Laboratory for Functional Materials for Quantum Devices

Scientific results:

The project was aimed at developing, creating, and studying new nanophotonics materials that have significantly different magneto-optical and optomagnetic properties from those of homogeneous media. Thanks to specially designed nanostructures, the interaction between optical radiation passing through the material and the magnetic moments of the material is greatly enhanced. A key feature of this project is the combination of physical and technological research, which allowed us to produce nanophotonic materials with unique properties.

1. Monocrystalline iron garnet nanofilms were developed and synthesized for this project. These films have high specific polarization rotation due to the Faraday effect and exhibit magnetic properties such as saturation magnetization and magnetic anisotropy, which are required for solving the project's tasks.
2. All-dielectric magnetic metasurfaces for effective control of light with the help of magnetization. A new type of nanophotonics materials has been developed, created and studied - a completely dielectric magnetic metasurface based on a iron garnet nanofilm coated with silicon nanodisks. Due to the excitation of various optical modes of the metasurface (Mie modes, waveguide modes), the efficiency of the interaction of light with the magnetization of the material increases significantly in comparison with a homogeneous magnetic film. As a result, the magneto-optical effects are greatly enhanced. In addition, due to the Mie modes, a noticeable gyromagnetic response of the material arises at optical frequencies, which is extremely low for homogeneous films. The combination of gyromagnetic and gyroelectric responses makes such a metasurface bigyrotropic at optical frequencies. This leads to a new magneto-optical effect, which is not realized in a homogeneous film - modulation in a transverse magnetic field of the intensity of light passing through the metasurface and polarized perpendicular to the plane of incidence.
3. A new method for detecting short spin waves using dielectric metasurfaces and plasmonic nanogratings. The detection of short spin waves with light is limited by the Rayleigh diffraction limit. For optical registration of spin waves, whose wavelength is much smaller than the wavelength of light, it is proposed to use the developed dielectric metasurfaces (see Section 1), as well as plasmon nanogratings. Due to Mie-resonances of the metasurface, it was possible to obtain a spatially inhomogeneous sensitivity of light to various nanodomains. As a result, near the Mie resonance, light passing through the metasurface turns out to be insensitive to long spin waves and becomes highly sensitive to spin waves whose wavelength coincides with the period of the metasurface.
4. Spatially selective excitation of spin dynamics in a magnetic photonic crystal using femtosecond laser pulses. As a rule, spin waves are excited in a magnet simultaneously throughout its entire thickness, since the exciting microwave signal or laser beam is almost uniformly distributed over the thickness. For the first time, it was possible to optically excite spin waves with a selectivity over the thickness of the structure at the level of hundreds of nanometers. For this, a magnetic multilayer structure was developed and created - a magnetophotonic crystal, in which the spin angular momentum of a femtosecond pulse is distributed strongly inhomogeneously, which made it possible to excite spin waves in different layers of the structure with a very different efficiency. By tuning the wavelength of the pump laser, it was possible to change the ratio of the amplitudes of spin waves in different parts of the photonic crystal by a factor of 20.
5. A new method for detecting short spin waves using dielectric metasurfaces and plasmonic nanogratings. The detection of short spin waves with light is limited by the Rayleigh diffraction limit. For optical registration of spin waves, whose wavelength is much smaller than the wavelength of light, it is proposed to use the developed dielectric metasurfaces, as well as plasmon nanogratings. Due to Mie-resonances of the metasurface, it was possible to obtain a spatially inhomogeneous sensitivity of light to various nanodomains. As a result, near the Mie resonance, light passing through the metasurface turns out to be insensitive to long spin waves and becomes highly sensitive to spin waves whose wavelength coincides with the period of the metasurface.
6. The discovery of a novel magneto-optical effect: the topological Faraday effect. A novel effect due to the optical spin-orbit interaction, i.e. the interaction between the spin and orbital moments of a light beam, has been experimentally demonstrated. Such an interaction occurs when a light beam with a topological charge propagates through a transparent magnetic medium along its magnetization. As a result, the topological Faraday effect occurs: the rotation of the plane of polarization of light caused by the topological charge of the light beam. As a result, the total magneto-optical rotations of the light polarization plane for a plane wave and for an orbital light beam differ. The topological Faraday effect linearly depends on the orbital moment of the beam, but does not depend on its direction. The discovered effect is important for recording of static and dynamic magnetization distributions.
7. Optical excitation and identification of new properties of ultrafast spin dynamics in a non-collinear magnetic phase. Ferrimagnets containing several partially compensated magnetic sublattices are promising materials for ultrafast fully optical recording and information processing. Ferrimagnets can be in two magnetic phases, namely collinear and non-collinear ones. Spin dynamics excited in a ferrimagnet in a non-collinear phase using femtosecond laser pulses has been studied for the first time. At this several unusual properties of spin dynamics have been discovered. In particular, the non-collinearity of the ferrimagnet makes the exchange mode sensitive to an external magnetic field and brings its frequency closer to the frequency of the ferromagnetic mode. In addition, it was found that during the phase transition between the collinear and non-collinear phases, the ferromagnetic mode becomes soft, and its amplitude increases significantly, reaching 7°. This opens up new possibilities for ultrafast control of the precession of magnetization in ferrimagnets for non-thermal optical recording and information processing.
8. A new method for amplifying and controlling the directional pattern of spin waves when they are excited by femtosecond laser pulses. Excitation of spin waves at the required frequency and with the required directional pattern using short light pulses is one of the most important tasks of optomagnonics. A new method for controlling the directional pattern of spin waves in thin magnetic films is proposed, which is based on the excitation of waves using a periodic sequence of laser pulses with a repetition frequency of 1 GHz and 10 GHz. Such periodic exposure distinguishes a frequency near the repetition rate of laser pulses from a wide spectrum of spin waves. A spin-wave resonance occurs for spin waves at a given frequency, as a result of which the amplitude of spin waves increases by more than an order of magnitude, and their directional pattern narrows by several times. By changing the external magnetic field, one can control the wavelength of the spin waves, as well as change the radiation pattern. The proposed technique is extremely promising for the creation of magnonic devices of modern magnetic microelectronics.

Organizational and infrastructural changes:

The laboratory "Laboratory of Functional Materials for Quantum Devices" was created. The laboratory continues to function. Head of the laboratory Popov V.V., Scientific Director Belotelov V.I.

Education and personnel occupational retraining:

During the research, 4 dissertations for the degree of Doctor of Sciences were defended:

• Mikhailova Tatyana Vladislavovna "Structural and morphological features, optical and magneto-optical effects in nanophotonic elements and structures";
• Chernov Alexander Igorevich "Control of optical and magnetic properties of one-dimensional carbon nanomaterials";
• Yavorsky Maksim Aleksandrovich "Optical vortices in twisted and acousto-optic fiber gratings";
• Ignatyeva Darya Olegovna "Magnetophotonic nanostructures with optical resonances of surface and waveguide modes".

During the research, 6 dissertations for the Ph. D. degree were defended:

1. Semuk Evgeny Yuryevich "Ferromagnetic resonance in films of bismuth-substituted ferrites - garnets";
2. Vikulin Dmitry Vyacheslavovich "Optical vortices in circular optical fibers with bending regular and vortex acoustic modes";
3. Tomilina Olga Andreevna "Influence of direct and reverse percalation transition on the properties of metallic ultrathin films";
4. Sylgacheva Darya Anatolyevna "Multilayer magnetic nanostructures for thickness-selective control of waveguide modes and ultrafast optical excitation of spin dynamics";
5. Kozhaev Mikhail Aleksandrovich "Generation of spin waves by ultrashort laser pulses in dielectric magnetic materials";
6. Gusev Nikolay Aleksandrovich "Micro- and nanostructures based on epitaxial films of ferrite-garnet for magnetic sensors".

Two advanced training programs have been developed and implemented

1. "Optical recording of information on a ferrimagnet" - 10 people;
2. "Magnetophotonics and magnetoplasmonics" - 11 people.

Cooperation:

• Lomonosov Moscow State University,
• Russian Quantum Center,
• Institute for Physics of Microstructures RAS,
• Moscow Institute of Physics and Technology