Mononuclear Lanthanide Single-Molecule Magnets Based on Polyoxometalates

AlDamen, Murad A.; Clemente‐Juan, Juan M.; Coronado, Eugenio; Martí‐Gastaldo, Carlos; Gaita‐Ariño, Alejandro

doi:10.1021/ja801659m

Cited by 849 publications

(461 citation statements)

References 24 publications

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“…With this in mind, future efforts should be directed towards the implementation of magnetic ions possessing stronger spin-orbit anisotropy. Indeed, early studies of rare-earth-based mononuclear species are very promising [76]. III 3 Mn and (b) III 6 Mn : Mn -purple; O -brown; N -blue.…”

Section: Discussionmentioning

confidence: 99%

Magnetic quantum tunneling: insights from simple molecule-based magnets

et al. 2010

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This perspectives article takes a broad view of the current understanding of magnetic bistability and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on three families of relatively simple, low-nuclearity transition metal clusters: spin S = 4 II 4 Ni , III 3 Mn (S = 2 and 6) and III 6 Mn (S = 4 and 12). The Mn III complexes are related by the fact that they contain triangular III 3 Mn units in which the exchange may be switched from antiferromagnetic to ferromagnetic without significantly altering the coordination around the Mn III centers, thereby leaving the single-ion physics more-or-less unaltered. This allows for a detailed and systematic study of the way in which the individual-ion anisotropies project onto the molecular spin ground state in otherwise identical low-and high-spin molecules, thus providing unique insights into the key factors that control the quantum dynamics of SMMs, namely: (i) the height of the kinetic barrier to magnetization relaxation; and (ii) the transverse interactions that cause tunneling through this barrier. Numerical calculations are supported by an unprecedented experimental data set (17 different compounds), including very detailed spectroscopic information obtained from high-frequency electron paramagnetic resonance and low-temperature hysteresis measurements. Comparisons are made between the giant spin and multi-spin phenomenologies. The giant spin approach assumes the ground state spin, S, to be exact, enabling implementation of simple anisotropy projection techniques. This methodology provides a basic understanding of the concept of anisotropy dilution whereby the cluster anisotropy decreases as the total spin increases, resulting in a barrier that depends weakly on S. This partly explains why the record barrier for a SMM (86 K for Mn 6 ) has barely increased in the 15 years since the first studies of Mn 12 -acetate, and why the tiny Mn 3 molecule can have a barrier approaching 60% of this record. Ultimately, the giant spin approach fails to capture all of the key physics, although it works remarkably well for the purely ferromagnetic cases. Nevertheless, diagonalization of the multi-spin Hamiltonian matrix is necessary in order to fully capture the interplay between exchange and local anisotropy, and the resultant spin-state mixing which ultimately gives rise to the tunneling matrix elements in the high symmetry SMMs (ferromagnetic Mn 3 and Ni 4 ). The simplicity (low-nuclearity, high-symmetry, weak disorder, etc..) of the molecules highlighted in this study proves to be of crucial importance. Not only that, these simple molecules may be considered among the best SMMs: Mn 6 possesses the record anisotropy barrier, and Mn 3 is the first SMM to exhibit quantum tunneling selection rules that reflect the intrinsic symmetry of the molecule.

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Section: Discussionmentioning

confidence: 99%

Magnetic quantum tunneling: insights from simple molecule-based magnets

et al. 2010

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“…The major approach for the construction of such systems is to choose a ligand field (LF) which could offer an axial crystal field acting on the Ln III ion and stabilize the M J states with a large absolute value of the total angular momentum projection |M J |, therefore realizing a magnetization easy axis. Outstanding Ln based SMMs include Tb III /Dy III -phthalocyanin (Pc) double-decker complexes [13] and sandwiched Er III complexes with polyoxometallate based ligands [14]. Dinuclear Ln SMMs represent the simplest molecular units which permit the study of magnetic interactions between two spin carriers.…”

Section: Introductionmentioning

confidence: 99%

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

2016

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A class of two dinuclear dysprosium based complexes 1 and 2 were synthesized by employing salicyloylhydrazone derived pentadentate ligand (L). Structural analysis reveals that in complex 1, two Dy III centers are in muffin (C s ) coordination geometry while in 2, one Dy III center is in bicapped square antiprism (D 4d ) and other one is in triangular dodecahedron (D 2d ) coordination geometry. AC magnetic susceptibility measurements disclose that complexes 1 and 2 exhibit single-molecule magnet (SMM) behavior, with effective energy barrier of 36.4 and 9.7 K, respectively. The overall studies reveal that small differences in the coordination environment around the Dy III centers played a significant role in the difference in relaxation dynamics of the complexes. In order to elucidate the role of intermolecular interactions between nearby Dy III centers in the magnetic relaxation behavior, a diamagnetic isostructural Y III analog (3) was synthesized and magnetic behavior was examined.

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“…A further consequence of the large SOC is that the energy splitting of the quantum levels can be even larger than in TM. Single ion RE molecular magnets show ZFSs up to 54 meV [8][9][10][11][12], together with open hysteresis loops and magnetic lifetimes up to seconds at 3 K in the absence of an external field [13]. In addition, the strong localization of the 4f states leads to less hybridization with the surface, which could increase the lifetimes of the spin states.…”

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confidence: 99%

Magnetism of Ho and Er Atoms on Close-Packed Metal Surfaces

et al. 2014

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We investigated the magnetic properties of individual Ho atoms adsorbed on the (111) surface of Pt, which have been recently claimed to display single ion magnetic behavior. By combining x-ray absorption spectroscopy and magnetic dichroism measurements with ligand field multiplet calculations, we reveal a ground state which is incompatible with long spin relaxation times, in disagreement with former findings. A comparative study of the ground state and magnetic anisotropy of Ho and Er on Pt(111) and Cu(111) emphasizes the different interaction of the 4f orbitals with localized and delocalized substrate states. In particular, we find a striking rotation of the magnetization easy axis for Er, which changes from out of plane on Pt(111) to in plane on Cu(111). DOI: 10.1103/PhysRevLett.113.237201 PACS numbers: 75.30.Gw, 32.10.Dk, 75.10.Dg, 78.70.Dm Single atoms adsorbed on a solid surface represent a paradigm for investigating the ultimate size limit of a magnet [1][2][3][4][5][6]. For transition-metal (TM) atoms, the reduced coordination on surface sites results in the survival of a large orbital moment, for which the spin-orbit coupling (SOC) may create magnetic anisotropies of the order of ten [1,7] or several tens of meV [6]. In such quantum systems, the magnetic anisotropy is conveniently defined as the zerofield splitting (ZFS), the energy difference between the magnetic ground and first excited state. However, a large ZFS is only a necessary but not a sufficient condition for magnetic bistability. The angular symmetry of the magnetic anisotropy created by the crystal field (CF) of the surface determines the symmetry of the quantum states and thereby their coupling by tunnel matrix elements. This enables or disables magnetization reversal by tunneling. Additional mechanisms limiting the spin relaxation times are the scattering with substrate electrons and the interaction between the electron and nuclear spin of the magnetic atom. A close to ideal cylindrical CF environment and a ZFS of 58 meV have been reported for Co atoms on MgO/Ag(100); however, the spin-relaxation times, albeit reaching a record for TM atoms, remained relatively short with a lower bound of 230 μs [6].A promising alternative to 3d elements are the 4f rareearth (RE) elements. Their SOC is generally larger than the CF and therefore the magnetic states are eigenstates of the total angular momentum J and its z component J z . A further consequence of the large SOC is that the energy splitting of the quantum levels can be even larger than in TM. Single ion RE molecular magnets show ZFSs up to 54 meV [8][9][10][11][12], together with open hysteresis loops and magnetic lifetimes up to seconds at 3 K in the absence of an external field [13]. In addition, the strong localization of the 4f states leads to less hybridization with the surface, which could increase the lifetimes of the spin states. Rare earth atoms on a surface are of interest as model single ion magnets since the CF in the hollow adsorption sites has a dominant axial component, akin...

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Mononuclear Lanthanide Single-Molecule Magnets Based on Polyoxometalates

Cited by 849 publications

References 24 publications

Magnetic quantum tunneling: insights from simple molecule-based magnets

Magnetic quantum tunneling: insights from simple molecule-based magnets

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

Magnetism of Ho and Er Atoms on Close-Packed Metal Surfaces

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