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Ashokan, Vinod; Khater, A.; Ghantous, Michel Abou; Ghader, Doried

doi:10.1016/j.jmmm.2015.02.004

Cited by 10 publications

(6 citation statements)

References 35 publications

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“…The solutions ± are adopted for ψ ± respectively, which yields the functional forms φ ± i = u i1 e − ± 1 x e ipy + u i2 e − ± 2 x e ipy . The four-band formalism hence generates 16 coefficients u ij ; i = 1, ..4, j = 1, 2 , to be determined via boundary conditions derived using the matching method 26,27,[55][56][57][58][59] .…”

Section: Methodsmentioning

confidence: 99%

Valley-polarized domain wall magnons in 2D ferromagnetic bilayers

Ghader

2020

Sci Rep

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Valleytronics is a pioneering technological field relying on the valley degree of freedom to achieve novel electronic functionalities. Topological valley-polarized electrons confined to domain walls in bilayer graphene were extensively studied in view of their potentials in valleytronics. Here, we study the magnonic version of domain wall excitations in 2D honeycomb ferromagnetic bilayers (FBL) with collinear order. In particular, we explore the implications of Dzyaloshinskii-Moriya interaction (DMI) and electrostatic doping (ED) on the existence and characteristics of 1D magnons confined to layer stacking domain walls in FBL. The coexistence of DMI and ED is found to enrich the topology in FBL, yet the corresponding domain wall magnons do not carry a well-defined valley index. On the other hand, we show that layer stacking domain walls in DMI-free FBL constitute 1D channels for ballistic transport of topological valley-polarized magnons. Our theoretical results raise hope towards magnon valleytronic devices based on atomically thin topological magnetic materials.

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Section: Methodsmentioning

confidence: 99%

Valley-polarized domain wall magnons in 2D ferromagnetic bilayers

Ghader

2020

Sci Rep

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“…The DMI term in H T can be rewritten in terms of a scalar product 22 which unifies the treatment of the exchange and the DMI parts of H T (Supplementary Notes 1 and 3). The effective exchange fields H α l acting on the sublattice magnetizations M α l can then be derived from the Heisenberg Hamiltonian as [19][20][21][22][41][42][43][44][45][46]…”

Section: Resultsmentioning

confidence: 99%

Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers

Ghader

2020

Sci Rep

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Twistronics is currently one of the most active research fields in condensed matter physics, following the discovery of correlated insulating and superconducting phases in twisted bilayer graphene (tBLG). Here, we present a magnonic analogue of tBLG. We study magnons in twisted ferromagnetic bilayers (tFBL) with collinear magnetic order, including exchange and weak Dzyaloshinskii-Moriya interactions (DMI). For negligible DMI, tFBL presents discrete magnon magic angles and flat moiré minibands analogous to tBLG. The DMI, however, changes the picture and renders the system much more exotic. The DMI in tFBL induces a rich topological magnon band structure for any twist angle. The twist angle turns to a control knob for the magnon valley Hall and Nernst conductivities. Gapped flat bands appear in a continuum of magic angles in tFBL with DMI. In the lower limit of the continuum, the band structure reconstructs to form several topological flat bands. The luxury of twist-angle control over band gaps, topological properties, number of flat bands, and valley Hall and Nernst conductivities renders tFBL a novel device from fundamental and applied perspectives.

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“…We emphasize that the basic physical variables, such as the exchange and sublattice magnetizations for Co and Gd sites for the embedded layered nanostructures between cobalt leads, are necessary elements for the computations of the spin dynamics of magnetic nanojunctions in the field of magnonics, as for the ballistic magnon transport [24]. In Table 1 we present an example for the calculated spin variables < S Co > ≈ 1 throughout the system, and < S Gd > on the identified atomic planes 1, 2, .., ℓ, of the layered ...Co][2 ′ 22 ′ ][Co... and ...Co][3 ′ 33 ′ ][Co... nanostructures between cobalt leads, at room temperature T=300K and stable eutectic compositions c ≤ 0.5, using the EFT-MFT combined method.…”

Section: Gdmentioning

confidence: 99%

“…These triple-nanostructure systems are more complex than the previously studied single-nanostructure systems [23]. The present work is hence motivated by the objective to compute the salient magnetic properties of the triple-nanostructures for fundamental interest, and the scattering and ballistic transport of spin waves incident from cobalt leads on complex ferrimagnetic cobalt-gadolinium nanojunction systems [24]. Such complex systems have as it turns out a richer and wider range of spin wave filtering properties.…”

Section: Introductionmentioning

confidence: 99%

Computational modeling of sublattice magnetizations of nano-magnetic layered materials

Ashokan¹,

Khater²,

Ghantous³

2020

Preprint

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In the present work, we model the salient magnetic properties of the alloy layered ferrimagnetic nanostructuresbetween magnetically ordered cobalt leads. The effective field theory (EFT) Ising spin method is used to compute reliable J Co−Co and J Gd−Gd exchange values for the pure cobalt and gadolinium materials in comparison with experimental data. Using the combined EFT and mean field theory (MFT) spin methods, the sublattice magnetizations of the Co and Gd sites on the individual hcp basal planes of the layered nanostructures, are calculated and analyzed. The sublattice magnetizations, effective magnetic moments per site, and compensation characteristics on the individual hcp atomic planes of the embedded nanostructures are presented as a function of temperature and the thicknesses of the layered ferrimagnetic nanostructures, for different stable eutectic concentrations c ≤ 0.5. In the absence of first principles calculations for these basic physical variables for the layered nanostructures between cobalt leads, the combined EFT and MFT approach, and appropriate magnetic modeling of the well-defined interfaces of these systems, yield the only available information for them at present. These magnetic variables are necessary for spin dynamic computations, and for the ballistic magnon transport across embedded nanojunctions in magnonics. The model is general, and may applied directly to other composite magnetic elements and embedded nanostructures.

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Spin wave ballistic transport properties of [Co1−cGdc

Cited by 10 publications

References 35 publications

Valley-polarized domain wall magnons in 2D ferromagnetic bilayers

Valley-polarized domain wall magnons in 2D ferromagnetic bilayers

Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers

Computational modeling of sublattice magnetizations of nano-magnetic layered materials

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