Temperature-dependent exchange stiffness and domain wall width in Co

Moreno, R.; Evans, Richard F. L.; Khmelevskyi, Sergii; Muñoz, M. C.; Chantrell, R.W.; Chubykalo‐Fesenko, O.

doi:10.1103/physrevb.94.104433

Cited by 98 publications

(79 citation statements)

References 45 publications

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“…5(d). This is different from the low-temperature power-law scaling behavior of m −0.59 as found in cobalt [60], possibly due to the complicated and intrinsically different crystal structure of Nd 2 Fe 14 B.…”

Section: Domain Wallcontrasting

confidence: 78%

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Gong

Evans

et al. 2019

Phys. Rev. B

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Temperature-dependent magnetic properties of Nd2Fe14B permanent magnets, i.e., saturation magnetization Ms(T ), effective magnetic anisotropy constants K eff i (T ) (i = 1, 2, 3), domain wall width δw(T ), and exchange stiffness constant Ae(T ), are calculated by using ab-initio informed atomistic spin model simulations. We construct the atomistic spin model Hamiltonian for Nd2Fe14B by using the Heisenberg exchange of Fe−Fe and Fe−Nd atomic pairs, the uniaxial single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions which is approximately expanded into an energy formula featured by second, fourth, and sixth-order phenomenological anisotropy constants. After applying a temperature rescaling strategy, we show that the calculated Curie temperature, spin-reorientation phenomenon, Ms(T ), δw(T ), and K eff i (T ) agree well with the experimental results. Ae(T ) is estimated through a general continuum description of the domain wall profile by mapping atomistic magnetic moments to the macroscopic magnetization. Ae is found to decrease more slowly than K eff 1 with increasing temperature, and approximately scale with normalized magnetization as Ae(T ) ∼ m 1.2 . Especially, the possible domain wall configurations at temperatures below the spin-reorientation temperature and the associated δw and Ae are identified. This work provokes a scale bridge between ab-initio calculations and temperature-dependent micromagnetic simulations of Nd-Fe-B permanent magnets.

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Section: Domain Wallcontrasting

confidence: 78%

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Gong

Evans

et al. 2019

Phys. Rev. B

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“…is therefore a better metric to use to compare samples with different saturation magnetizations. The difference between the exchange length from this study of λ ex = 9.7 nm and the previously reported value of 21 nm 20 could be due to differences in grain structure between the patterned and unpatterned films 44 as well as difficulty in mode assignment, n, in prior work where fewer modes are visible.…”

contrasting

confidence: 83%

Low-damping ferromagnetic resonance in electron-beam patterned, high-Q vanadium tetracyanoethylene magnon cavities

et al. 2019

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Integrating patterned, low-loss magnetic materials into microwave devices and circuits presents many challenges due to the specific conditions that are required to grow ferrite materials, driving the need for flip-chip and other indirect fabrication techniques. The low-loss (α = (3.98 ± 0.22) × 10 −5 ), room-temperature ferrimagnetic coordination compound vanadium tetracyanoethylene (V[TCNE] x ) is a promising new material for these applications that is potentially compatible with semiconductor processing. Here we present the deposition, patterning, and characterization of V[TCNE] x thin films with lateral dimensions ranging from 1 micron to several millimeters. We employ electron-beam lithography and liftoff using an aluminum encapsulated poly(methyl methacrylate), poly(methyl methacrylate-methacrylic acid) copolymer bilayer (PMMA/P(MMA-MAA)) on sapphire and silicon. This process can be trivially extended to other common semiconductor substrates. Films patterned via this method maintain low-loss characteristics down to 25 microns with only a factor of 2 increase down to 5 microns. A rich structure of thickness and radially confined spin-wave modes reveals the quality of the patterned films. Further fitting, simulation, and analytic analysis provides an exchange stiffness, A ex = (2.2 ± 0.5) × 10 −10 erg/cm, as well as insights into the mode character and surface spin pinning. Below a micron, the deposition is non-conformal, which leads to interesting and potentially useful changes in morphology. This work establishes the versatility of V[TCNE] x for applications requiring highly coherent magnetic excitations ranging from microwave communication to quantum information. arXiv:1910.05325v1 [physics.app-ph]

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“…Under a mean field approximation with homogeneous spin systems, the exponent n is 2 [30,46]. However, under more accurate methods, the exponent takes a value different from 2, for example, FePt: n = 1.76 [30], hcp-Co: n = 1.79 [31]. Thus we estimate n to examine the thermal properties for the Nd 2 Fe 14 B, by fitting A(T ) in Fig.…”

Section: B Exchange Stiffness Constantmentioning

confidence: 99%

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

Toga¹,

Nishino²,

Miyashita³

et al. 2018

Phys. Rev. B

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We examine the anisotropic properties of the exchange stiffness constant, A, for rare-earth permanent magnet, Nd2Fe14B, by connecting analyses with two different scales of length, i.e., Monte Carlo (MC) method with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a continuous magnetic model. The atomistic MC simulations are performed on the spin model of Nd2Fe14B constructed from ab-initio calculations, and the LLG micromagnetics simulations are performed with the parameters obtained by the MC simulations. We clarify that the amplitude and the thermal property of A depend on the orientation in the crystal, which are attributed to the layered structure of Nd atoms and weak exchange couplings between Nd and Fe atoms. We also confirm that the anisotropy of A significantly affects the threshold field for the magnetization reversal (coercivity) given by the depinning process.

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Temperature-dependent exchange stiffness and domain wall width in Co

Cited by 98 publications

References 45 publications

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Low-damping ferromagnetic resonance in electron-beam patterned, high-Q vanadium tetracyanoethylene magnon cavities

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

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