The infrared optical, magneto-optical and magnetostrictive properties of CoFe2O4 single crystal are considered. The magneto-transmission and magneto-reflection of natural light in magnetostrictive CoFe2O4 spinel are studied in the Voight experimental geometry. These magneto-optical effects are very high and associate with a change of the fundamental absorption edge and impurity absorption bands under magnetic field. It is presented the effects strongly depend on both the magnitude and orientation of magnetic field relative to the crystallographic axes of the crystal. The clear connection between magneto-absorption of light in the infrared spectral range and magnetostriction of CoFe2O4 spinel is established. The contribution of magnetostriction to the magnetic anisotropy constant of the CoFe2O4 crystal is shown to be abnormally great.
We have studied the magneto-optical Kerr effect and optical reflectance of perpendicular magnetized Co/Pt films on self-assembly two-dimensional polystyrene spheres. It is shown that the magneto-optical and the reflectance spectra are correlated to each other. Calculations have shown that the magneto-optical Kerr rotation and the Kerr ellipticity spectra are governed by the resonant coupling of light to the excitations of surface plasmon polaritons and modified by the sphere diameters. These effects lead to the possibility of developing new magnetoplasmonic nanosensors.
We report on observation of a magneto-optical effect quadratic in magnetization (Cotton-Mouton effect) in 50 nm thick layer of Yttrium-Iron Garnet (YIG). By a combined theoretical and experimental approach, we managed to quantify both linear and quadratic magneto-optical effects. We show that the quadratic magneto-optical signal in the thin YIG film can exceed the linear magneto-optical response, reaching values of 450 urad that are comparable with Heusler alloys or ferromagnetic semiconductors. Furthermore, we demonstrate that a proper choice of experimental conditions, particularly with resp…
We experimentally demonstrate that in magnetostrictive ferrimagnetic single crystal of CoFe2O4 there is clear correlation between magnetostriction and magnetoreflection of unpolarized light in the infrared range. The influence of magnetic field on specular reflection is likely to be indirect: application of a magnetic field results in strong strain and deformation of the crystal lattice, which leads to the change in electron energy structure and hence reflection spectrum.
We have studied the magneto-optical and magnetotrasnport properties of GaMnAs thin films with high Mn concentrations (x= 12.2 - 21.3%) grown by molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by decreasing the growth temperature to as low as 150-190 degree C and by reducing the film thickness to 10 nm in order to prevent precipitation of hexagonal MnAs clusters. Magnetic circular dichroism (MCD) and anomalous Hall effect measurements indicate that these GaMnAs films have the nature of intrinsic ferromagnetic semiconductors with high ferromagnetic transition temperature …
Chromium trihalides (CrI$_3$, CrBr$_3$ and CrCl$_3$) form a prominent family of isostructural insulating layered materials in which ferromagnetic order has been observed down to the monolayer. Here we provide a comprehensive computational study of magneto-optical properties that are used as probes for the monolayer ferromagnetic order: magnetic circular dichroism and magneto-optic Kerr effect. Using a combination of density functional and Bethe-Salpeter theories, we calculate both the optical absorption and the magneto-optical Kerr angle spectra, including both excitonic effects and spinorial …
Using symmetry arguments and a tight-binding model, we show that for layered collinear anti- ferromagnets, magneto-optic effects can be generated and manipulated by controlling crystal symmetries through a gate voltage. This provides a promising route for electric field manipulation of the magneto-optic effects without modifying the underlying magnetic structure. We further demonstrate the gate control of magneto-optic Kerr effect (MOKE) in bilayer MnPSe3 using first-principles calculations. The field-induced inversion symmetry breaking effect leads to gate-controllable MOKE whose direction of…
The influence of surface plasmons on the magneto-optic activity in a two-dimensional hexagonal array is addressed. The experiments were performed using hexagonal array of circular holes in a ferromagnetic Ni film. Well pronounced troughs are observed in the optical reflectivity, resulting from the presence of surface plasmons. The surface plasmons are found to strongly enhance the magneto-optic response (Kerr rotation), as compared to a continuous film of the same composition. The influence of the hexagonal symmetry of the pattern on the coupling between the plasmonic excitations is demonstrat…
We report a joint theoretical and experimental study focused on understanding the optical and magneto-optical properties of Co-based full-Heusler compounds. We show that magneto-optical spectra calculated within ab-initio density functional theory are able to uniquely identify the features of the experimental spectra in terms of spin resolved electronic transitions. As expected for 3d-based magnets, we find that the largest Kerr rotation for these alloys is of the order of 0.3o in polar geometry. In addition, we demonstrate that (i) multilayered structures have to be carefully handled in the t…
Reflecting the fundamental interactions of polarized light with magnetic matter, magneto-optical effects are well known since more than a century. The emergence of these phenomena is commonly attributed to the interplay between exchange splitting and spin-orbit coupling in the electronic structure of magnets. Using theoretical arguments, we demonstrate that topological magneto-optical effects can arise in noncoplanar antiferromagnets due to the finite scalar spin chirality, without any reference to exchange splitting or spin-orbit coupling. We propose spectral integrals of certain magneto-opti…
Optical absorption and transverse Kerr effect spectra, resistivity and magnetoresistance of La$_{1-x}$Sr$_{x}$CoO$_3$ ($x=0.15, 0.25, 0.35$) films have been studied. The temperature dependencies of the optical and magneto-optical properties of the films exhibit features, which can be attributed to the transition of the Co$^{3+}$ ions from the low-spin state (S=0) to the intermediate-spin state (S=1) and to orbital ordering of the Co$^{3+}$ ions in the latter state. The evolution of the properties influenced by doping with Sr is interpreted on the basis of the phase separation model.
Magneto-optical response, i.e. optical response in the presence of a magnetic field, is commonly used for characterization of materials and in optical communications. However, quantum mechanical description of electric and magnetic fields in crystals is not straightforward as the position operator is ill defined. We present a reformulation of the density matrix perturbation theory for time-dependent electromagnetic fields under periodic boundary conditions, which allows us to treat the orbital magneto-optical response of solids at the \textit{ab initio} level. The efficiency of the computation…
The recent discovery of magnetism in atomically thin layers of van der Waals crystals has created great opportunities for exploring light-matter interactions and magneto-optical phenomena in the two-dimensional limit. Optical and magneto-optical experiments have provided insights into these topics, revealing strong magnetic circular dichroism and giant Kerr signals in atomically thin ferromagnetic insulators. However, the nature of the giant magneto-optical responses and their microscopic mechanism remain unclear. Here, by performing first-principles GW and Bethe-Salpeter equation calculations…
Magneto-optical absorption by the quantum dot (QD) with impurity center (IC or D(-)-center) complexes synthesized in a transparent dielectric matrix, with consideration of the QD size dispersion, is theoretically studied. Within the framework of effective mass approach, the analytical expression for the light impurity magneto-optical absorption coefficient for both the longitudinal and transversal polarizations with respect to the direction of external quantizing magnetic field is calculated.
Time-resolved magneto-optical Kerr effect (MOKE) and Brillouin light scattering (BLS) spectroscopy are important techniques for the investigation of magnetization dynamics. Within this article, we calculate analytically the MOKE and BLS signals from prototypical spin-wave modes in the ferromagnetic layer. The reliability of the analytical expressions is confirmed by optically exact numerical calculations. Finally, we discuss the dependence of the MOKE and BLS signals on the ferromagnetic layer thickness.
A monolayer of CrI3 has an amazing ferromagnetic ground-state. In this work, we calculate band structures and magnetic moments of tensile-strained and bent zigzag CrI3 nanoribbons with density functional theory. The edge iodine atoms form flat low-lying conduction bands and couple with chromium atoms ferromagnetically, while the non-edge iodine atoms weakly couple antiferromagnetically. CrI3 nanoribbons have a nearly equal preference for the out-of-plane and in-plane magnetic moment configurations, slightly favoring the in-plane one. We also calculate optical absorption with many-body perturba…
Magneto-optical imaging and magnetization measurements were applied to investigate local formation of superconducting phase effected by a random neck synthesis in Y-Ba-Cu-O system. Polished pellets of strongly inhomogeneous ceramic samples show clearly the appearance of superconducting material in the intergrain zones of binary primary particles reacted under different conditions. Susceptibility measurements allows evaluation of superconducting critical temperature, which turned out to be close to that of optimally doped YBCO.
Optical anisotropy is usually treated as an unfavorable condition for the magneto-optical measurements since it is known to diminish the Faraday rotation concerning the case of the isotropic medium. Here we show that the situation could be quite opposite: a phenomenon of birefringence mediated enhancement of the magneto-optical activity appears if the incident light polarization and angle of incidence are set properly. The present study relies on the experimental, analytical, and numerical studies of iron borate $\mathrm{FeBO_3}$ crystals. We demonstrate a significant increase of the magneto-o…
We report on magnetization precession induced in (Ga,Mn)As by an optical spin transfer torque (OSTT). This phenomenon, which corresponds to a transfer of angular momentum from optically-injected spin-polarized electrons to magnetization, was predicted theoretically in 2004 and observed experimentally by our group in 2012. In this paper we provide experimental details about the observation of OSTT by a time-resolved pump-and-probe magneto-optical technique. In particular, we show that the precession of magnetization due to OSTT can be experimentally separated from that induced by the well known…
High-resolution magnetostriction measurement of $ΔL/L\sim10^{-6}$ at a speed of 5 MHz is performed, using optical filter method as the detection scheme for the fiber Bragg grating (FBG) based strain monitor is performed under 35-millisecond pulsed high magnetic fields up to 45 T at 2.2 K. The resolution of magnetostriction is about the same order as the conventionally reported value from FBG based magnetostriction measurement systems for millisecond pulsed magnetic fields. The measurement speed is $\sim$100 times the conventional ones. Present system can be a faster alternative for the convent…
Magneto-optical properties of ZnO:Co and ZnO:Ni films were measured. Magnetization measurements show that some of the films are paramagnetic and others are ferromagnetic. Magnetic circular dichroism clarified that Zn1-xCoxO and Zn1-xNixO included in samples are paramagnetic diluted magnetic semiconductors. Ferromagnetic precipitations seem to be responsible for the observed ferromagnetic behaviors. Criteria to judge the ferromagnetic DMS are also discussed.
Excitation of a metallic ferromagnet such as Ni with an intensive femtosecond laser pulse causes an ultrafast demagnetization within approximately 300 fs. It was proposed that the ultrafast demagnetization measured in femtosecond magneto-optical experiments could be due to relativistic light-induced processes. We perform an ab initio investigation of the influence of relativistic effects on the magneto-optical response of Ni. To this end, we develop, first, a response theory formulation of the additional appearing ultra-relativistic terms in the Foldy-Wouthuysen transformed Dirac Hamiltonian d…
We report on a theoretical study of the electronic, optical and magneto-optical properties of digital ferromagnetic hetero-structures based on $Mn$ $δ$--doped $GaAs$. We consider different structures corresponding to $Mn$ contents within the range 12-50\% and we study how the system changes as a function of the doping concentration. Our first--principles approach includes the spin-orbit interaction in a fully relativistic pseudopotential scheme and the local fields effect in the description of the optical absorption. We show that $Mn$ $δ$-doped $GaAs$ shares many properties with the uniformly …
Three-dimensional topological insulator films in contact with magnetic layers exhibit intriguing magneto-optical and magnetoelectric phenomena, but little is known beyond the linear response regime. We demonstrate that the presence of two electric fields parallel to the surface of the film induces a perpendicular AC polarization, whereas a static polarization can be induced by applying a single circularly polarized electromagnetic wave. These phenomena are determined by the second-order susceptibility, which also controls the manner in which the anomalous Hall current is modulated by a perpend…
It is argued that the non-collinear orbital magnetism accompanying the orthorhombic distortion is an important ingredient which should be taken into consideration for making promising materials with the best magneto-optical characteristics on the basis of SrRuO$_3$.
A magnetization-induced rotation in the third-order nonlinear optical response is observed in out-of-plane-magnetized epitaxial EuO films. We discuss the relation of this nonlinear magneto-optical rotation to the linear Faraday rotation. It is allowed in all materials but, in contrast to the linear Faraday rotation, not affected by the reduction of the thickness of the material. Thus, the third-order magneto-optical rotation is particularly suitable for probing the magnetization of functional magnetic materials such as ultra-thin films and multilayers.
We demonstrate a ten-fold resonant enhancement of magneto-optical effects in perpendicularly magnetized $[$Co/Pt$]_{N}$ nanodots mediated by the excitation of optimized plasmon modes. Two magnetoplasmonic systems are considered; square arrays of $[$Co/Pt$]_{N}$ nanodots on glass and identical arrays on a Au/SiO2 bilayer. On glass, the optical and magneto-optical spectra of the nanodot arrays are dominated by the excitation of a surface lattice resonance (SLR), whereas on Au/SiO${}_{2}$, a narrow surface plasmon polariton (SPP) resonance tailors the spectra further. Both the SLR and SPP modes a…
Here, we study the magneto-optical interactions in magnetic structures considering the dependence of the interactions with the magnetic field. We perform numerical simulations in a structure of magnetic nanowires, considering them as one chain of strongly interacting single-domain particles. Robustly, we obtain a quantitative value for the interactions, which allows us to classify them into two magnetic states: demagnetized and magnetized.
We exploit theoretically a magneto-controlled nonlinear optical material which contains ferromagnetic nanoparticles with a non-magnetic metallic nonlinear shell in a host fluid. Such an optical material can have anisotropic linear and nonlinear optical properties and a giant enhancement of nonlinearity, as well as an attractive figure of merit.
Electrodynamic responses from three-dimensional (3D) topological insulators (TIs) are characterized by the universal magnetoelectric $E\cdot B$ term constituent of the Lagrangian formalism. The quantized magnetoelectric coupling, which is generally referred to as topological magnetoelectric (TME) effect, has been predicted to induce exotic phenomena including the universal low-energy magneto-optical effects. Here we report the experimental demonstration of the long-sought TME effect, which is exemplified by magneto-optical Faraday and Kerr rotations in the quantum anomalous Hall (QAH) states o…
Rapid developments in material research of metallic ferromagnetic (III,Mn)V semiconductors over the past few years have brought a much better understanding of these complex materials. We review here some of the main developments and current understanding of the bulk properties of these systems within the metallic regime, focusing principally on the magneto-transport and magneto-optical properties. Although several theoretical approaches are reviewed, the bulk of the review uses the effective Hamiltonian approach, which has proven useful in describing many of these properties namely in (Ga,Mn)A…
Magnetic and spintronic media have offered fundamental scientific subjects and technological applications. Magneto-optic Kerr effect (MOKE) microscopy provides the most accessible platform to study the dynamics of spins, magnetic quasi-particles, and domain walls. However, in the research of nanoscale spin textures and state-of-the-art spintronic devices, optical techniques are generally restricted by the extremely weak magneto-optical activity and diffraction limit. Highly sophisticated, expensive electron microscopy and scanning probe methods thus have come to the forefront. Here, we show th…
The magneto-optical properties of simple hexagonal graphite exhibit rich beating oscillations, which are dominated by the field strength and photon energy. The former has a strong effect on the intensity, the energy range of the beating and the number of groups, and the latter modulates the total group numbers of the oscillation structures. The single-particle and collective excitations are simultaneously presented in the magnetoreflectance spectra and can be precisely distinguished. For the loss function and reflectance, the beating pattern of the first group displays stronger intensities and…
The discovery of atomically thin two-dimensional (2D) magnetic semiconductors has triggered enormous research interest recently. In this work, we use first-principles many-body perturbation theory to study a prototypical 2D ferromagnetic semiconductor, monolayer chromium tribromide (CrBr$_3$). With broken time-reversal symmetry, spin-orbit coupling, and excitonic effects included through the full-spinor $GW$ and $GW$ plus Bethe-Salpeter equation ($GW$-BSE) methods, we compute the frequency-dependent layer polarizability tensor and dielectric function tensor that govern the optical and magneto-…
Diagonal and off-diagonal optical conductivity spectra have been determined form the measured reflectivity and magneto-optical Kerr effect (MOKE) over a broad range of photon energy in the itinerant ferromagnetic phase of CuCr$_2$Se$_4$ at various temperatures down to T=10 K. Besides the low-energy metallic contribution and the lower-lying charge transfer transition at $E$$\approx$2 eV, a sharp and distinct optical transition was observed in the mid-infrared region around $E$$=$0.5 eV with huge magneto-optical activity. This excitation is attributed to a parity allowed transition through the S…
Magneto-optical Kerr effect (MOKE) is an efficient approach to probe surface magnetization in thin film samples. Here we present a wide-field MOKE technique that adopts a K$ö$hler illumination scheme to characterize the current-induced damping-like spin-orbit torque (DL-SOT) in micronsized and unpatterned magnetic heterostructures with perpendicular magnetic anisotropy. Through a current-induced hysteresis loop shift analysis, we quantify the DL-SOT efficiency of a Ta-based heterostructure with bar-shaped geometry, Hall-cross geometry, and unpatterned geometry to be $|ξ_{DL}|\approx$ 0.08. The…
The magneto-optical spectra of NiMnSb were calculated in the framework of the Local Spin Density Approximation (LSDA) combined with Dynamical Mean-Field Theory (DMFT). Comparing with results based on plain LSDA, an additional account of many-body correlations via DMFT results in a noticably improved agreement of the theoretical Kerr-rotation and ellipticity spectra with corresponding experimental data.
Considerable research interest has been attracted to noncollinear magnetic structures for their intriguing physics and promising applications. In this work, based on relativistic density functional theory, we reveal the interesting magnetic order and relevant properties in monolayer RuF$_4$, which can be exfoliated from its bulk phase. Although the spins on Ru ions are almost antiferromagnetically aligned between nearest-neighbors, weak ferromagnetism is generated because of the antisymmetric Dzyaloshinskii-Moriya interaction as well as the single-ion anisotropy. A prominent magneto-optical Ke…
Magneto-optic behaviour is a specific, non-reciprocal example of gyrotropic behaviour. When coupled to photo-induced Faraday rotation it is possible to discriminate this effect from the background of other nonlinear effects Non-reciprocal behaviour is characteristic of artificial gyrotropy and can be used in optical isolators and a range of coherence and quantum problems. This is all in sharp contrast to natural gyrotropy, like optical activity. it is also important to go beyond third-order, Kerr, optical nonlinearity and move towards a saturable model of terms in the polarisation. In this spi…
A mechanism is proposed based on the Kubo formula to generate a spin-polarized magneto-optical current of Dirac electrons in solids which have strong spin-orbit interactions such as bismuth. The ac current response functions are calculated in the isotropic Wolff model under an external magnetic field, and the selection rules for Dirac electrons are obtained. By using the circularly polarized light and tuning its frequency, one can excite electrons concentrated in the spin-polarized lowest Landau level when the chemical potential locates in the band gap, so that spin-polarization in the magneto…
