The molecular approach to nanoscale magnetism

Caneschi, Andréa; Gatteschi, Dante; Sangregorio, Claudio; Sessoli, Roberta; Sorace, Lorenzo; Cornia, Andrea; Novak, M.A.; Paulsen, C.; Wernsdorfer, Wolfgang

doi:10.1016/s0304-8853(99)00408-4

Cited by 210 publications

(150 citation statements)

References 66 publications

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“…This result is in good agreement with the experimental value H 0 = 0.22 T [6,8]. It can be immediately seen that for this value of the external paralel magnetic field the original minimum at φ = π and the maxima at φ = π/2 and φ = 3π/2 have turned into a single maximum of the potential function, while the only surviving minimum is the one at φ = 0 (= 2π).…”

supporting

confidence: 80%

“…One of the interesting aspects that came out of these studies is the possibility of measuring spin tunneling in mesoscopic systems what corresponds, in a standard quantum description, to the tunneling of the collective degree of freedom corresponding to the magnetization direction through a potential barrier separating two minima of an effective potential associated with the spatial orientation [1,2,3,4,5,6,7,8].…”

mentioning

confidence: 99%

“…This spin system has a j = S = 10 ground state and a suggested pure quantum spin tunneling below 0. 6,8], and k B is Boltzmann's constant respectively. On the other hand, from a pure algebraic model point of view, it is interesting to see that the Lipkin quasi-spin model [16] of wide use in many-body physics is also obtained by just considering D = 0.…”

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confidence: 99%

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Quantum description of spin tunneling in magnetic molecules

Galetti

2007

Physica A: Statistical Mechanics and its Applications

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Abstract.A new approach is used that allows to describe the magnetic molecules main properties in a direct and simple way. Results obtained for the F e 8 cluster show good agreement with the experimental data.PACS numbers: 03.65. Ca, 75.45+j, 75.60Jp Submitted to: J. Phys. C: Solid State Phys.In recent years, with the experimental advances in the measurement of magnetic molecular clusters properties, it has emerged a new frontier in this area. One of the interesting aspects that came out of these studies is the possibility of measuring spin tunneling in mesoscopic systems what corresponds, in a standard quantum description, to the tunneling of the collective degree of freedom corresponding to the magnetization direction through a potential barrier separating two minima of an effective potential associated with the spatial orientation [1,2,3,4,5,6,7,8].From the theoretical point of view, spin tunneling has been treated mainly by the use of a WKB method adapted to spin systems [9,10], by using Feyman's path integral treatment of quantum mechanics [11,12], and also by using su(2) coherent states [13] in order to establish a correspondence between the spectrum of the spin system with the energy levels of a particle moving in an effective potential [14].In the present letter we intend to show that still another approach may be used for describing spin tunneling -in angle representation -in such a way that analytic expressions for the characteristic parameters of the magnetic molecular clusters can be obtained; in particular, the results for the spectrum and energy barrier heights are directly obtained and the spin tunneling process can be easily interpreted.The starting point of the present approach is the introduction of a quantum phenomenological Hamiltonian describing the spin system, written in terms of angular momentum operators obeying the standard commutation relations, and that reflects

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confidence: 80%

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confidence: 99%

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Quantum description of spin tunneling in magnetic molecules

Galetti

2007

Physica A: Statistical Mechanics and its Applications

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“…The molecule, Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ·2CH 3 COOH·4H 2 O, is one of the most thoroughly studied [5][6][7][8][9][10] …”

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confidence: 99%

Films of Mn12-acetate by pulsed laser evaporation

Meenakshi

Teizer

Naugle

et al. 2004

Solid State Communications

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Films of the molecular nanomagnet, Mn 12 -acetate, have been deposited using pulsed laser deposition and a novel variant, matrix assisted pulsed laser evaporation. The films have been characterized by X-ray photoelectron spectroscopy, mass spectrometry and magnetic hysteresis. The results indicate that an increase in laser energy and/or pulse frequency leads to fragmentation of Mn 12 , whereas its chemical and magnetic integrity is preserved at low laser energy (200 mJ). This technique allows the fabrication of patterned thin film systems of molecular nanomagnets for fundamental and applied experiments.

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“…Each molecule functions as a nanoscale, single-domain magnetic particle that, below its blocking temperature, exhibits the classical macroscale property of a magnet, namely magnetization hysteresis. Such a molecule straddles the classical/quantum interface in also displaying quantum tunneling of magnetization [4,5,6,7,8,9,10] and quantum phase interference [11,12,13]. A quantitative understanding of the mechanism of magnetization tunneling is being developed.…”

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Spin-Spin Cross Relaxation in Single-Molecule Magnets

et al. 2002

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It is shown that dipolar and weak superexchange interactions between the spin systems of singlemolecule magnets (SMM) play an important role in the relaxation of magnetization. These interactions can reduce or increase resonant tunneling. At certain external fields, the mechanism of spin-spin cross-relaxation (SSCR) can lead to quantum resonances which can show up in hysteresis loop measurements as well defined steps. A Mn4 SMM is used as a model system to study the SSCR which plays also an important role for other SMMs like Mn12 or Fe8.PACS numbers: PACS numbers: 75.45.+j, 75.60.Ej Single-molecule magnets (SMMs) [1,2] are one of the best systems for studying quantum tunneling of large moments [3]. Each molecule functions as a nanoscale, single-domain magnetic particle that, below its blocking temperature, exhibits the classical macroscale property of a magnet, namely magnetization hysteresis. Such a molecule straddles the classical/quantum interface in also displaying quantum tunneling of magnetization [4,5,6,7,8,9,10] and quantum phase interference [11,12,13]. A quantitative understanding of the mechanism of magnetization tunneling is being developed. For example, the width of tunnel transitions are in general larger than expected from dipolar interactions. Crystal defects may play an important role: loss or disorder of solvent molecules, and even dislocations have been proposed [14].Since SMMs occur as assemblies in crystals, there is the possibility of a small electronic interaction of adjacent molecules. This leads to very small superexchange interactions (or exchange interactions, for short) that depend strongly on the distance and the non-magnetic atoms in the exchange pathway. Up to now, such an intermolecular exchange interaction has been assumed to be negligibly small. However, our recent studies on several SMMs suggest that in most SMMs exchange interactions lead to a significant influence on the tunnel process. Recently, this intermolecular exchange interaction was used to couple antiferromagnetically two SMMs, each acting as a bias on its neighbor, resulting in quantum behavior different from that of individual SMMs [15].The main difference between dipole and exchange interactions are: (i) dipole interactions are long range whereas exchange interactions are usually short range; (ii) exchange interactions can be much stronger than dipolar interactions; (iii) whereas the sign of a dipolar interaction can be determined easily, that of exchange depends strongly on electronic details and is very difficult to predict; and (iv) dipolar interactions depend strongly on the spin ground state S, whereas exchange interactions depend strongly on the single-ion spin states. For example, intermolecular dipolar interactions can be neglected for antiferromagnetic SMMs with S = 0, whereas intermolecular exchange interactions can still be important and act as a source of decoherence.In this letter we show that dipolar and/or exchange interactions can lead to collective quantum processes. The one-body tunnel picture...

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The molecular approach to nanoscale magnetism

Cited by 210 publications

References 66 publications

Quantum description of spin tunneling in magnetic molecules

Quantum description of spin tunneling in magnetic molecules

Films of Mn12-acetate by pulsed laser evaporation

Spin-Spin Cross Relaxation in Single-Molecule Magnets

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