Engineering atomic-scale magnetic fields by dysprosium single atom magnets.
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ABSTRACT:
SUBMITTER: Singha A
PROVIDER: S-EPMC8263604 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Geometry and magnetic relaxation modulations in a series of mononuclear dysprosium complexes, [DyLz2(o-vanilin)2]·X·solvent (Lz = 6-pyridin-2-yl-[1,3,5]triazine-2,4-diamine; X = Br- (1), NO3- (2), CF3SO3- (3)), were realized by changing the nature of the counter-anion. The DyIII ions in all complexes are eight-coordinate and in approximate D4d symmetry environments. The magnetic relaxation and anisotropy of these complexes were systematically investigated, both experimentally and from ab initio calculations. All complexes exhibit excellent single-molecule magnetic behavior. Remarkably, magneto-structural studies show that the rotation of the coordinating plane of the square-antiprismatic environment in complex 2 induces a magnetic relaxation path through higher excited states, yielding a high anisotropy barrier of 615 K (696 K for a diluted sample). Additionally, obvious opening of the hysteresis loop is observed up to 7 K, which is the highest blocking temperature ever reported for dysprosium single-molecule magnets.
| S-EPMC6008742 | biostudies-literature
Project description:A series of dysprosium(iii) metallocenium salts, [Dy(CpiPr4R)2][B(C6F5)4] (R = H (1), Me (2), Et (3), iPr (4)), was synthesized by reaction of DyI3 with the corresponding known NaCpiPr4R (R = H, iPr) and novel NaCpiPr4R (R = Me, Et) salts at high temperature, followed by iodide abstraction with [H(SiEt3)2][B(C6F5)4]. Variation of the substituents in this series results in substantial changes in molecular structure, with more sterically-encumbering cyclopentadienyl ligands promoting longer Dy-C distances and larger Cp-Dy-Cp angles. Dc and ac magnetic susceptibility data reveal that these structural changes have a considerable impact on the magnetic relaxation behavior and operating temperature of each compound. In particular, the magnetic relaxation barrier increases as the Dy-C distance decreases and the Cp-Dy-Cp angle increases. An overall 45 K increase in the magnetic blocking temperature is observed across the series, with compounds 2-4 exhibiting the highest 100 s blocking temperatures yet reported for a single-molecule magnet. Compound 2 possesses the highest operating temperature of the series with a 100 s blocking temperature of 62 K. Concomitant increases in the effective relaxation barrier and the maximum magnetic hysteresis temperature are observed, with 2 displaying a barrier of 1468 cm-1 and open magnetic hysteresis as high as 72 K at a sweep rate of 3.1 mT s-1. Magneto-structural correlations are discussed with the goal of guiding the synthesis of future high operating temperature DyIII metallocenium single-molecule magnets.
| S-EPMC6256727 | biostudies-literature
Project description:Single-molecule magnets (SMMs) are coordination compounds that exhibit magnetic bistability below a characteristic blocking temperature. Research in this field continues to evolve from its fundamental foundations towards applications of SMMs in information storage and spintronic devices. Synthetic chemistry plays a crucial role in targeting the properties that could ultimately produce SMMs with technological potential. The ligands in SMMs are invariably based on non-metals; we now report a series of dysprosium SMMs (in addition to their magnetically dilute analogues embedded in yttrium matrices) that contain ligands with the metalloid element antimony as the donor atom, i.e. [(η5-Cp'2Dy){μ-Sb(H)Mes}]3 (1-Dy) and [(η5-Cp'2Dy)3{μ-(SbMes)3Sb}] (2-Dy), which contain the stibinide ligand [Mes(H)Sb]- and the unusual Zintl-like ligand [Sb4Mes3]3-, respectively (Cp' = methylcyclopentadienyl; Mes = mesityl). The zero-field anisotropy barriers in 1-Dy and 2-Dy are Ueff = 345 cm-1 and 270 cm-1, respectively. Stabilization of the antimony-ligated SMMs is contingent upon careful control of reaction time and temperature. With longer reaction times and higher temperatures, the stibine pro-ligands are catalytically dehydrocoupled by the rare-earth precursor complexes. NMR spectroscopic studies of the yttrium-catalysed dehydrocoupling reactions reveal that 1-Y and 2-Y are formed during the catalytic cycle. By implication, 1-Dy and 2-Dy should also be catalytic intermediates, hence the nature of these complexes as SMMs in the solid-state and as catalysts in solution introduces a strategy whereby new molecular magnets can be identified by intercepting species formed during catalytic reactions.
| S-EPMC5399632 | biostudies-literature
Project description:Single-molecule magnets are a type of coordination compound that can retain magnetic information at low temperatures. Single-molecule magnets based on lanthanides have accounted for many important advances, including systems with very large energy barriers to reversal of the magnetization, and a di-terbium complex that displays magnetic hysteresis up to 14?K and shows strong coercivity. Ligand design is crucial for the development of new single-molecule magnets: organometallic chemistry presents possibilities for using unconventional ligands, particularly those with soft donor groups. Here we report dysprosium single-molecule magnets with neutral and anionic phosphorus donor ligands, and show that their properties change dramatically when varying the ligand from phosphine to phosphide to phosphinidene. A phosphide-ligated, trimetallic dysprosium single-molecule magnet relaxes via the second-excited Kramers' doublet, and, when doped into a diamagnetic matrix at the single-ion level, produces a large energy barrier of 256?cm(-1) and magnetic hysteresis up to 4.4?K.
| S-EPMC4507012 | biostudies-literature
Project description:The interest for chiral tris(β-diketonato)lanthanide complexes in coordination chemistry is huge due to its Lewis acid character, optical activity, and the control of the final compound architecture. The reaction of equimolar quantities of [Dy((-)/(+)hfc)3 (H2 O)] (hfc- = 3-(heptafluoropropylhydroxymethylene)-(+/-)-camphorate) and L led to the formation of a pair of enantiomers for dinuclear complexes [Dy((-)/(+)hfc)3 (L)]2 ⋅C7 H16 ([(-)/(+)1]⋅C7 H16 ) (L = 4'-(4'''-pyridyl-N-oxide)-1,2':6'1''-bis-(pyrazolyl)pyridine]). Starting from the previous experimental protocol with the addition of bulky BArF anions, a partial dissociation of the chiral [Dy((-)/(+)hfc)3 (H2 O)] was observed leading to the isolation of a mono-dimensional cationic chiral polymer {[Dy((-)/(+)hfc)2 (L)][BarF]}n ⋅nCH3 NO2 ([(-)/(+)2]n ⋅nCH3 NO2 ). Natural circular dichroism (NCD) highlighted an exciton CD couplet for [(-)/(+)2]n but not for (-)/(+)1. The latter behaves as a single-molecule magnet (SMM) with a blocking temperature up to 4 K, whereas [(-)/(+)2]n is a 1D assembly of field-induced SMMs with a magnetic relaxation occurring through a Raman process only.
| S-EPMC10107933 | biostudies-literature
Project description:The structures and magnetic properties of the arsenic- and selenium-ligated dysprosium single-molecule magnets (SMMs) [Cp'3Dy(AsH2Mes)] (3-Dy), [(η5-Cp'2Dy){μ-As(H)Mes}]3 (4-Dy), [Li(thf)4]2[(η5-Cp'2Dy)3(μ3-AsMes)3Li] ([Li(thf)4]2[5-Dy]), and [(η5-Cp'2Dy){μ-SeMes}]3 (6-Dy) are described. The arsenic-ligated complexes 4-Dy and 5-Dy are the first SMMs to feature ligands with metalloid elements as the donor atoms. The arsenide-ligated complex 4-Dy and the selenolate-ligated complex 6-Dy show large anisotropy barriers in the region of 250 cm-1 in zero d.c. field, increasing to 300 cm-1 upon 5% magnetic dilution. Theoretical studies reveal that thermal relaxation in these SMMs occurs via the second-excited Kramers' doublet. In contrast, the arsinidene-ligated SMM 5-Dy gives a much smaller barrier of 23 cm-1, increasing to 35 cm-1 upon dilution. The field-dependence of the magnetization for 4-Dy and 5-Dy at 1.8 K show unusual plateaus around 10 kOe, which is due to the dominance of arsenic-mediated exchange over the dipolar exchange. The effects of the exchange interactions are more pronounced in 5-Dy, which is a consequence of a small but significant increase in the covalent contribution to the predominantly ionic dysprosium-arsenic bonds. Whereas the magnetically non-dilute dysprosium SMMs show only very narrow magnetization versus field hysteresis loops at 1.8 K, the impact of magnetic dilution is dramatic, with butterfly-shaped loops being observed up to 5.4 K in the case of 4-Dy. Our findings suggest that ligands with heavier p-block element donor atoms have considerable potential to be developed more widely for applications in molecular magnetism.
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Project description:The central goals of nanoscale magnetic materials science are the self-assembly of the smallest structure exhibiting ferromagnetic hysteresis at room temperature, and the assembly of these structures into the highest density patterns. The focus has been on chemically ordered alloys combining magnetic 3d elements with polarizable 5d elements having high spin-orbit coupling and thus yielding the desired large magneto-crystalline anisotropy. The chemical synthesis of nanoparticles of these alloys yields disordered phases requiring annealing to transform them to the high-anisotropy L1(0) structure. Despite considerable efforts, so far only part of the nanoparticles can be transformed without coalescence. Here we present an alternative approach to homogeneous alloys, namely the creation of nanostructures with atomically sharp bimetallic interfaces and interlines. They exhibit unexpectedly high magnetization reversal energy with values and directions of the easy magnetization axes strongly depending on chemistry and texture. We find significant deviations from the expected behaviour for commonly used element combinations. Ab-initio calculations reproduce these results and unravel their origin.
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Project description:Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon(ii), halide-capped complexes [Fe4(tpda)3Cl2] (1Cl) and [Fe4(tpda)3Br2] (1Br), obtained by reacting iron(ii) dihalides with [Fe2(Mes)4] and N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine (H2tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mössbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with χMT at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron(ii) ions in each derivative was explored by ab initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy (D = -11 to -19 cm-1, |E/D| = 0.05-0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy (D = 8-10 cm-1, |E/D| = 0.06-0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1-Fe2 and Fe3-Fe4 interactions and antiferromagnetic Fe2-Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field.
| S-EPMC8214398 | biostudies-literature
Project description:Atomic engineering is envisioned to involve selectively inducing the desired dynamics of single atoms and combining these steps for larger-scale assemblies. Here, we focus on the first part by surveying the single-step dynamics of graphene dopants, primarily phosphorus, caused by electron irradiation both in experiment and simulation, and develop a theory for describing the probabilities of competing configurational outcomes depending on the postcollision momentum vector of the primary knock-on atom. The predicted branching ratio of configurational transformations agrees well with our atomically resolved experiments. This suggests a way for biasing the dynamics toward desired outcomes, paving the road for designing and further upscaling atomic engineering using electron irradiation.
| S-EPMC6524980 | biostudies-literature
Project description:Electron-phonon coupling is important in many physical phenomena, e.g. photosynthesis, catalysis and quantum information processing, but its impacts are difficult to grasp on the microscopic level. One area attracting wide interest is that of single-molecule magnets, which is motivated by searching for the ultimate limit in the miniaturisation of binary data storage media. The utility of a molecule to store magnetic information is quantified by the timescale of its magnetic reversal processes, also known as magnetic relaxation, which is limited by spin-phonon coupling. Several recent accomplishments of synthetic organometallic chemistry have led to the observation of molecular magnetic memory effects at temperatures above that of liquid nitrogen. These discoveries have highlighted how far chemical design strategies for maximising magnetic anisotropy have come, but have also highlighted the need to characterise the complex interplay between phonons and molecular spin states. The crucial step is to make a link between magnetic relaxation and chemical motifs, and so be able to produce design criteria to extend molecular magnetic memory. The basic physics associated with spin-phonon coupling and magnetic relaxation was outlined in the early 20th century using perturbation theory, and has more recently been recast in the form of a general open quantum systems formalism and tackled with different levels of approximations. It is the purpose of this Tutorial Review to introduce the topics of phonons, molecular spin-phonon coupling, and magnetic relaxation, and to outline the relevant theories in connection with both the traditional perturbative texts and the more modern open quantum systems methods.
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