Thermal diffusion in the system 20neon - methane

Acharyya, S.; Datta, K. K.

doi:10.1088/0022-3727/4/1/311

Cited by 4 publications

(4 citation statements)

References 8 publications

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“…It agrees fairly well with the MC estimated phase diagram in the low h p (i.e. large ∆t) limit [4,8]. For large values of h p , the critical droplet size l c ∼ 1/h p being much smaller than the system size L, many droplets grow simultaneously and the transition occurs due to coalescence of the droplets and not by the above-mentioned process of growth of a single droplet.…”

Section: Monte Carlo Studysupporting

confidence: 85%

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Dynamic magnetization-reversal transition in the Ising model

Misra

Chakrabarti

1998

Phys. Rev. E

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We report the results of mean field and the Monte Carlo study of the dynamic magnetization-reversal transition in the Ising model, brought about by the application of an external field pulse applied in opposition to the existing order before the application of the pulse. The parameters controlling the transition are the strength h p and the duration ⌬t of the pulse. In the mean field case, an approximate analytical expression is obtained for the phase boundary which agrees well with that obtained numerically in the small ⌬t and large T limit. The order parameter of the transition has been identified, and is observed to vary continuously near the transition. The order parameter exponent ␤ was estimated both for the mean field (␤ϭ1) and the Monte Carlo (␤ϭ0.90Ϯ0.02 in two dimensions͒ cases. The transition shows a ''critical slowing down'' type behavior near the phase boundary with diverging relaxation time. The divergence was found to be logarithmic in the mean field case and exponential in the Monte Carlo case. The finite size scaling technique was employed to estimate the correlation length exponent (ϭ1.5Ϯ0.3 in two dimensions͒ in the Monte Carlo case.

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Section: Monte Carlo Studysupporting

confidence: 85%

“…Typical number of initial seed values taken to generate the configurations over which each data point is averaged is 500. The variation of O was again fitted to the power law form (8) with the order parameter exponent β and we find β ∼ 1 by fitting the MC results for four different values of ∆t and four different values of T .…”

Section: Monte Carlo Studymentioning

confidence: 99%

Dynamic magnetization-reversal transition in the Ising model

Misra

Chakrabarti

1998

Phys. Rev. E

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“…Especially, the general result that the effective energy barriers for single-and multidroplet nucleation are related by the D−dependent factor is confirmed. A corresponding behavior concerning the field dependence of the the metastable lifetime was also observed recently [15,16].…”

supporting

confidence: 71%

“…This reversal process occurs when the probability for the growth of large droplets is high enough and when the critical droplet size is smaller than the system size so that many droplets may occur in the system at the same time. This is the case for higher fields or larger temperatures [15,16] . The lifetime for the multi-droplet nucleation in D-dimensions is [14] τ ∼ exp ∆E n (D + 1)T .…”

mentioning

confidence: 89%

Magnetization switching in small ferromagnetic particles: Nucleation and coherent rotation

Nowak¹,

Hinzke²

1999

Journal of Applied Physics

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The mechanisms of thermally activated magnetization switching in small ferromagnetic particles driven by an external magnetic field are investigated. For low uniaxial anisotropy the spins rotate coherently while for sufficiently large uniaxial anisotropy they behave Ising-like, i. e. the switching then is due to nucleation. The crossover from coherent rotation to nucleation is studied for the classical threedimensional Heisenberg model with uniaxial anisotropy by Monte Carlo simulations. From the temperature dependence of the metastable lifetime the energy barrier of a switching process can be determined. For the case of infinite anisotropy we compare numerical results from simulations of the Ising model with theoretical results for energy barriers for both, single-droplet and multi-droplet nucleation. The simulated barriers are in agreement with the theoretical predictions.With decreasing size ferromagnetic particles become single-domain which improves their quality for magnetic recording. On the other hand, when the particles are too small they become superparamagnetic and then due to thermal fluctuations no magnetic information can be stored (see e. g. [1] for a review). Hence, much effort has been devoted to an understanding of the behavior of small magnetic particles experimentally [2-4], analytically [5], and in computer simulations. In the latter case, mainly magnetization switching by nucleation [6][7][8] has been studied using Ising models of finite size, but also other reversal mechanisms in models with continuous degrees of freedom like coherent rotation, single-droplet nucleation, and multi-droplet nucleation have been discussed [9,8].In this paper we focus on different thermally activated reversal mechanisms occuring in ferromagnetic particles. We will consider a finite, spherical, three-dimensional system of magnetic moments. These magnetic moments may represent atomic spins or also block spins following from a coarse graining of the physical lattice [10]. Our system is defined by a classical Heisenberg Hamiltonian,where the S i are three dimensional vectors of unit length. The first sum which represents the exchange of the spins is over nearest neighbors with the exchange coupling constant J. The second sum represents an uniaxial anisotropy which favors the z-axis as easy axis (anisotropy constant d > 0). The last sum is the coupling of the spins to an applied magnetic field, where B is the strength of the field times the absolute value of the magnetic moment of the spin. We neglect the dipolar interaction. Therefore, the validity of our results is restricted to particles which are small enough to be single-domain in the remanent state [11]. In the following we will investigate the thermally activated reversal of the magnetization of a particle which is destabilized by a magnetic field pointing into the direction antiparallel to the initial magnetization which is parallel to the easy axis of the system initially. In this case after some time the particle will reverse its magnetization.Due to the m...

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Réalisation et études des couches minces évaporées de SnSe2

Quan

Fèvre

1982

Thin Solid Films

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Thermal diffusion in the system 20neon - methane

Cited by 4 publications

References 8 publications

Dynamic magnetization-reversal transition in the Ising model

Dynamic magnetization-reversal transition in the Ising model

Magnetization switching in small ferromagnetic particles: Nucleation and coherent rotation

Réalisation et études des couches minces évaporées de SnSe2

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