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Register a new userMagnetic helicoidal dichroism in reflection by magnetic vortices
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Identifying and imaging spin textures of ever more complex magnetic structures has become a major challenge in the past decade, especially at ultrashort timescales. Most of current approaches are based on the analysis of their polarization and magnetization-dependent reflectivities. Based on our joint publication XXX XX XXXXXX, we introduce a different concept, centered on the coupling of magnetic structures with light beams carrying orbital angular momentum (OAM). Upon reflection by a magnetic vortex, an incoming beam with a unique value $ell$ of OAM gets enriched in the neighboring OAM modes $ellpm 1$. It results in anisotropic far-field images, which are identified as a Magnetic Helicoidal Dichroism (MHD) signal. Their analysis allow to retrieve the complex magneto-optical constants with excellent precision. This method, which does not require any polarization-resolved analysis, is promising for a quick identification of spin textures, including with attosecond to femtosecond time resolutions.
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We present the classical electromagnetic theory framework of reflection of a light beam carrying Orbital Angular Momentum (OAM) by an in-plane magnetic structure with generic symmetry. Depending on the magnetization symmetry, we find a change in the OAM content of the reflected beam due to magneto-optic interaction and an asymmetric far-field intensity profile. This leads to three types of Magnetic Helicoidal Dichroism (MHD), observed when switching the OAM of the incoming beam, the magnetization sign, or both. In cases of sufficient symmetries, we establish analytical formulas which link an experimentally accessible MHD signal up to $10%$ to the Magneto-Optical Kerr Effect (MOKE) constants. Magnetic vortices are particularly enlightening and promising targets, for which we explore the implications of our theory in the joint publication XX XXX XXXXXX.
We report on the experimental evidence of magnetic helicoidal dichroism, observed in the interaction of an extreme ultraviolet vortex beam carrying orbital angular momentum with a magnetic vortex. Numerical simulations based on classical electromagnetic theory show that this dichroism is based on the interference of light modes with different orbital angular momenta, which are populated after the interaction between the light phase chirality and the magnetic topology. This observation gives insight into the interplay between orbital angular momentum and magnetism, and sets the framework for the development of new analytical tools to investigate ultrafast magnetization dynamics.
Surface magnetic properties of perovskite manganites have been a recurrent topic during last years since they play a major role in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sensitivity to magnetic and chemical variations across the sample depth. Nevertheless, the application of the sum rules for the determination of the spin magnetic moment might lead to uncertainties as large as 40% in case of Mn ions. To overcome this problem we present an alternative approach consisting of using X-ray magnetic circular dichroism in reflection geometry. Fit of the data by using a computer code based in a 4X4 matrix formalism leads to realistic results. In particular, we show that surface and interface roughness are of major relevance for a proper description of the experimental data and a correct interpretation of the results. By using such an approach we demonstrate the presence of a narrow surface region with strongly depressed magnetic properties in La2/3Ca1/3MnO3 thin films.
Superfluid vortices are quantum excitations carrying quantized amount of orbital angular momentum in a phase where global symmetry is spontaneously broken. We address a question of whether magnetic vortices in superconductors with dynamical gauge fields can carry nonzero orbital angular momentum or not. We discuss the angular momentum conservation in several distinct classes of examples from crossdisciplinary fields of physics across condensed matter, dense nuclear systems, and cosmology. The angular momentum carried by gauge field configurations around the magnetic vortex plays a crucial role in satisfying the principle of the conservation law. Based on various ways how the angular momentum conservation is realized, we provide a general scheme of classifying magnetic vortices in different phases of matter.
The optical properties of some nanomaterials can be controlled by an external magnetic field, providing active functionalities for a wide range of applications, from single-molecule sensing to nanoscale nonreciprocal optical isolation. Materials with broadband tunable magneto-optical response are therefore highly desired for various components in next-generation integrated photonic nanodevices. Concurrently, hyperbolic metamaterials received a lot of attention in the past decade since they exhibit unusual properties that are rarely observed in nature and provide an ideal platform to control the optical response at the nanoscale via careful design of the effective permittivity tensor, surpassing the possibilities of conventional systems. Here, we experimentally study magnetic circular dichroism in a metasurface made of type-II hyperbolic nanoparticles on a transparent substrate. Numerical simulations confirm the experimental findings, and an analytical model is established to explain the physical origin of the observed magneto-optical effects, which can be described in terms of the coupling of fundamental electric and magnetic dipole modes with an external magnetic field. Our system paves the way for the development of nanophotonic active devices combining the benefits of sub-wavelength light manipulation in hyperbolic metamaterials supporting a large density of optical states with the ability to freely tune the magneto-optical response via control over the anisotropic permittivity of the system.
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