Giant coercivity and high magnetic blocking temperatures for N23\u2212 radical-bridged dilanthanide complexes upon ligand dissociation

Selvan Demir,William J Evans,Jeffrey R Long,Lucy E Darago,Miguel I Gonzalez

doi:10.1038/s41467-017-01553-w

Abstract

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Herein, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (CpMe4H) capping ligands with strong magnetic exchange coupling provided by an N23− radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(CpMe4H2Tb)2(μ−{rm{N}}_2^ cdot)].

Highlights

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may inform the development of new bulk magnets
The potential application of such species in high-density information storage[1], as well as quantum computing[2] and spin-based electronics[3], hinges upon improving not just the defining thermal energy barrier to magnetization reversal, and the magnetic blocking temperature and coercive field—metrics that determine the ability of the molecules to retain information upon removal of an applied magnetic field 4
Progress in increasing blocking temperatures and coercive fields has been challenging mainly owing to the prevalence of through-barrier relaxation pathways, such as quantum tunneling of the magnetization, though recent reports on a molecule containing a single DyIII ion demonstrate Orbach relaxation proceeding through nearly the entire effective magnetization reversal barrier (Ueff) of greater than 1200 cm−1, with a correspondingly high 100-s blocking temperature[12, 13]

Summary

Introduction

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may inform the development of new bulk magnets. One strategy for suppressing quantum tunneling of the magnetization is to establish rigorously symmetry-protected pure MJ states[15], a condition asyet only experimentally achieved in adatom-surface experiments[16], though reports of the high-blocking temperature [Dy (Cpttt)2]+ (Cpttt = 1,2,4-tri(tert-butyl)cyclopentadienide) complex suggest that rigorous symmetry may not be crucial to achieve high performance in single-ion magnetic molecules[12, 13]. Another promising route is the design of systems with strong intramolecular magnetic coupling between two or more metal centers. 2-Tb exhibits the highest coercive field yet observed for any molecular magnet, substantially larger even than those of commercial permanent magnets, as well as the highest 100-s blocking temperature for a terbium single-molecule magnet

Methods

Results

Conclusion