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Journal ArticleDOI

Langevin-dynamics study of the dynamical properties of small magnetic particles

J. L. García-Palacios, +1 more
- 01 Dec 1998 - 
- Vol. 58, Iss: 22, pp 14937-14958
TLDR
In this paper, the Langevin-dynamics approach was used to study the dynamics of magnetic nanoparticles, and the results were compared with different analytical expressions used to model the relaxation of nanoparticle ensembles, assessing their accuracy.
Abstract
The stochastic Landau-Lifshitz-Gilbert equation of motion for a classical magnetic moment is numerically solved (properly observing the customary interpretation of it as a Stratonovich stochastic differential equation), in order to study the dynamics of magnetic nanoparticles. The corresponding Langevin-dynamics approach allows for the study of the fluctuating trajectories of individual magnetic moments, where we have encountered remarkable phenomena in the overbarrier rotation process, such as crossing-back or multiple crossing of the potential barrier, rooted in the gyromagnetic nature of the system. Concerning averaged quantities, we study the linear dynamic response of the archetypal ensemble of noninteracting classical magnetic moments with axially symmetric magnetic anisotropy. The results are compared with different analytical expressions used to model the relaxation of nanoparticle ensembles, assessing their accuracy. It has been found that, among a number of heuristic expressions for the linear dynamic susceptibility, only the simple formula proposed by Shliomis and Stepanov matches the coarse features of the susceptibility reasonably. By comparing the numerical results with the asymptotic formula of Storonkin {Sov. Phys. Crystallogr. 30, 489 (1985) [Kristallografiya 30, 841 (1985)]}, the effects of the intra-potential-well relaxation modes on the low-temperature longitudinal dynamic response have been assessed, showing their relatively small reflection in the susceptibility curves but their dramatic influence on the phase shifts. Comparison of the numerical results with the exact zero-damping expression for the transverse susceptibility by Garanin, Ishchenko, and Panina {Theor. Math. Phys. (USSR) 82, 169 (1990) [Teor. Mat. Fiz. 82, 242 (1990)]}, reveals a sizable contribution of the spread of the precession frequencies of the magnetic moment in the anisotropy field to the dynamic response at intermediate-to-high temperatures.

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Citations
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Dispersion medium crystallization effect on the magnetic susceptibility of ferrofluids

TL;DR: In this article , it was shown that the formation of regions of high concentrations of dispersed phase particles during crystallization is the cause for a jump in colloid magnetic susceptibility, which refutes the previously existing opinion that the reason for the jump in the susceptibility of a ferrofluid at the temperature of transition to a solid state is the blocking of Brownian degrees of freedom of particles.
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Training of Quantized Deep Neural Networks using a Magnetic Tunnel Junction-Based Synapse

TL;DR: In this article, a hardware synapse circuit that uses the magnetic tunnel junction (MTJ) stochastic behavior to support the quantized update was proposed, which enables processing near memory (PNM) of QNN training.
Journal ArticleDOI

Machine learning nonequilibrium electron forces for spin dynamics of itinerant magnets

TL;DR: In this article , a generalized potential theory for conservative and non-conservative forces for the Landau-Lifshitz magnetization dynamics is presented, which makes possible an elegant generalization of the Behler-Parrinello machine learning approach, which is a cornerstone of ML-based quantum molecular dynamics methods, to the modeling of force fields in adiabatic spin dynamics of out-of-equilibrium itinerant magnetic systems.
Journal ArticleDOI

Dynamics of particles with cubic magnetic anisotropy in a viscous liquid

TL;DR: In this paper , the specific absorption rate (SAR) of a dilute assembly of spherical iron nanoparticles with cubic anisotropy distributed in a viscous liquid is calculated using the solution of stochastic Landau- Lifshitz equation for unit magnetization vector and stochastically equations for multiple particle directors that specify the spatial orientation of the nanoparticle in a liquid.
References
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Book

Stochastic processes in physics and chemistry

TL;DR: In this article, the authors introduce the Fokker-planck equation, the Langevin approach, and the diffusion type of the master equation, as well as the statistics of jump events.

Stochastic Processes in Physics and Chemistry

Abstract: Preface to the first edition. Preface to the second edition. Abbreviated references. I. Stochastic variables. II. Random events. III. Stochastic processes. IV. Markov processes. V. The master equation. VI. One-step processes. VII. Chemical reactions. VIII. The Fokker-Planck equation. IX. The Langevin approach. X. The expansion of the master equation. XI. The diffusion type. XII. First-passage problems. XIII. Unstable systems. XIV. Fluctuations in continuous systems. XV. The statistics of jump events. XVI. Stochastic differential equations. XVII. Stochastic behavior of quantum systems.
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TL;DR: In this article, a time-discrete approximation of deterministic Differential Equations is proposed for the stochastic calculus, based on Strong Taylor Expansions and Strong Taylor Approximations.
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The Fokker-Planck equation

Hannes Risken