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Magneto-optical cerium-substituted yttrium iron garnet (Ce:YIG) thin films display Faraday and Kerr rotation (rotation of light polarisation upon transmission and reflection, respectively) as well as a nonreciprocal phase shift due to their non-zero off-diagonal permittivity tensor elements, and also possess low optical absorption in the near-infrared. These properties make Ce:YIG useful in providing nonreciprocal light propagation in integrated photonic circuits, which is essential for accomplishing energy-efficient photonic computation and data transport architectures. In this study, 80 nm-thick Ce:YIG films were grown on Gadolinium Gallium Garnet substrates with (100), (110) and (111) orientations using pulsed laser deposition. The films had bulk-like structural and magnetic quality. Faraday and Kerr spectroscopies along with spectroscopic ellipsometry were used to deduce the complete permittivity tensor of the films in the ultraviolet, visible and near-infrared spectral region, and the magneto-optical figure of merit as a function of wavelength was determined. The samples showed the highest IR Faraday rotation reported for thin films of Ce:YIG, which indicates the importance of this material in development of nonreciprocal photonic devices.

Phases of matter are ubiquitous with everyday examples including solids and liquids. In reduced dimensions, particular phases, such as the 2D hexatic phase and corresponding phase transitions occur. A particularly exciting example of 2D ordered systems are skyrmion lattices, where in contrast to previously studied 2D colloid systems, the skyrmion size and density can be tuned by temperature and magnetic fields. This allows for the system to be driven from a liquid phase to the onset of a hexatic phase as deduced from the analysis of the hexagonal order. Using coarse-grained molecular dynamics simulations of soft disks, the skyrmion interaction potentials are determined, and it is found that the simulations are able to reproduce the phase behavior. This shows that not only the static behavior of skyrmions is qualitatively well described in terms of a simple 2D model system but skyrmion lattices are versatile and tunable 2D model systems that allow for studying phases and phase transitions in reduced dimensions.

In this work, we present a systematic study of optical and magneto-optical properties of Y 3-x Bi x Fe 5 O 12 thin films with various Bi concentrations (x = 1.5, 2, 2.5, 3) prepared by Metal Organic Decomposition on Gd 3 Ga 5 O 12 (100) substrates. We used magneto-optical spectroscopy and spectroscopic ellipsometry. Spectral dependence of complex refraction indexes obtained from ellipsometric measurements revealed increasing optical absorption with increasing Bi concentrations. Faraday and Kerr magneto-optical spectra measured in the photon energy range from 1.5 to 5.5 eV clearly demonstrated that the increasing Bi concentration enhances the spin-orbit coupling and influences the magnetooptical effect. Using the magneto-optical and ellipsometric experimental data we deduced a spectral dependence of complete permittivity tensor in a wide spectral range. Comparison of obtained results with the results reported on Liquid Phase Epitaxy bulk-like garnets with small Bi concentrations showed agreement and confirmed a high optical and magneto-optical quality of investigated films.

lator devices is commonly a MO iron garnet material, in particular yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) with substituents such as Ce or Bi to increase the MO performance. [5][6][7][8][9][10][11][12][13][14][15] However, the integration of garnets on a Si (or other semiconductor) platform is challenging due to the incompatible lattice parameters and the thermal expansion mismatch between garnets and common semiconductor substrates. [6][7][8][9][10][11][12][13][14][15][16] Moreover, crystallization of the garnet phase usually requires a high thermal budget. Garnets formed on semiconductor substrates are polycrystalline and exhibit higher optical absorption than single crystal films. Furthermore, impurity phases such as YFeO 3 , Fe 2 O 3 , and Bi 2 O 3 can form during the crystallization process, [17] which contributes to optical loss. These factors result in inferior optical performance of polycrystalline MO garnet films compared to the bulk garnet material, and a lower figure of merit (FoM), defined as the ratio of the Faraday rotation to the absorption coefficient per length of the material.Considerable work has been done on growth of garnet films on semiconductors to enable demonstrations of isolators and modulators. [6][7][8][9][10][11][12][13][14][15][16] The first monolithically integrated optical isolator [6] used 80 nm thick Ce:YIG which was grown by pulsed laser deposition (PLD) on a pre-annealed 20 nm thick YIG seed layer to induce crystallization of the Ce:YIG. A simplified PLD process was introduced by Sun et al. [11] where the YIG seed layer was placed on top of the MO garnet and both layers were crystallized simultaneously by rapid thermal annealing (RTA). This top-seedlayer process places the MO garnet in direct contact with the underlying Si waveguide, maximizing the coupling of light from the waveguide to the MO cladding, but it has only been applied to Ce:YIG. Recently rare-earth garnets have been developed that crystallize on Si and quartz without a seed layer, including sputter-deposited terbium iron garnet (TIG) and Bi-doped TIG (Bi:TIG). [18,19] Growth of MO materials on the sidewall of the waveguide can enable a wider range of device designs, including isolators for transverse electric (TE) polarization. Integrated semiconductor lasers emit TE-polarized light, and TE mode isolation using NRPS requires placement of the MO material on the sidewall of the waveguide to break left-right symmetry. [18,20,21] However, the NRPS-based integrated optical isolators that have been experimentally demonstrated are made with the MO material on the top or bottom surface of the waveguide, which isolates only the transverse magnetic (TM) polarization. [6][7][8][11][12][13][14] It is therefore essential to establish deposition conditions that yield Thin film magneto-optical (MO) materials are enablers for integrated nonreciprocal photonic devices such as isolators and circulators. Films of polycrystalline bismuth-substituted yttrium iron garnet (Bi:YIG) have been grown on silicon substrates and waveguide d...

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The hybridization of magnons (spin waves) with phonons, if sufficiently strong and comprising of long wavelength excitations, may offer a new playground when manipulating the magnetically ordered systems with light. Applying a magnetic field to a quasi-two-dimensional antiferromagnet, FePS 3 , we tune the magnon-gap excitation to coincide with the initially lower-in-energy phonon modes. Hybrid magnon-phonon modes, the magnon polarons are unveiled with the demonstration of a pronounced avoided crossing between the otherwise bare magnon and phonon excitations. The magnon polarons in FePS 3 are traced with Raman scattering experiments. However, as we show, they also couple directly to terahertz photons, evoking their further explorations in the domain of antiferromagnetic optospintronics. The magnon-phonon coupling is also discussed as a possible reason of the magnon mode splitting observed in the absence of a magnetic field.

The Faraday effect is a representative magneto-optical phenomenon, resulting from the transfer of angular momentum between interacting light and matter in which time-reversal symmetry has been broken by an externally applied magnetic field. Here we report on the Faraday rotation induced in the prominent 3D topological insulator Bi2Se3 due to bulk interband excitations. The origin of this non-resonant effect, extraordinarily strong among other non-magnetic materials, is traced back to the specific Dirac-type Hamiltonian for Bi2Se3, which implies that electrons and holes in this material closely resemble relativistic particles with a non-zero rest mass.