Tunneling in Mesoscopic Magnetic Molecules

Politi, Paolo; Rettori, A.; Hartmann‐Boutron, F.; Villain, Jacques

doi:10.1103/physrevlett.75.537

Cited by 148 publications

(141 citation statements)

References 12 publications

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“…In the last years evidence of spin tunneling has been reported in M n 12 molecular complexes having very weakly interacting magnetic entities of spin Sϭ10. [14][15][16][17] The system is uniaxial with high accuracy. The reported anisotropy field is very high, H a ϳ10 T. This makes it a good candidate for the experimental study suggested above, though we cannot guarantee our theory to work well for the spin as low as 10.…”

Section: Conclusion and Suggestions For Experimentsmentioning

confidence: 99%

“…The influence of these interactions on the tunneling rate can be noticeable [5][6][7][8][9] but, apparently, does not kill the effect. Experiments have been reported [10][11][12][13][14][15][16][17] which indicated the possible presence of magnetic tunneling in small particles and in large magnetic molecules. Applications of this phenomenon have been discussed which include the reliability of small magnetic units in memory devices and their use in quantum computers.…”

Section: Introductionmentioning

confidence: 99%

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Quantum decay of metastable states in small magnetic particles

Miguel

Chudnovsky

1996

Phys. Rev. B

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We present an imaginary-time path-integral study of the problem of quantum decay of a metastable state of a uniaxial magnetic particle placed in the magnetic field at an arbitrary angle. Our findings agree with earlier results of Zaslavskii obtained by mapping the spin Hamiltonian onto a particle Hamiltonian. In the limit of low barrier, weak dependence of the decay rate on the angle is found, except for the field which is almost normal to the anisotropy axis, where the rate is sharply peaked, and for the field approaching the parallel orientation, where the rate rapidly goes to zero. This distinct angular dependence, together with the dependence of the rate on the field strength, provides an independent test for macroscopic spin tunneling. ͓S0163-1829͑96͒05625-1͔

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Section: Conclusion and Suggestions For Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantum decay of metastable states in small magnetic particles

Miguel

Chudnovsky

1996

Phys. Rev. B

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“…Though a number of efforts have been made to understand the energetics of the Mn 12 system, a quantitative theory is still lacking. Recent prospective Hamiltonians include anisotropy, Zeeman splitting, spin-phonon interaction, and transverse terms, as well as spin operators up to fourth order [5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Magnetic field effects on the far-infrared absorption inMn12-acetate

et al. 2001

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We report the far-infrared spectra of the molecular nanomagnet Mn12-acetate (Mn12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn12 molecule centered at 284, 306 and 409 cm −1 show changes with applied magnetic field. The structure near 284 cm −1 displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.

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“…For decoherence the most important coupling to S is the nondiagonal coupling ∼ SΩ o |q| to acoustic phonons having a Debye energy θ D (for a simple derivation of this see ref. [18], and for a thorough discussion of spin-phonon couplings see [32,48]). Standard spin-boson methods [1,6], applied to this coupling, give a contribution γ ph φ to γ φ of perturbative (ie., golden rule) form; when the applied bias is zero one gets [18]:…”

Section: B: Decoherence Ratesmentioning

confidence: 99%

Crossovers in spin-boson and central spin models

Stamp

Tupitsyn

2004

Chemical Physics

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We discuss how the crossovers in models like spin-boson model are changed by adding the coupling of the central spin to localised modes-the latter modelled as a 'spin bath'. These modes contain most of the environmental entropy and energy at low T in solid-state systems. We find that the low T crossover between oscillator bath and spin bath dominated decoherence, occurring as one reduces the energy scale of the central spin, is characterised by very low decoherence-we show how this works out in practise in magnetic insulators. We then reconsider the standard quantum-classical crossover in the dynamics of a tunneling system, including both spin and oscillator baths. It is found that the general effect of the spin bath is to broaden the crossover in temperature between the quantum and classical activated regimes. The example of tunneling nanomagnets is used to illustrate this. The oscillator bath models assume that each bath mode is weakly perturbed, and then the description of the bath by oscillators is well known to be correct. Many physical systems are very accurately described by such models [1,3,4,6], and they are central to much of reaction rate chemistry as well. Typically one studies either a particle tunneling from a trapped state to an open continuum of states (the dissipative tunneling problem), or a doublewell system in which a particle has to go from one well to another (the dissipative 2-well problem). One has a range of temperatures in which both activation and tunneling processes are important. Both the width of the crossover regime and the detailed dependence of transition rates, as a function of temperature and applied bias, are of interest [1,5]. In the 2 well problem, the 'quantum limit', where only the 2 lowest levels of the 2-well system are relevant (assuming a weak bias between the wells), has been studied very extensively. This is the 'spin-boson model', in which a 2-level system couples to the oscillator environment.Another interesting application of the spin-boson model is to the problem of qubits in quantum information processing (QUIP). The central issue here is the study of decoherence in the dynamics of the qubit, and how it depends on both simple things like applied fields, temperature, etc., and in a more complex way on the de-

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Tunneling in Mesoscopic Magnetic Molecules

Cited by 148 publications

References 12 publications

Quantum decay of metastable states in small magnetic particles

Quantum decay of metastable states in small magnetic particles

Magnetic field effects on the far-infrared absorption inMn12-acetate

Crossovers in spin-boson and central spin models

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