Non-equilibrium finite temperature dynamics of magnetic quantum systems: applications to spin-polarized scanning tunneling microscopy

Them, Kolja; Stapelfeldt, T.; Vedmedenko, E. Y.; Wiesendanger, R.

doi:10.1088/1367-2630/15/1/013009

Cited by 7 publications

(4 citation statements)

References 27 publications

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“…Mathematically, a SPIONs distribution is described as a spin system on a lattice L = Z d and the positions of the SPIONs corresponds to points x ∈ L in the lattice L (Them et al 2013, Them 2014a). In a quantum mechanical description one associates with each point x ∈ Z d a Hilbert space {H} x of dimension 2s(x) + 1.…”

Section: Quantum Mechanical Description Of Magnetic Nanoparticlesmentioning

confidence: 99%

On magnetic dipole–dipole interactions of nanoparticles in magnetic particle imaging

Them

2017

Phys. Med. Biol.

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Magnetic dipole-dipole (MDD) interactions between iron oxide nanoparticles can influence the sensitivity, image resolution and quantification of magnetic particle imaging (MPI). For the first time, the Landau-Lifshitz-Gilbert equation (LLG) for MDD interactions has been solved to investigate the effect of MDD interactions on the MPI spectrum. It was found that at concentrations above 39 mmol(Fe) l, MDD interactions significantly influence MPI spectra. This influence increases with increasing harmonics, which means first harmonics should be preferred for iron quantification. Since ≈10 particles are neglected in the LLG compared to in an MPI experiment, the calculated limit below which MDD interactions can be neglected is only a bound. The true limit is therefore below the calculated limit of 39 mmol(Fe) l, because all other neglected particles also contribute to deviations in the MPI spectra via MDD interactions. Therefore, a quantum mechanical bound on the influence of MDD interactions is calculated, including up to 10 particles. Analysis of the bound as a function of the particle number provides a valuable insight into the influence of the large number of particles neglected in numerical simulations. Both results are compared with concentrations in biomedical MPI experiments. We conclude that the standard approximation of an absence of MDD interactions in MPI experiments must be handled more carefully. Our method of incorporating MDD interactions into the LLG can be easily implemented as part of model-based reconstruction to increase the sensitivity, image resolution and quantitative tracer detection during MPI.

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Section: Quantum Mechanical Description Of Magnetic Nanoparticlesmentioning

confidence: 99%

On magnetic dipole–dipole interactions of nanoparticles in magnetic particle imaging

Them

2017

Phys. Med. Biol.

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“…Hence, the magnetization of the output atom is controlled via the magnetization of the cobalt islands, which are switched with external magnetic field pulses. Experimental data [9] as well as theoretical results [10] indicate that the readout of a single atom magnetization state is sufficiently described by a KMS state, which is identical to the thermal equilibrium Gibbs state for finite dimensional systems [11].…”

Section: Magnetic Interactions and The Spintronic Logic Devicementioning

confidence: 80%

Bounds on expectation values of quantum subsystems and perturbation theory

Them¹,

Vedmedenko²,

Fredenhagen³

et al. 2015

J. Phys. A: Math. Theor.

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The numerical investigation of many-body quantum systems usually requires different kinds of physical approximations. The error which is made by these approximations is difficult to estimate and remains unknown in most cases. We examine an upper bound on expectation values of quantum subsystems, which enables the estimation of the maximum error that is made by physical approximations outside the subsystem. This is of special interest for perturbation theory, where the bath is commonly approximated with simplified interactions. A recently realized all-spin-based atomic-scale logic device, consisting of iron atoms and cobalt islands placed on a copper substrate, serves as a specific example for an application of the bound. Strength and weakness of these methods are critically discussed and we provide a quantitative answer to the old question in which cases a small quantum system can be used instead of a large one.

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“…This symmetry breaking promotes the spontaneous transition of magnetization from one energy well (expectation value of magnetization) to another one under the energy barrier, known as the resonant quantum tunneling of magnetization (MQT). The MQT have been measured in many solid state and molecular magnetic systems and is of large technological importance [22,23,27,29,31], because it is directly connected to the life-times of the information bits. In zero external magnetic field =  B 0 z , the quantum mechanical levels =  m s have the lowest energy.…”

Section: Quasi-quantum Revival and Magnetization Tunnelingmentioning

confidence: 99%

“…Particularly, quantum mechanical tunneling or the non-classical field dependence of magnetization has been reported for nano-magnets [20], molecules [21,22] and single atoms [23]. Therefore, instead of studies of timeaveraged properties like, e.g., magnetization curves [23,24], nowadays the emphasis is put on the time dependent behavior of magnetization [25][26][27][28][29]. This trend is promoted further by the development of novel pump-probe techniques [30] allowing for the sub-femto-second time resolution of magnetization dynamics, which might shed light on the revival phenomena in nano-magnetic systems.…”

Section: Introductionmentioning

confidence: 99%

Quantum revivals and magnetization tunneling in effective spin systems

et al. 2016

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Quantum mechanical objects or nano-objects have been proposed as bits for information storage. While time-averaged properties of magnetic, quantum-mechanical particles have been extensively studied experimentally and theoretically, experimental investigations of the real time evolution of magnetization in the quantum regime were not possible until recent developments in pump-probe techniques. Here we investigate the quantum dynamics of effective spin systems by means of analytical and numerical treatments. Particular attention is paid to the quantum revival time and its relation to the magnetization tunneling. The quantum revival time has been initially defined as the recurrence time of a total wave-function. Here we show that the quantum revivals of wave-functions and expectation values in spin systems may be quite different which gives rise to a more sophisticated definition of the quantum revival within the realm of experimental research. Particularly, the revival times for integer spins coincide which is not the case for half-integer spins. Furthermore, the quantum revival is found to be shortest for integer ratios between the on-site anisotropy and an external magnetic field paving the way to novel methods of anisotropy measurements. We show that the quantum tunneling of magnetization at avoided level crossing is coherent to the quantum revival time of expectation values, leading to a connection between these two fundamental properties of quantum mechanical spins.

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Non-equilibrium finite temperature dynamics of magnetic quantum systems: applications to spin-polarized scanning tunneling microscopy

Cited by 7 publications

References 27 publications

On magnetic dipole–dipole interactions of nanoparticles in magnetic particle imaging

On magnetic dipole–dipole interactions of nanoparticles in magnetic particle imaging

Bounds on expectation values of quantum subsystems and perturbation theory

Quantum revivals and magnetization tunneling in effective spin systems

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