Thermal fluctuations in a pair of magnetostatically coupled particles

Lyberatos, A.; Chantrell, R.W.

doi:10.1063/1.352594

Cited by 94 publications

(76 citation statements)

References 5 publications

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“…Langevin dynamics for spins was developed in Refs. [18][19][20][21][22][23][24][25][26], and its application to a large system of interacting spins were considered in Refs. 9, 26 and 27.…”

Section: Introductionmentioning

confidence: 99%

Spin-lattice-electron dynamics simulations of magnetic materials

Dudarev

Woo

2012

Phys. Rev. B

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We develop a dynamic spin-lattice-electron model for simulating the time-dependent evolution of coupled spin, atomic, and electronic degrees of freedom in a magnetic material. Using the model, we relate the dissipative parameters entering the Langevin equations for the lattice and spin degrees of freedom to the heat transfer coefficients of a phenomenological spin-lattice-electron three-temperature model. We apply spin-lattice-electron dynamics simulations to the interpretation of experiments on laser-induced demagnetization of iron thin films, and estimate the rates of heat transfer between the spins and electrons, and between atoms and electrons. To model the dynamics of energy dissipation in a magnetic material undergoing plastic deformation, we develop an algorithm that separates the local collective modes of motion of atoms from their random thermal motion. Using this approach, we simulate the propagation of compressive shock waves through magnetic iron. We also explore the microscopic dynamics of dissipative coupling between the spin and lattice subsystems, and show that the rate of spin-lattice heat transfer is proportional to the integral of the four-spin time-dependent correlation function.

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“…Langevin dynamics for spins was developed in Refs. [18][19][20][21][22][23][24][25][26], and its application to a large system of interacting spins were considered in Refs. 9, 26 and 27.…”

Section: Introductionmentioning

confidence: 99%

Spin-lattice-electron dynamics simulations of magnetic materials

Dudarev

Woo

2012

Phys. Rev. B

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“…Numerical studies of the thermal activation in magnetic systems base either on Langevin dynamics [3][4][5][6] or on Monte Carlo methods. With the second method, mainly nucleation processes in Ising systems have been studied [7,8], but also vector spin models have been used to investigate the switching behavior in systems with continuous degrees of freedom [9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Magnetization switching in nanowires: Monte Carlo study with fast Fourier transformation for dipolar fields

Hinzke¹,

Nowak²

2000

Journal of Magnetism and Magnetic Materials

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For the investigations of thermally activated magnetization reversal in systems of classical magnetic moments numerical methods are desirable. We present numerical studies which base on time quantified Monte Carlo methods where the long-range dipole-dipole interaction is calculated with the aid of fast Fourier transformation. As an example, we study models for ferromagnetic nanowires comparing our numerical results for the characteristic time of the reversal process also with numerical data from Langevin dynamics simulations where the fast Fourier transformation method is well established. Depending on the system geometry different reversal mechanism occur like coherent rotation, nucleation, and curling.

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“…He also derived the Arrhenius-Néel formula to describe the relaxation rate in the axially symmetric case of single-domain particles which was lately generalized to the presence of external field [3,4]. Since the paper of Chantrell and Lyberatos [5], this Langevin-dynamics approach of Brown has been brought to numerical micromagnetics to model the thermal properties of an ensemble of interacting particles and, more generally, of ferromagnetic materials, interpreting the micromagnetic discretization elements as small particles. Generally speaking, the LL equation used in these simulations is a lowtemperature approximation only.…”

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confidence: 99%

Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures

2004

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We present numerical and analytical results for the swiching times of magnetic nanoparticles with uniaxial anisotropy at elevated temperatures, including the vicinity of Tc. The consideration is based in the Landau-Lifshitz-Bloch equation that includes the relaxation of the magnetization magnitude M . The resulting switching times are shorter than those following from the naive Landau-Lifshitz equation due to (i) additional barrier lowering because of the reduction of M at the barrier and (ii) critical divergence of the damping parameters.PACS numbers: 75.50. Tt, 75.40.Mg, 75.60.Nt, 75.50.Ss The theory of thermal fluctuations of small magnetic particles is one of the fundamental issues of modern micromagnetics. The conditions at which the particle becomes superparamagnetic define the thermal stability of the magnetized state and, therefore, is also valuable for technological application such as magnetic recording [1]. The basis of the theory has been introduced by Brown [2] who suggested to include thermal fluctuations into the Landau-Lifshitz (LL) dynamical equation as formal random fields whose properties are defined by the equilibrium solution of the correspondent Fokker-Planck (FP) equation. He also derived the Arrhenius-Néel formula to describe the relaxation rate in the axially symmetric case of single-domain particles which was lately generalized to the presence of external field [3,4]. Since the paper of Chantrell and Lyberatos [5], this Langevin-dynamics approach of Brown has been brought to numerical micromagnetics to model the thermal properties of an ensemble of interacting particles and, more generally, of ferromagnetic materials, interpreting the micromagnetic discretization elements as small particles. Generally speaking, the LL equation used in these simulations is a lowtemperature approximation only. Recently a generalized Landau-Lifshitz-Bloch (LLB) equation for a ferromagnet [6,8] was derived which is valid for all temperatures and includes the longitudinal relaxation. The deviations of the LLB dynamics from the LL dynamics should be pronounced at high temperatures, especially close to the Curie temperature T c . The validity of this approach has been confirmed by the measurements of the domain-wall mobility in crystals of Ba-and Sr-hexaferrites close to T c [9].Since the proposal of the heat-assisted magnetic recording (HAMR) [10] the problem of high-temperature thermal magnetization dynamics has become of large practical importance. The basic idea of HAMR is to write bits of information at elevated temperature (close to the Curie temperature, where the switching field is small) and store the information at room temperature. To achieve a significant areal density advantage, the use of high-anisotropy intermetallics such as Ll 0 FePt has been suggested [11]. Therefore, from both fundamental and applied points of view it is necessary to consider the micromagnetics of small particles (or magnetic grains) at elevated temperatures. The straightforward approach [12] uses the formalism of the sta...

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Thermal fluctuations in a pair of magnetostatically coupled particles

Cited by 94 publications

References 5 publications

Spin-lattice-electron dynamics simulations of magnetic materials

Spin-lattice-electron dynamics simulations of magnetic materials

Magnetization switching in nanowires: Monte Carlo study with fast Fourier transformation for dipolar fields

Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures

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