arXiv subjects

Waleed I. Waseer

Publications and source records attributed to Waleed I. Waseer.

3 recordsLinked to original sources

arXiv2026

Nonlinear Dynamics of Hopfion for Frequency Multiplication

Hopfions, associated with higher-dimensional topology through the Hopf fibration, exhibit {exotic} features like {complex knot} and improved stability compared to skyrmions, enhancing their appeal for innovative applications. In this paper, we study the nonlinear response of magnetic Hopfion to microwave fields. {We observe the emergence of higher-order harmonics of the driving microwave field as it interacts with the Hopfion}. By carefully selecting the {driving frequency, the corresponding harmonic can efficiently excite localized magnon state of a Hopfion. Our results demonstrate the promising potential of hopfions in nonlinear magnonics.

cond-mat.mes-hall↗

arXiv2026

Engineering nonlinear magnon scattering in artificial spin ice via vertex dipolar control

Artificial spin ice (ASI), composed of geometrically frustrated arrays of interacting nanoislands, provides a versatile platform for reprogrammable magnonic functionality. However, the commonly used geometric control parameters such as island length, width, and aspect ratio simultaneously modify the island footprint, inter island dipolar spacing, and shape anisotropy, making it difficult to tune the nonlinear response independently of the linear spectrum and lattice density. Using micromagnetic simulations of kagome ASI under strong microwave drive, we identify edge curvature as a geometric degree of freedom that separates nonlinear magnon scattering from the island footprint. Sharp tipped islands predominantly generate integer harmonics, whereas dumbbell shaped tips produce a transition toward subharmonic rich spectra by concentrating demagnetizing and exchange fields near the island ends without changing the overall island volume or lattice spacing. By mapping the curvature and drive parameter space, we identify a continuous threshold for subharmonic onset controlled by tip curvature. We further show that the angular dependence of the second harmonic amplitude reverses between sharp and dumbbell geometries, providing an experimentally accessible signature of curvature localized nonlinearity. Width and leg length asymmetry can also modify harmonic amplitudes, but they do not remove the intrinsic trade off between footprint and coupling. These results establish tip curvature as a footprint preserving design parameter for engineering nonlinear magnon scattering in ASI, with implications for reconfigurable magnonic devices.

cond-mat.mes-hall↗

arXiv2022

Thermal hysteresis in scattering by vanadium-dioxide spheres

Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal on being heated from 58 deg C to 72 deg C, the transformation being reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is less than 1100 nm, but from a dissipative dielectric to a plasmonic metal (or vice versa) if the free-space wavelength exceeds 1100 nm. Calculating the extinction, total scattering, absorption, radiation-pressure, back-scattering, and forward-scattering efficiencies of a VO2 sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, back-scattering, and absorption efficiencies for free-space wavelength less than 1100 nm, and (ii) the forward-scattering, back-scattering, total scattering, and absorption efficiencies for free-space wavelength more than 1100 nm. Vacuum and null-permittivity quasistates occur between 58 deg C and 72 deg C, when tetragonal VO2 is a plasmonic metal, once each on the heating branch and once each on the cooling branch of thermal hysteresis. But none of the six efficiencies show significant differences between the two quasistates.

physics.optics↗