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Journal Articles Journal of Magnetism and Magnetic Materials Year : 2024

Micromagnetic simulations of the size dependence of the Curie temperature in ferromagnetic nanowires and nanolayers

Abstract

We solve the Landau-Lifshitz-Gilbert equation in the finite-temperature regime, where thermal fluctuations are modeled by a random magnetic field whose variance is proportional to the temperature. By rescaling the temperature proportionally to the computational cell size ∆x (T → T ∆x/a_{eff} , where a eff is the lattice constant) [M. B. Hahn, J. Phys. Comm., 3:075009, 2019], we obtain Curie temperatures T_C that are in line with the experimental values for cobalt, iron and nickel. For finite-sized objects such as nanowires (1D) and nanolayers (2D), the Curie temperature varies with the smallest size d of the system. We show that the difference between the computed finite-size T_C and the bulk T_C follows a power-law of the type: (ξ_0 /d)^{λ} , where ξ_0 is the correlation length at zero temperature, and λ is a critical exponent. We obtain values of ξ_0 in the nanometer range, also in accordance with other simulations and experiments. The computed critical exponent is close to λ = 2 for all considered materials and geometries. This is the expected result for a mean-field approach, but slightly larger than the values observed experimentally.
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Dates and versions

hal-04364178 , version 1 (28-12-2023)
hal-04364178 , version 2 (25-04-2024)

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Cite

Clémentine Courtès, Matthieu Boileau, Raphaël Côte, Paul Antoine Hervieux, Giovanni Manfredi. Micromagnetic simulations of the size dependence of the Curie temperature in ferromagnetic nanowires and nanolayers. Journal of Magnetism and Magnetic Materials, 2024, 598, pp.172040. ⟨10.1016/j.jmmm.2024.172040⟩. ⟨hal-04364178v2⟩
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