Exploiting single-ion anisotropy in the design of f-element single-molecule magnets
TL;DR: In this paper, a qualitative method for predicting the ligand architectures that will generate magnetic anisotropy for a variety of f-element ions is presented to guide the design of stronger single-molecule magnets incorporating the f-elements.
Abstract: Scientists have long employed lanthanide elements in the design of materials with extraordinary magnetic properties, including the strongest magnets known, SmCo5 and Nd2Fe14B. The properties of these materials are largely a product of fine-tuning the interaction between the lanthanide ion and the crystal lattice. Recently, synthetic chemists have begun to utilize f-elements—both lanthanides and actinides—for the construction of single-molecule magnets, resulting in a rapid expansion of the field. The desirable magnetic characteristics of the f-elements are contingent upon the interaction between the single-ion electron density and the crystal field environment in which it is placed. This interaction leads to the single-ion anisotropies requisite for strong single-molecule magnets. Therefore, it is of vital importance to understand the particular crystal field environments that could lead to maximization of the anisotropy for individual f-elements. Here, we summarize a qualitative method for predicting the ligand architectures that will generate magnetic anisotropy for a variety of f-element ions. It is hoped that this simple model will serve to guide the design of stronger single-molecule magnets incorporating the f-elements.
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2,206 citations
TL;DR: Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations, indicating that magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
Abstract: Magnetic hysteresis is observed in a dysprosocenium complex at temperatures of up to 60 kelvin, the origin of which is the localized metal–ligand vibrational modes unique to dysprosocenium. The discovery of molecules that exhibit magnetic bistability raised hopes for the use of such molecular systems as tiny building blocks for magnetic data storage. Despite a quarter of a century of research, however, the temperatures at which these molecules display their desirable magnetic properties remain frustratingly low. Conrad Goodwin et al. report the synthesis and characterization of a molecular dysprosocenium complex that shows magnetic bistability up to 60 kelvin—tantalizingly close to liquid nitrogen temperatures, the point at which applications would start to become a realistic possibility. Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements include reading and manipulating single nuclear spins1,2, exploiting atomic clock transitions for robust qubits3 and, most recently, magnetic data storage in single atoms4,5. Single-molecule magnets exhibit magnetic hysteresis of molecular origin6—a magnetic memory effect and a prerequisite of data storage—and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets7, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin8,9,10 using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates11,12 (for example, 30 kelvin with 200 oersted per second)12. Here we report a hexa-tert-butyldysprosocenium complex—[Dy(Cpttt)2][B(C6F5)4], with Cpttt = {C5H2tBu3-1,2,4} and tBu = C(CH3)3—which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal–ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
1,328 citations
TL;DR: Two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior are reported.
Abstract: Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.
835 citations
TL;DR: In this paper, the authors demonstrate the research developed in the few years in the fascinating and challenging field of Dy-based SMMs with particular focus on how recent studies tend to address the issue of relaxation dynamics in these systems from synthetic point of view.
800 citations
TL;DR: A monometallic dysprosium complex is reported that shows the largest effective energy barrier to magnetic relaxation of Ueff =1815(1) K, approaching proposed schemes for high-temperature single-molecule magnets (SMMs).
Abstract: We report a monometallic dysprosium complex, [Dy(OtBu)2(py)5][BPh4] (5), that shows the largest effective energy barrier to magnetic relaxation of Ueff=1815(1) K. The massive magnetic anisotropy is due to bis-trans-disposed tert-butoxide ligands with weak equatorial pyridine donors, approaching proposed schemes for high-temperature single-molecule magnets (SMMs). The blocking temperature, TB , is 14 K, defined by zero-field-cooled magnetization experiments, and is the largest for any monometallic complex and equal with the current record for [Tb2N2{N(SiMe3)2}4(THF)2].
721 citations
References
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TL;DR: In this article, it was shown that the magnetization of the Mn12 cluster is highly anisotropic and the magnetisation relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis.
Abstract: MAGNETIC materials of mesoscopic dimensions (a few to many thousands of atoms) may exhibit novel and useful properties such as giant magnetostriction, magnetoresistivity and magnetocaloric effects1–4. Such materials also allow one to study the transition from molecular to bulk-like magnetic behaviour. One approach for preparing mesoscopic magnetic materials is to fragment bulk ferromagnets; a more controllable method is to take a 'bottom-up' approach, using chemistry to grow well defined clusters of metal ions5,6. Lis7 has described a twelve-ion manganese cluster in which eight of the Mn ions are in the +3 oxidation state (spin S=2) and four are in the +4 state (S=3/2). These ions are magnetically coupled to give an S=10 ground state8, giving rise to unusual magnetic relaxation properties8,9. Here we report that the magnetization of the Mn12 cluster is highly anisotropic and that the magnetization relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis. This behaviour is not, however, strictly analogous to that of a bulk ferromagnet, in which magnetization hysteresis results from the motion of domain walls. In principle, a bistable magnetic unit of this sort could act as a data storage device.
3,327 citations
TL;DR: This work reviews the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules, and discusses the advantages over more conventional materials, and the potential applications in information storage and processing.
Abstract: A revolution in electronics is in view, with the contemporary evolution of the two novel disciplines of spintronics and molecular electronics. A fundamental link between these two fields can be established using molecular magnetic materials and, in particular, single-molecule magnets. Here, we review the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules. We discuss the advantages over more conventional materials, and the potential applications in information storage and processing. We also outline current challenges in the field, and propose convenient schemes to overcome them.
2,694 citations
TL;DR: In this article, an implementation of Grover's algorithm that uses molecular magnets was proposed, which can be used to build dense and efficient memory devices based on the Grover algorithm, in which one single crystal can serve as a storage unit of a dynamic random access memory device.
Abstract: Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers1 and in searching a database2 by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system3, the superposition of single-particle quantum states is sufficient for Grover's algorithm4. Recently, the latter has been successfully implemented5 using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets6,7,8,9,10, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 105, with access times as short as 10-10 seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.
2,378 citations
TL;DR: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property and a significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs.
Abstract: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.
2,124 citations