Field Of Single-molecule Magnets Research Articles

Slow magnetic relaxation and photoluminescence behaviors of dilanthanide complexes bearing N8O2 donor macrocyclic ligand

On account of the complicated magnetic exchange interactions between lanthanide ions, binuclear lanthanide complexes have broad application prospect in the field of single-molecule magnets. Therefore, it is necessary to develop reasonable bridging ligands to manipulate the directional assembly of binuclear lanthanide complexes. Herein, we selected the macrocyclic ligand LN8O2 to build up two new dilanthanide complexes [Ln2(LN8O2) (OpyO)2(H2O)2](NO3)2 (1-Ln, Ln = Dy, Tb; LN8O2 = hexamethyl-tetraaza-dioxe-dipyrazolacycloicosaphane-2,9,12,19-tetraene; OpyOH = 2-pyridinol-1-oxide). Dynamic magnetic studies show that 1-Dy exhibits slow relaxation behavior under a 1 kOe applied field. Further fitting analysis of relaxation times gives the effective energy barrier of 38.2 cm−1, and reveals that the slow magnetic relaxation behavior is dominated by the Orbach and Raman processes. High-resolution luminescence emission spectrum indicates the energy gap of 36.8 cm−1 between the ground state and the first excited state, consistent with the magnetic measurement results. 1-Tb exhibits brilliant characteristic green light emission under UV light excitation. The absolute quantum yield of 1-Tb is 44.8%, and its first-order fitted decay lifetime is 779.21 μs at room temperature. This study provides the way for directional construction of high-performance molecular materials with magnetic and optical dual-function.

Heterometallic 3d/4f-Metal Complexes: Structure and Magnetism

In the past two decades, tremendous progress has been made in the field of single-molecule magnets (SMMs), which not only achieves breakthroughs in various key indicators (flipping energy barrier and hysteresis temperature), but also expands SMMs of various types (3d, 4f, 3d–4f and 5f) and different connection methods. Among the many different types of SMM mentioned above, the SMM based on the 4f metal center has made the biggest breakthrough. Introducing 3d metal ions into lanthanide complexes to form 3d–4f heterometallic complexes can promote strong magnetic exchange between multiple metal centers, resulting in magnetic properties different from 3d and 4f complexes. Therefore, the expansion of the structure and magnetic properties of 3d–4f heterometallic complexes can promote the progress in the field of SMM. In this review, we summarize the structure and magnetic properties of 3d–4f heterometallic complexes formed by different types of organic ligands.

Single-Molecule Magnets: From Mn12-ac to dysprosium metallocenes, a travel in time

• A brief introduction concerning origin and detection of Single-Molecule Magnets. • A time travel in single-molecule magnetism. • Highly anisotropic systems are prevailing over high nuclearity metal clusters. • Synergistic multifunctionality, a key feature in molecular magnetism. • Hybrid materials based on Single-Molecule Magnets, towards future devices. The discovery of the first Single-Molecule Magnet, Mn12-ac, in 1993 changed the perspective of how information can be stored. The current bit, occupying few hundreds of nanometers in present devices, would be minimized to tens of angstroms at molecular level. However, until a couple of years these materials could only operate at temperatures near to the absolute zero. From 1993 to date, the field of Single-Molecule Magnets (SMMs) has continuously evolved thanks to the close collaboration of chemists and physicists obtaining materials already operating above the liquid nitrogen temperature. This long journey, however, has involved the study of many different routes towards high performance SMMs, being each of them essential in order to deeply understand the quantum dynamics behind these molecules. An era of high spin 3d metal clusters was the beginning of everything, but it went through highly anisotropic low coordinate 3d compounds, lanthanide based magnets, radical bridged compounds and 3d-4f mixed systems, among others, to end up in the current state of the art dysprosium metallocenes. Furthermore, after the magnetic studies in bulk, SMM based hybrid systems are emerging for future application devices, which also involve very interesting multifunctionalities. All in all, this work aims to explain how these materials work and show the trajectory and some of the major advances that have been made during recent years in this field.

Endohedral metallofullerene single molecule magnets

Nanoscale magnetic materials have been attracting enormous interests during the past few decades due to the rapid development of high-density magnetic storage devices. A breakthrough in nanomagnetism is the discovery of single molecule magnets (SMMs), which exhibit slow relaxation and quantum tunneling of the magnetization resulted from a molecular-based blocking anisotropy, and thus have potential applications in high-density data storage, molecular spintronics and quantum computing. Since the report of Mn12-complex as the first SMM by Sessoli et al. in 1993, a large number of SMMs based on organometallic coordination compounds have been synthesized. Compared to the traditional bulk magnets, the magnetic properties of SMMs are determined by their instrinsic spin structures resulting in slow magnetic relaxation. SMM is characterized by a bi-stable magnetic ground state and a certain spin-reversal barrier ( U eff). Additionally, hysteresis loops can be observed below the blocking temperature ( T B). Therefore, SMMs with excellent magnetic properties always have high T B and U eff. U eff depends strongly on spin ground state ( S ) and magneto-crystalline anisotropy ( D ), and can be expressed with the formula U eff =| D|S 2. For transition metal-based SMMs, their low magneto-crystalline anisotropies ( D ) result in relative low U eff. In recent years, lanthanide based SMMs have been studied intensively and become the most promising high-performance SMMs, owning to their strong single ion anisotropy. Encapsulating metal atoms or metallic clusters into fullerene cages generate a special class of fullerenes, the so-called endohedral metallofullerenes (EMFs), for which the encapsulation of metal atoms endow EMFs more fascinating properties compared to empty fullerenes. For instance, EMFs are paramagnetic when the entrapped metal ions have unpaired electrons. Furthermore, EMFs were able to show excellent SMM properties when the encapsulated clusters induce appropriate ligand-fields. EMFs with lanthanide open up a new avenue in the field of SMMs in 2012 when single molecule magnetism was proved for the metal nitride clusterfullerene (NCF) DySc2N@ I h-C80. Fullerene cages are stable in air and thus they can protect the magnetic ions from ambient conditions, and the negatively charged nonmetallic atom(s) within the cluster and the negatively charged carbon atoms of fullerene cages provide magnetic anisotropy which is necessary for single molecule magnetism. Moreover, the molecular structures of EMFs can be modulated by varying the encapsulated metal ions, metal cluster and cage isomer; hence the research on EMF-SMMs has been developed rapidly since 2012. Up to now, metal nitride clusterfullerenes (NCFs), metal carbide clusterfullerenes (CCFs), metal oxide clusterfullerenes (OCFs), metal sulfide clusterfullerenes (SCFs), metal cyanide clusterfullerenes (CYCFs) and dimetallofullerenes (di-EMFs) have been confirmed as SMMs. In this paper, we present an exhaustive review on all kinds of EMF-SMMs reported to date including their 1D, 2D and 3D assemblies. We mainly discuss the influences of the types and the numbers of the encapsulated metal ions and non-metal atoms on the magnetic properties of EMF-SMMs. Finally, the prospects and challenges of EMF-SMMs are also discussed.

Recent advance on single molecule magnets

Molecules which exhibit a macroscopically measurable slow relaxation of their magnetization are named single molecule magnets (SMMs). SMMs mainly including transition meatal SMMs (TM-SMMs) and lanthanide SMMs (Ln-SMMs) have received much attention in recent years as they can behave as quantum objects showing potential applications covering quantum computing, high-density data storage devices and spintronics. This review highlights the recent breakthroughs in the field of SMMs with special focus on synthetic strategies towards high-performance SMMs.

Coupling Influences SMM Properties for Pure 4 f Systems.

Increasing both the energy barrier for magnetization reversal and the coercive field of the hysteresis loop are significant challenges in the field of single-molecule magnets (SMMs). Coordination geometries of lanthanide ions and magnetic interactions between lanthanide ions are both important for guiding the magnetic behavior of SMMs. We report a high energy barrier of 657 K (457 cm-1 ) in a diamagnetic-ion-diluted lanthanide chain compound with a constrained bisphenoid symmetry (D2d ); this energy barrier is substantially higher than the barrier of 567 K (394 cm-1 ) of the non-diluted chain compound with intrachain ferromagnetic interactions. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops, which is crucial for the rational design of high-performance SMMs. Factors related to the coordination sphere of the lanthanide center, which govern the high magnetic relaxation barriers through the second excited Kramer's doublets and the magnetic interactions that affect the hysteresis loops, were revealed through ab initio calculations.

Supramolecular architectures for controlling slow magnetic relaxation in field-induced single-molecule magnets

In order for molecular magnetic materials to become functional, they must retain their magnetization at reasonable temperatures implying high energy barriers for spin reversal. The field of single-molecule magnets (SMMs) has recently experienced an explosion of research targeting these high anisotropic barriers. Achieving such feats has involved increasing the spin of a complex and/or increasing the inherent magnetic anisotropy. Exerting control over the total spin of a complex has been possible contrary to controlling the global anisotropy. Herein, we report the experimental and theoretical study of local anisotropy alignment on DyIII metal centers and their orientation relative to other centers in rare, dinuclear quadruply-stranded helicate/mesocate complexes. A detailed study of these supramolecular architectures has advanced our knowledge of the origins of magnetic relaxation in SMMs which was shown to arise from minute changes in bond distances around the metal centers leading to changes in the local anisotropy and, in turn, the effective energy barriers.

ChemInform Abstract: Relaxation Dynamics of Dysprosium(III) Single Molecule Magnets

AbstractReview: 106 refs.

Relaxation dynamics of dysprosium(iii) single molecule magnets

Over the past decade, lanthanide compounds have become of increasing interest in the field of Single Molecule Magnets (SMMs) due to the large inherent anisotropy of the metal ions. Heavy lanthanide metal systems, in particular those containing the dysprosium(III) ion, have been extensively employed to direct the formation of a series of SMMs. Although remarkable progress is being made regarding the synthesis and characterization of lanthanide-based SMMs, the understanding and control of the relaxation dynamics of strongly anisotropic systems represents a formidable challenge, since the dynamic behaviour of lanthanide-based SMMs is significantly more complex than that of transition metal systems. This perspective paper describes illustrative examples of pure dysprosium(III)-based SMMs, published during the past three years, showing new and fascinating phenomena in terms of magnetic relaxation, aiming at shedding light on the features relevant to modulating relaxation dynamics of polynuclear lanthanide SMMs.

Single Molecule Magnets under Pressure

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