Reversible Size Modification of Iron and Gallium Molecular Wheels: A Ga10 “Gallic Wheel” and Large Ga18 and Fe18 Wheels

King, Philippa; Stamatatos, Theocharis C.; Abboud, Khalil A.; Christou, George

doi:10.1002/anie.200602743

Cited by 127 publications

(90 citation statements)

References 66 publications

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“…21) (King et al, 2006). The system crystallizes in space group R3-and the molecule exhibits crystallographic S 6 symmetry.…”

Section: Antiferromagnetic Wheels With "Strong" Anisotropy and Quantumentioning

confidence: 99%

Magnetic Cluster Excitations

Fürrer

2010

Int. J. Mod. Phys. B

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Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the singlemolecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.

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“…21) (King et al, 2006). The system crystallizes in space group R3-and the molecule exhibits crystallographic S 6 symmetry.…”

Section: Antiferromagnetic Wheels With "Strong" Anisotropy and Quantumentioning

confidence: 99%

Magnetic Cluster Excitations

Fürrer

2010

Int. J. Mod. Phys. B

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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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confidence: 99%

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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“…In particular, molecular nanomagnets [4][5][6][7][8][9][10][11][12][13] have become prototype systems to probe the borders between quantum and classical physics, as well as to study decoherence in quantum systems [14,15].…”

Section: Introductionmentioning

confidence: 99%