Extreme anti-reflection enhanced magneto-optic Kerr effect microscopy

Strong Magneto-Optical Kerr Effects in Ni-Doped ZnO Nanolaminate Structures Obtained by Atomic Layer Deposition

The magneto-optical (MO) Kerr effects for ZnO and ZnO:Ni-doped nanolaminate structures prepared using atomic layer deposition (ALD) have been investigated. The chemical composition and corresponding structural and morphological properties were studied using XRD and XPS and compared for both nanostructures. The 2D array gradient maps of microscale variations of the Kerr angle polarization rotation were acquired by means of MO Kerr microscopy. The obtained data revealed complex behavior and broad statistical dispersion and showed distinct qualitative and quantitative differences between the undoped ZnO and ZnO:Ni-doped nanolaminates. The detected magneto-optical response is extensively inhomogeneous in ZnO:Ni films, and a giant Kerr polarization rotation angle reaching up to ~2° was established. This marks the prospects for further development of magneto-optical effects in ALD ZnO modified by transition metal oxide nanostructures.

Magneto-Optical and Muliferroic Properties of Transition-Metal (Fe, Co, or Ni)-Doped ZnO Layers Deposited by ALD

ZnO doped with transition metals (Co, Fe, or Ni) that have non-compensated electron spins attracts particular interest as it can induce various magnetic phenomena and behaviors. The advanced atomic layer deposition (ALD) technique makes it possible to obtain very thin layers of doped ZnO with controllable thicknesses and compositions that are compatible with the main microelectronic technologies, which further boosts the interest. The present study provides an extended analysis of the magneto-optical MO Kerr effect and the dielectric properties of (Co, Fe, or Ni)-doped ZnO films prepared by ALD. The structural, magneto-optical, and dielectric properties were considered in relation to the technological details of the ALD process and the corresponding dopant effects. All doped samples show a strong MO Kerr behavior with a substantial magnetization response and very high values of the Kerr polarization angle, especially in the case of ZnO/Fe. In addition, the results give evidence that Fe-doped ZnO also demonstrates a ferroelectric behavior. In this context, the observed rich and versatile physical nature and functionality open up new prospects for the application of these nanostructured materials in advanced electronic, spintronic, and optical devices.

Spontaneous generation and active manipulation of real-space optical vortices

Optical vortices are beams of light that carry orbital angular momentum¹, which represents an extra degree of freedom that can be generated and manipulated for photonic applications^2-8. Unlike vortices in other physical entities, the generation of optical vortices requires structural singularities^9-12, but this affects their quasiparticle nature and hampers the possibility of altering their dynamics or making them interacting^13-17. Here we report a platform that allows the spontaneous generation and active manipulation of an optical vortex-antivortex pair using an external field. An aluminium/silicon dioxide/nickel/silicon dioxide multilayer structure realizes a gradient-thickness optical cavity, where the magneto-optic effects of the nickel layer affect the transition between a trivial and a non-trivial topological phase. Rather than a structural singularity, the vortex-antivortex pairs present in the light reflected by our device are generated through mathematical singularities in the generalized parameter space of the top and bottom silicon dioxide layers, which can be mapped onto real space and exhibit polarization-dependent and topology-dependent dynamics driven by external magnetic fields. We expect that the field-induced engineering of optical vortices that we report will facilitate the study of topological photonic interactions and inspire further efforts to bestow quasiparticle-like properties to various topological photonic textures such as toroidal vortices, polarization and vortex knots, and optical skyrmions.

Tunable Polarized Microcavity Characterized by Magnetic Circular Dichroism Spectrum

Tunable resonator is a powerful building block in fields like color filtering and optical sensing. The control of its polarization characteristics can significantly expand the applications. Nevertheless, the methods for resonator dynamic tuning are limited. Here, a magnetically regulated circular polarized resonant microcavity is demonstrated with an ultrathin ferrimagnetic composite metal layer Ta/CoTb. We successfully tuned the cavity resonant frequency and polarization performance. A huge magnetic circular dichroism (MCD) signal (∼3.41%) is observed, and the microcavity valley position shifts 5.41 nm when a small magnetic field is applied. This resonant cavity has two-stable states at 0 T due to the magnetic remanence of CoTb film and can be switched using a tiny magnetic field (∼0.01 T). Our result shows that the ferrimagnetic film-based tunable microcavity can be a highly promising candidate for on-chip magneto-optical (MO) devices.

Experimental Probing of Canonical Electromagnetic Spin Angular Momentum Distribution via Valley-Polarized Photoluminescence

The canonical formulation of the spin angular momentum (SAM) of light has been suggested recently as an extension of the Abraham-Minkowski controversy. However, experimental substantiations of the canonical SAM for localized fields have not been reported yet. We directly probe the locally distributed canonical SAM tailored by a plasmonic nanostructure via the valley-polarized photoluminescence of the multilayer WS_{2}. The spectrum-resolved measurement details the spin-selective Raman scattering and exciton emission beyond the conventional manner of employing circularly polarized paraxial waves.

Band structure analysis of the magneto-optical effect in bcc Fe

Magneto-optical effects are among the basic tools for characterization of magnetic materials. Although these effects are routinely calculated by the ab initio codes, there is very little knowledge about their origin in the electronic structure. Here, we analyze the magneto-optical effect in bcc Fe and show that it originates in avoided band-crossings due to the spin-orbit interaction. Therefore, only limited number of bands and k-points in the Brillouin zone contribute to the effect. Furthermore, these contributions always come in pairs with opposite sign but they do not cancel out due to different band curvatures providing different number of contributing reciprocal points. The magneto-optical transitions are classified by the dimensionality of the manifold that is formed by the hybridization of the generating bands as one- or two-dimensional, and by the position relative to the magnetization direction as parallel and perpendicular. The strongest magneto-optical signal is provided by two-dimensional parallel transitions.

Nonlinear Circular Dichroism in Mie-Resonant Nanoparticle Dimers

We studied the nonlinear response of a dimer composed of two identical Mie-resonant dielectric nanoparticles illuminated normally by a circularly polarized light. We developed a general theory describing hybridization of multipolar modes of the coupled nanoparticles and reveal nonvanishing nonlinear circular dichroism (CD) in the second-harmonic generation (SHG) signal enhanced by the multipolar resonances in the dimer, provided its axis is oriented under an angle to the crystalline lattice of the dielectric material. We supported our multipolar hybridization theory by experimental results obtained for the AlGaAs dimers placed on an engineered substrate.