Spectral-density method for classical systems: Heisenberg ferromagnet

Campana, L. S.; D'Auria, A. Caramico; D'Ambrosio, M.; Esposito, U.; Cesare, L. De; Kamieniarz, G.

doi:10.1103/physrevb.30.2769

Cited by 24 publications

(63 citation statements)

References 22 publications

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“…temperature), we employ the classical spectral density method (CSDM) for spinwaves [41,42], previously shown to have a good agreement with the Langevin simulations in simple cubic lattice materials and FePt [42,45]. The method is based on the use of Green's functions in reciprocal space which first leads to an infinite set of coupled equations for thermally averaged moments of all orders.…”

Section: B Exchange Stiffness: Analytical Approachmentioning

confidence: 99%

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Temperature-dependent exchange stiffness and domain wall width in Co

et al. 2016

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The micromagnetic exchange stiffness is a critical parameter in numerical modeling of magnetization dynamics and reversal processes, yet the current literature reports a wide range of values even for such simple and widely used material as Cobalt.With use of ab-intio estimated Heisenberg parameters we calculate the low temperature micromagnetic exchange stiffness parameters for hexagonal-close-packed (HCP) and face-centred cubic Cobalt without previous and our own. For HCP Co they are slightly different in the directions parallel and perpendicular to the c-axis. We establish the exchange stiffness scaling relation with magnetization A(m) ∼ m 1.8 valid for all sets of parameters for a wide range of temperatures. For HCP Co we find an anisotropic domain wall width in the range 24 − 29 nm which increases slowly with temperature. The results form a critical input for large-scale temperature-dependent micromagnetics simulations and demonstrate the importance of correct parameterization for accurate simulation of magnetization dynamics.

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Section: B Exchange Stiffness: Analytical Approachmentioning

confidence: 99%

“…The spectral density is assumed to be a delta-function. The following decoupling scheme which leaves the equations for the first two moments only (found to be sufficient for the exchange interactions [41,42]) is then assumed…”

Section: B Exchange Stiffness: Analytical Approachmentioning

confidence: 99%

Temperature-dependent exchange stiffness and domain wall width in Co

et al. 2016

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“…[68,70,71]. The exchange constants are chosen to reproduce the bulk Curie temperatures using the classical spectral density method [72]. The magnetocrystalline anisotropy energy density is given by e MCA = K 1 …”

Section: A Atomic Level Simulation Of Magnetocrystalline and Effectimentioning

confidence: 99%

Direct observation of enhanced magnetism in individual size- and shape-selected 3d transition metal nanoparticles

et al. 2017

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Magnetic nanoparticles are critical building blocks for future technologies ranging from nanomedicine to spintronics. Many related applications require nanoparticles with tailored magnetic properties. However, despite significant efforts undertaken towards this goal, a broad and poorly understood dispersion of magnetic properties is reported, even within monodisperse samples of the canonical ferromagnetic 3d transition metals. We address this issue by investigating the magnetism of a large number of size-and shape-selected, individual nanoparticles of Fe, Co, and Ni using a unique set of complementary characterization techniques. At room temperature, only superparamagnetic behavior is observed in our experiments for all Ni nanoparticles within the investigated sizes, which range from 8 to 20 nm. However, Fe and Co nanoparticles can exist in two distinct magnetic states at any size in this range: (i) a superparamagnetic state, as expected from the bulk and surface anisotropies known for the respective materials and as observed for Ni, and (ii) a state with unexpected stable magnetization at room temperature. This striking state is assigned to significant modifications of the magnetic properties arising from metastable lattice defects in the core of the nanoparticles, as concluded by calculations and atomic structural characterization. Also related with the structural defects, we find that the magnetic state of Fe and Co nanoparticles can be tuned by thermal treatment enabling one to tailor their magnetic properties for applications. This paper demonstrates the importance of complementary single particle investigations for a better understanding of nanoparticle magnetism and for full exploration of their potential for applications.

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“…This description is related to the system geometry, so the term geometric frustration is commonly used in this case. In such systems competing interactions are present and such approach can be easily adopted to many classical and semi-classical models, for example, the Potts model or the classical counterpart of the Heisenberg model [4,5]. The presence of competing interactions means that a system cannot simultaneously satisfy all the interactions that it undergoes.…”

Section: Introductionmentioning

confidence: 99%

Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

et al. 2018

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Geometrically frustrated quantum spin systems, with competing antiferromagnetic couplings, show the Kahn degenerate frustration for some specific values of Heisenberg Hamiltonian parameters. It has been recently shown for rings with a defect bond and centered rings. In the case of classical counterparts of these systems, degenerated configurations with the lowest energy are present for the energy function parameter greater than a certain threshold. In these domains such configurations are planar but non-collinear with continuous changes of the net magnetic moment with respect to the Hamiltonian parameter. Outside these domains there is unique collinear ground state configuration (neglecting choice of the net magnetic moment direction). However, these collinear configurations are the same in both non-frustrated and geometrically frustrated domains. Numerically exact calculations for quantum systems strongly confirm that determined properties of their classical counterparts realize the classical limit s Ñ 8.

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Spectral-density method for classical systems: Heisenberg ferromagnet

Cited by 24 publications

References 22 publications

Temperature-dependent exchange stiffness and domain wall width in Co

Temperature-dependent exchange stiffness and domain wall width in Co

Direct observation of enhanced magnetism in individual size- and shape-selected 3d transition metal nanoparticles

Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

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