[Fe(OMe)2(O2CCH2Cl)]10, a Molecular Ferric Wheel

Taft, Kingsley L.; Delfs, Christopher D.; Papaefthymiou, Georgia C.; Foner, S.; Gatteschi, Dante; Lippard, Stephen J.

doi:10.1021/ja00082a001

Cited by 459 publications

(379 citation statements)

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“…These magnetization and torque steps are frequently observed [24], e.g. in molecular ferric wheels [13,14,15,16]. However, as we will show now, the level mixing at the LCs lead also to peak-like contributions in the torque (but not the magnetization).…”

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confidence: 65%

Quantum Magneto-Oscillations in a Supramolecular Mn(II)-[3×3] Grid

et al. 2004

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The magnetic grid molecule Mn(II)- [3 × 3] has been studied by high-field torque magnetometry at 3 He temperatures. At fields above 5 T, the torque vs. field curves exhibit an unprecedented oscillatory behavior. A model is proposed which describes these magneto oscillations well.PACS numbers: 33.15. Kr, 75.10.Jm Among the known magneto-oscillatory effects, the de Haas-van Alphen (dHvA) effect in metals (and the group of effects related to it) is the most prominent example, having had a formative influence on our modern picture of solid state physics [1]. The dHvA effect originates from a quantization of closed electron orbits into Landau levels in a magnetic field, so that the density of states at the Fermi energy exhibits a markedly oscillatory evolution as a function of magnetic field. Currently, it finds application in a wide range of materials, e.g. heavy fermion compounds [2], low-dimensional organic metals [3], hightemperature superconductors [4], two-dimensional electron gases [5], or in the recently discovered superconductor MgB 2 [6].In this work, we report on a new magnetooscillatory effect, discovered in the molecular nanomagnet [Mn 9 (2POAP-2H) 6 ](ClO 4 ) 6 · 3.57 MeCN · H 2 O, the so called Mn-[3 × 3] grid. Molecular nanomagnets are compounds with many magnetic metal ions linked by organic ligands to form well defined magnetic nanoclusters. They have attracted much interest since they can exhibit fascinating quantum effects at the mesoscopic scale. For instance, quantum tunneling of the magnetization has been observed in the clusters Mn 12 or Fe 8 [7]. We have performed high-field torque magnetometry on the Mn-[3 × 3] grids at 3 He temperatures and observed striking magneto oscillations in the torque signal. We show that they arise from the interplay between antiferromagnetic interactions within a molecule and Zeeman splitting on the one hand and the magnetic anisotropy on the other hand.In the Mn-[3 × 3] grid molecules, nine spin-5/2 Mn(II) ions occupy the positions of a regular 3 × 3 matrix, held in place by a lattice of organic ligands [inset of Fig. 1]. These grids were characterized recently by magnetization and torque measurements and found to exhibit unusual magnetic properties [8]. The Mn ions within a molecule experience an antiferromagnetic interaction leading to a total spin S = 5/2 ground state at zero field. At a field of about 7 T, the ground state changes abruptly to a new state, a S = 7/2 level, accompanied by a change of the sign of the magnetic anisotropy. Notably, intermolecular magnetic interactions are at best on the order of few 10 mK. This is evident from the crystal structure (the smallest separation between two molecules in the crystal is > 8Å), but has been checked also experimentally [9]. Accordingly, even at 3 He temperatures the magnetism of a macroscopic crystal sample reflects that of a single molecule.Single crystals of Mn-[3 × 3] were prepared as reported [10]. They crystallize in the space group C 2 /c. The cation [Mn 9 (2POAP-2H) 6 ] 6+ exhibits a slightly dis...

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Quantum Magneto-Oscillations in a Supramolecular Mn(II)-[3×3] Grid

et al. 2004

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“…For certain systems this behaviour has been explained with the help of the underlying sublattice structure [2]. Experimentally this property has been described as "following the Landé interval rule" [3,4,5,6]. In the classical limit, where the single-spin quantum number s goes to infinity, the function E min (S) is even an exact parabola if the system possesses co-planar ground states [7].…”

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Independent magnon states on magnetic polytopes

et al. 2001

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For many spin systems with constant isotropic antiferromagnetic nextneighbour Heisenberg coupling the minimal energies E min (S) form a rotational band, i. e. depend approximately quadratically on the total spin quantum number S, a property which is also known as Landé interval rule. However, we find that for certain coupling topologies, including recently synthesised icosidodecahedral structures this rule is violated for high total spins. Instead the minimal energies are a linear function of total spin. This anomaly results in a corresponding jump of the magnetisation curve which otherwise would be a regular staircase.

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“…Recent attempts with the AFM molecular wheels CsFe 8 and Fe 10 were encouraging steps forward [10,11], but were criticized with arguments that the tunneling actions S 0 / are too small and the NVT picture only approximately valid [11]. The latter attempts were stimulated by the theoretical prediction of NVT in such wheels [7], and that its observation would be assisted by the monodispersity and crystallinity inherent in molecular compounds, and their resulting well defined structural and magnetic parameters [4,12,13,14].We here present measurements of the magnetic torque (τ = M × B), magnetization, and inelastic neutron scattering (INS) on the AFM molecular wheel [Fe 18 (pd) 12 -(pdH) 12 (O 2 CEt) 6 (NO 3 ) 6 ](NO 3 ) 6 , or Fe 18 (Fig. 1a).…”

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Quantum Phase Interference and Néel-Vector Tunneling in Antiferromagnetic Molecular Wheels

et al. 2009

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The antiferromagnetic molecular wheel Fe18 of eighteen exchange-coupled Fe III ions has been studied by measurements of the magnetic torque, the magnetization, and the inelastic neutron scattering spectra. The combined data show that the low-temperature magnetism of Fe18 is very accurately described by the Néel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory. In addition, the magnetic torque as a function of applied field exhibits oscillations that reflect the oscillations in the NVT tunnel splitting with field due to quantum phase interference.PACS numbers: 75.50. Xx, 33.15.Kr, 75.10.Jm Although magnetism is a priori quantum mechanical, observation of genuine quantum phenomena such as tunneling and phase interference in magnets is difficult. This is because in ferro-or ferrimagnets, the low-temperature magnetism and dynamics are by and large well described by the magnetization vector M obeying classical equations, although for magnetic molecules (e.g. Mn 12 , Fe 8 ), tunneling of the magnetization and phase interference have been observed [1]. Antiferromagnets, however, exhibit zero magnetization in the ground state, and observation of quantum behavior is even more challenging.Antiferromagnets can be described by the Néel vector n = (M A − M B )/(2M 0 ), with sublattice magnetizations M A , M B of length M 0 (Fig. 1b). In three dimensions, they exhibit long-range Néel order, but domains enable thermally activated or even quantum fluctuations of the Néel vector [2]. Nanosized, single-domain antiferromagnetic (AFM) clusters would provide clean systems to study Néel-vector dynamics, but mono-dispersity is then a key issue. In small particles with weak magnetic anisotropy, the Néel vector can rotate [3,4], while with strong anisotropy it is localized in distinguishable directions, but fluctuates by quantum tunneling, i.e., Néel-vector tunneling (NVT) [5,6,7]. Typically, there are two tunneling paths (Fig. 1c) and interference occurs due to the phase of the wave function. This gives rise to characteristic oscillations in the tunnel splitting as function of applied magnetic field, which would be observable in static measurements such as magnetization [7].Initial attempts to establish NVT with the ferritin protein [8] unfortunately proved controversial owing to polydisperse samples and the presence of uncompensated magnetization [9]. Recent attempts with the AFM molecular wheels CsFe 8 and Fe 10 were encouraging steps forward [10,11], but were criticized with arguments that the tunneling actions S 0 / are too small and the NVT picture only approximately valid [11]. The latter attempts were stimulated by the theoretical prediction of NVT in such wheels [7], and that its observation would be assisted by the monodispersity and crystallinity inherent in molecular compounds, and their resulting well defined structural and magnetic parameters [4,12,13,14].We here present measurements of the magnetic torque (τ = M × B), magnetization, and inelastic neutron scattering (INS) on the AFM molecular wheel [...

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[Fe(OMe)2(O2CCH2Cl)]10, a Molecular Ferric Wheel

Cited by 459 publications

References 3 publications

Quantum Magneto-Oscillations in a Supramolecular Mn(II)-[3×3] Grid

Quantum Magneto-Oscillations in a Supramolecular Mn(II)-[3×3] Grid

Independent magnon states on magnetic polytopes

Quantum Phase Interference and Néel-Vector Tunneling in Antiferromagnetic Molecular Wheels

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