Joris Van Slageren,Petr Neugebauer

doi:10.1038/ncomms10467

Abstract

Single-molecule magnets display magnetic bistability of molecular origin, which may one day be exploited in magnetic data storage devices. Recently it was realised that increasing the magnetic moment of polynuclear molecules does not automatically lead to a substantial increase in magnetic bistability. Attention has thus increasingly focussed on ions with large magnetic anisotropies, especially lanthanides. In spite of large effective energy barriers towards relaxation of the magnetic moment, this has so far not led to a big increase in magnetic bistability. Here we present a comprehensive study of a mononuclear, tetrahedrally coordinated cobalt(II) single-molecule magnet, which has a very high effective energy barrier and displays pronounced magnetic bistability. The combined experimental-theoretical approach enables an in-depth understanding of the origin of these favourable properties, which are shown to arise from a strong ligand field in combination with axial distortion. Our findings allow formulation of clear design principles for improved materials.

Highlights

Single-molecule magnets display magnetic bistability of molecular origin, which may one day be exploited in magnetic data storage devices
The effective energy barrier Ueff is given by Ueff 1⁄4 D S2 for molecules with integer spin ground states and Ueff 1⁄4 D (S2À14) in the half-integer case
S is the spin of the ground state of the molecule and D is the magnetic anisotropy constant, more precisely, the second rank axial zero-field splitting (ZFS)

Summary

Introduction

Single-molecule magnets display magnetic bistability of molecular origin, which may one day be exploited in magnetic data storage devices. Mostly polynuclear coordination complexes of first row transition metals have been investigated in this respect For such systems, the effective energy barrier Ueff is given by Ueff 1⁄4 D S2 for molecules with integer spin ground states and Ueff 1⁄4 D (S2À14) in the half-integer case. Magnetic couplings are much easier to achieve and these ions are enjoying renewed interest as a result In this context, attention focusses on highanisotropy transition metal ions and it has been discovered that in a number of cases slow relaxation of the magnetization can be observed for mononuclear complexes, called single-ion magnets[14,15,16,17]. We present results of our investigations of the mononuclear tetrahedral cobalt(II) complex (HNEt3)2[CoII(L2À)2] (1), where H2L 1⁄4 1,2-bis(methanesulfonamido)benzene We show that this synthetically flexible, fully air- and moisture-stable complex has both a ZFS and an energy barrier exceeding 200 cmÀ1. Our findings completely unravel the origin of the advantageous properties of complex 1, and allow for the derivation of guidelines for further improvement

Methods

Results

Conclusion