Adekunle Olusola Adeyeye

Antiartificial spin ice (AASI), realized through spin-ice-derived antidot lattices of stadium-shaped holes in continuous Permalloy ( Ni 81 Fe 19 ) films, provides a powerful route for embedding geometry-induced magnetic anisotropy within a connected magnonic medium. Here, homogeneous and bicomponent AASI lattices are investigated through a combined experimental and micromagnetic approach, establishing a direct link between lattice geometry, magnetization reversal, and spin-wave (SW) dynamics. Magneto-optical Kerr effect measurements, Brillouin light scattering spectroscopy, and simulations reveal that antidot size, lattice heterogeneity, and magnetic field orientation collectively govern both equilibrium states and dynamic excitations. The static response exhibits pronounced angular anisotropy in coercivity and remanence, with bicomponent lattices showing distinct reversal pathways and shifted anisotropy extrema relative to homogeneous systems. These variations are directly reflected in the SW spectra, where edge-, node-, and domain-wall-localized modes, as well as mode splitting and frequency flattening, emerge as signatures of geometry-induced magnetization textures. The excellent agreement between experiment and simulation establishes a microscopic connection between equilibrium magnetic configurations and SW excitations. These findings demonstrate a direct transfer of configurational anisotropy into tunable magnonic functionality, highlighting AASI as a versatile platform for geometry-encoded SW architectures.

Magnetization dynamics in laterally confined nanostructures have gained significant attention in recent years due to their promising use in magnetic logic, sensing technologies, and microwave applications. Achieving reliable integration of these systems into on-chip devices requires a thorough understanding of both their magnetization reversal processes and microwave responses. Nanodots, nanowires, and artificial spin-ice (ASI) lattices each exhibit distinct advantages and rich ferromagnetic resonance behavior shaped by their geometries and intrinsic magnetic interactions. In this review, we summarize the static and dynamic properties of a variety of single-layer and trilayer nanostructures—including nanodots, nanowires, width-modulated nanowires, and ASI systems—drawing primarily on our previous investigations. The insights gained from these studies offer valuable guidance for the development of reconfigurable magnonic crystals intended for next-generation microwave components and wave-based spintronic technologies.

The interfacial Dzyaloshinskii–Moriya interaction (iDMI) plays a vital role in stabilizing chiral magnetic textures and enabling nonreciprocal spin-wave propagation, both of which are essential for the development of next-generation spintronic devices. Controlling iDMI through material design and interface engineering is therefore important for achieving more energy-efficient information technologies. CoFeB/Pt heterostructures are particularly versatile due to their adjustable magnetic and spin–orbit properties. In this study, we examine how stacking sequence, interface quality, and magnetic moment density influence iDMI in CoFeB/Pt thin films using magnetometry and Brillouin light scattering. We find that changing the layer order, creating symmetric stacks, or inserting spacer layers significantly alters spin-wave nonreciprocity. Notably, the frequency shift when CoFeB is deposited on top of Pt is more than twice, and the iDMI constant is almost four times higher than that when Pt is on top of the CoFeB; the effects related to ferromagnet thickness and moment density confirm that the origin is at the interface. These findings offer practical insights into interface engineering for tunable chiral spin dynamics in ultrathin magnetic films.

Custom-engineered nanomagnonic waveguides with enhanced nonlinear properties are pivotal for advancing next-generation wave-based spintronic technologies. In this work, we systematically explore how lattice geometry influences the linear and nonlinear dynamics of Permalloy antidot waveguides. Three lattice configurations—square, rhomboid, and honeycomb—are examined. Our results reveal that introducing antidots generates localized magnon modes alongside propagating spin waves, with geometry strongly dictating localization behavior. Spin waves exhibit selective channel propagation, and in the nonlinear regime, we observe the presence of both integer and fractional harmonics. The 1.5fexc mode displays behavior similar to that of the fundamental modes, propagating through the channels, while the second harmonic reveals antisymmetric characteristics with multiple nodes across the channels. Notably, harmonic-generation efficiency in honeycomb lattices is nearly four times higher than in reference waveguides without antidots, and the second harmonic's performance depends on lattice positioning. Direct spin-wave imaging via Brillouin light microscopy confirms these findings, highlighting the promise of geometry-tailored antidot waveguides for magnon-based computing applications.

We have systematically investigated, using magneto-optical Kerr effect, the angular dependence of magnetization reversal in circular and rounded rectangular Ni₈₁Fe₁₉ nanorings under both isolated and strongly interacting conditions.

The coupling of lattice and magnetization dynamics is a topic of growing interest, with significant implications for novel solid-state technologies. In this work, we investigate arrays of ferromagnetic Fe/Permalloy nanostripes. A time-resolved optical approach enables the study of magnonic and phononic excitations, as well as their coupling at mode crossings. The field-dependent frequencies were also measured using Brillouin light scattering spectroscopy and corroborated by micromagnetic simulations for different in-plane directions of an external magnetic field. We find that the acoustic and magnonic excitations can be tuned in frequency and magnetic field by adjusting the array periodicity, filling ratio, as well as the orientation of the nanostripes relative to the external field. Additionally, we discuss the presence of features in the signal intensity at the magnon–phonon crossings, introduced by dynamical phase effects due to the impulsive coherent excitation.

The magnetization dynamics of square arrays of circular antidots fabricated on Si(001) substrates using deep ultraviolet lithography with a 248 nm exposing wavelength have been studied. The effects of thickness (40 nm and 80 nm) and the in-plane direction of the applied magnetic field on the magnetostatic mode energies were investigated through ferromagnetic resonance experiments and micromagnetic simulations for both thicknesses. The experimental results and the simulations allowed the determination of nature of the magnetostatic modes nature measured at angles of 0° and 45° between the applied magnetic field and the axis of the square array. Notably, in this geometry, the main modes do not disapear when the sample is rotated; instead, the localization of the modes follow the rotation of the applied field, with a variation in measured intensity directly related to the surface area occupied by the localized mode.