Effects of boundary conditions on magnetization switching in kinetic Ising models of nanoscale ferromagnets

Richards, Howard L.; Kolesík, M.; Lindgård, Per‐Anker; Rikvold, Per Arne; Novotny, M. A.

doi:10.1103/physrevb.55.11521

Cited by 50 publications

(37 citation statements)

References 113 publications

(142 reference statements)

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“…Together with ultrathin films, they are of interest as potential materials for ultra-high density recording media. The dynamics of magnetization reversal in nanoscale systems has been modeled by kinetic Ising systems subject to sudden field reversal [26][27][28][29][30][31]. These numerical and analytical studies give results in qualitative agreement with the experiments mentioned above.…”

Section: Introductionsupporting

confidence: 64%

Kinetic Ising model in an oscillating field: Avrami theory for the hysteretic response and finite-size scaling for the dynamic phase transition

1999

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Hysteresis is studied for a two-dimensional, spin-1/2, nearest-neighbor, kinetic Ising ferromagnet in a sinusoidally oscillating field, using Monte Carlo simulations and analytical theory. Attention is focused on large systems and moderately strong field amplitudes at a temperature below Tc. In this parameter regime, the magnetization switches through random nucleation and subsequent growth of many droplets of spins aligned with the applied field. Using a time-dependent extension of the Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory of metastable decay, we analyze the statistical properties of the hysteresis-loop area and the correlation between the magnetization and the field. This analysis enables us to accurately predict the results of extensive Monte Carlo simulations. The average loop area exhibits an extremely slow approach to an asymptotic, logarithmic dependence on the product of the amplitude and the field frequency. This may explain the inconsistent exponent estimates reported in previous attempts to fit experimental and numerical data for the low-frequency behavior of this quantity to a power law. At higher frequencies we observe a dynamic phase transition. Applying standard finite-size scaling techniques from the theory of second-order equilibrium phase transitions to this nonequilibrium transition, we obtain estimates for the transition frequency and the critical exponents (β/ν ≈ 0.11, γ/ν ≈ 1.84 and ν ≈ 1.1). In addition to their significance for the interpretation of recent experiments on switching in ferromagnetic and ferroelectric nanoparticles and thin films, our results provide evidence for the relevance of universality and finite-size scaling to dynamic phase transitions in spatially extended nonstationary systems. PACS number(s): 05.40.+j, 77.80.Dj, 64.60.Qb

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Section: Introductionsupporting

confidence: 64%

Kinetic Ising model in an oscillating field: Avrami theory for the hysteretic response and finite-size scaling for the dynamic phase transition

1999

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“…They call this the "single-droplet region", meaning that the nucleation of the stable state is achieved via the formation of a single cricical droplet, see also [RKLRN,TM2] In Fig. 3 we have plotted our numerical measurements of the escape time τ β versus the inverse of the magnetic field.…”

Section: Numerical Resultsmentioning

confidence: 99%

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Cirillo

Lebowitz

1998

Journal of Statistical Physics

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We investigate metastability in the two dimensional Ising model in a square with free boundary conditions at low temperatures. Starting with all spins down in a small positive magnetic field, we show that the exit from this metastable phase occurs via the nucleation of a critical droplet in one of the four corners of the system. We compute the lifetime of the metastable phase analytically in the limit T → 0, h → 0 and via Monte Carlo simulations at fixed values of T and h and find good agreement. This system models the effects of boundary domains in magnetic storage systems exiting from a metastable phase when a small external field is applied.

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“…Because each time only one Ising lattice is selected, the change of the energy due to the spin flip is obtained by updating either H 0 or H 1 in Eq. (19).…”

Section: Appendix Amentioning

confidence: 99%

Simulation of magnetization switching in biaxial single-domain ferromagnetic particles

2000

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The magnetization switching dynamics of biaxial single-domain homogeneous ferromagnetic particles, in which the two easy axes are perpendicular to each other, is simulated using a 4-state clock model. A zero-field mapping of the statics between the symmetric 4-state clock model and two decoupled Ising models is extended to non-zero field statics and to the dynamics. This significantly simplifies the analysis of the simulation results. We measure the magnetization switching time of the model and analyze the results using droplet theory. The switching dynamics in the asymmetric model is more complicated. If the easy axis is perpendicular to the stable magnetization direction, the system can switch its magnetization via two different channels, one very fast and the other very slow. A maximum value for the switching field as a function of system size is obtained. The asymmetry affects the switching fields differently, depending on whether the switching involves one single droplet or many droplets of spins in the stable magnetization configuration. The angular dependence of the switching field in symmetric and asymmetric models is also studied. PACS Number(s): 75.40. Mg, 05.50.+q, 02.70.Lq,

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Effects of boundary conditions on magnetization switching in kinetic Ising models of nanoscale ferromagnets

Cited by 50 publications

References 113 publications

Kinetic Ising model in an oscillating field: Avrami theory for the hysteretic response and finite-size scaling for the dynamic phase transition

Kinetic Ising model in an oscillating field: Avrami theory for the hysteretic response and finite-size scaling for the dynamic phase transition

Untitled

Simulation of magnetization switching in biaxial single-domain ferromagnetic particles

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