Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules

Prokof’ev, Nikolay; Stamp, P. C. E.

doi:10.1103/physrevlett.80.5794

Cited by 304 publications

(401 citation statements)

References 14 publications

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“…Hyperfine interactions enable spins to tunnel even when the ensuing Zeeman energy change 2ε h is much larger than the tunnel splitting energy ∆, provided | ε h | is smaller than some ε w . 5 For Fe 8 , for instance, ∆ ∼ 10 −4 mK, ε w ≈ 10 mK, and the rms value of the Zeeman energy δε h is approximately 400 mK. We shall restrict ourselves to systems with ε w ≪ δε h .…”

Section: Introductionmentioning

confidence: 99%

“…The time evolution of "holes" that, under suitable conditions, develop in a magnetization density function, have also been reported. 6,7 The existing theory at the time 5,8,9 predicted a universal √ t short time relaxation from a fully polarized system, but said little about relaxation from or into weakly polarized states. 10 Other theories 11 take hyperfine interactions into account but disregard dipole-dipole interactions.…”

Section: Introductionmentioning

confidence: 99%

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Time relaxation of interacting single-molecule magnets

Fernández

Alonso

2005

Phys. Rev. B

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We study the relaxation of interacting single-molecule magnets (SMMs) in both spatially ordered and disordered systems. The tunneling window is assumed to be, as in Fe 8 , much narrower than the dipolar field spread. We show that relaxation in disordered systems differs qualitatively from relaxation in fully occupied cubic and Fe 8 lattices. We also study how line shapes that develop in "hole-digging" experiments evolve with time t in these fully occupied lattices. We show (1) that the dipolar field h scales as t p in these hole line shapes and show (2) how p varies with lattice structure. Line shapes are not, in general, Lorentzian. More specifically, in the lower portion of the hole, they behave as (| h | /t p ) (1/p)−1 if h is outside the tunnel window. This is in agreement with experiment and with our own Monte Carlo results.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time relaxation of interacting single-molecule magnets

Fernández

Alonso

2005

Phys. Rev. B

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“…To give results comparable with experiment we have generalised the kinetic equation (37) to include dipolar interactions-this development is a rather messy but fairly straightforward adaptation of the method used in ref. [59]. The main effect of adding these interactions is however not to change the width of the crossover, but rather to change the time dependence of the relaxationthis it is fairly complex, even in the quantum regime [59], and not relevant to the present study.…”

Section: A: Quantum-classical Crossover For Magnetic Moleculesmentioning

confidence: 94%

“…[59]. The main effect of adding these interactions is however not to change the width of the crossover, but rather to change the time dependence of the relaxationthis it is fairly complex, even in the quantum regime [59], and not relevant to the present study. The most important point to be noted from Fig.…”

Section: A: Quantum-classical Crossover For Magnetic Moleculesmentioning

confidence: 94%

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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“…Magnetic clusters such as Mn 12 and Fe 8 are systems that can be described by metastable wells. Early relaxation experiments suggested escape from the wells by tunneling through a barrier 1,2 and energy-level quantization within a well.…”

Section: Introductionmentioning

confidence: 99%

Time-dependent heat capacity ofMn12clusters

et al. 1999

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In this paper we discuss both theoretical and experimental results on the time dependence of the heat capacity of oriented Mn 12 magnetic clusters when a magnetic field is applied along their easy axis. Our calculations are based on the existence of two contributions. The first one is associated with the thermal populations of the 21 different S z levels in the two potential wells of the magnetic uniaxial anisotropy and the second one is related to the transitions between the S z levels. We compare our theoretical predictions with experimental data on the heat capacity for different resolution times at different fields and temperatures.

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Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules

Cited by 304 publications

References 14 publications

Time relaxation of interacting single-molecule magnets

Time relaxation of interacting single-molecule magnets

Crossovers in spin-boson and central spin models

Time-dependent heat capacity ofMn12clusters

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