Giant Magneto-optical Effect Research Articles

Giant magneto-optical Kerr effects governed by the quasi-bound states in the continuum

The magneto-optical Kerr effect (MOKE), as one of the magneto-optical effects, exhibits polarization change upon reflection that can be used to explore the internal information of magnetic materials with broad applications in modern information technology. However, typically, MOKE is quite weak due to the lower magneto-optical interaction. To tremendously enhance the MOKE, quasi-bound states in the continuum in a one-dimensional Ce- doped Y3Fe5O12 (CeYIG) film photonic crystal slabs (PCS) are proposed to improve the magneto-optical interaction in this work. A giant enhancement in the rotation angle and ellipticity of the longitudinal MOKE, which is about 93.4 and 136.8 times stronger than a pure uniform CeYIG, can be realized. Almost circularly polarized reflected beams with different chiralities are obtained with the CeYIG film. By tuning the geometric parameters of the PCS and the applied external magnetic field, dynamic control of polarization states of the reflected beams with different wavelengths can be realized. This magneto-optical metasurface provides a convenient way for the implementation of magneto-optical devices such as information memory devices, sensors, polarizers, and chiral devices.

Advances in magneto-optical birefringence effect of 2D materials with extremely large aspect ratio

Achieving giant magneto-optical birefringence is a long-standing goal in view of its intriguing physics and potential applications in transmitted light modulation. Due to the unique geometric features of two-dimensional materials with extremely large shape anisotropy, the resultant couplings among magnetic, electric, and optical properties enable giant magneto-optical birefringence effects, as represented by a record-breaking magneto-optical Cotton–Mouton coefficient in two-dimensional material systems. In this Perspective, we introduce the discovery of the giant magneto-optical birefringence effect in two-dimensional metal oxide dispersion in 2020, followed by analyses of the underlying mechanisms. We then discuss how the interplay of anisotropy and colloidal behavior affects the Cotton–Mouton effect. Finally, we proceed to potential applications and give our ideas about future developments in this emerging field.

Topological Co3Sn2S2 magnetic Weyl semimetal: From fundamental understanding to diverse fields of study

A wider scope in topological semimetals accelerates various attractive quantum phenomena for the last two decades. We here report the detailed investigation of magnetic Co 3 Sn 2 S 2 Weyl semimetal based on the cobalt accompanied kagome lattice for the first time. We emphasize the highly motivated theoretical and experimental analyses in each topological terms of Co 3 Sn 2 S 2 that led to intensifying emergent topological materials with inherent properties, particularly in the pursuance of magnetic rich quantum anomalous Hall effect. We additionally highlight the Co 3 Sn 2 S 2 surface band structure, recognized in the diverse fields of study from the perception of topological properties to modern electrochemistry approaches. From materials perspective, this typical kagome Co 3 Sn 2 S 2 Weyl semimetal alone has extensively covered more enriching nontrivial surface states than topological insulators and nonmagnetic semimetals even in the absence of magnetic field and external strain. Some specific examples include Weyl nodes linked flat band magnetism, a large anomalous Hall effect, anomalous Hall angle, giant magnetooptical effect, and thermomagnetic Nernst effect. In addition, we selectively extend the review on the undisputed surface band characteristics of Co 3 Sn 2 S 2 , by which a major concept of magnetic Weyl semimetal could hierarchically meet the contemporary quantum phenomena. This strongly led to more focus on nontrivial magnetic topological studies for gaining insightful perspectives.

Magnetic nanocomposite films with photo-patterned 1D grating on top enable giant magneto-optical intensity effects

The enhancement of magneto-optical (MO) effects in planar devices is commonly obtained through the combination of a plasmonic resonance and a MO material, or through the microstructuration of such materials. However, the devices often suffer from weak optical signal, or require fastidious lithography processes. We present a much simpler device made of a photoresist 1D grating processed on a MO composite planar waveguide. This latter is formed by magnetic nanoparticles embedded in a silica matrix. Such all-dielectric device produces much higher Q-factor resonances, which finally result in giant MO intensity effects. Their magnitude combined with the ability of the device to be processed on large scale and various substrates, are very promising for a wide range of sensing applications.

Giant magneto-optical rotation effect in rubidium vapor measured with a low-cost detection system

With substantial improvements on the optical arrangement, we show that significant enhancement of the magneto-optical rotation effect in rubidium vapor can be achieved without using complex and expensive heterodyne polarimetric methods. The huge signal-to-noise ratio performance using low cost photo-detectors opens the door to chip-sized device manufacturing and in-situ applications in biomagnetism.

Giant magneto-optical Faraday effect of graphene on Co in the soft x-ray range

Using polarization analysis of linearly polarized synchrotron radiation we demonstrate the existence of a giant magneto-optical Faraday effect at the carbon $1s$ edge of single-layer graphene on Co, reaching Faraday rotation angles of $2.9\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.16em}{0ex}}\mathrm{deg}/\mathrm{mm}$. This value is of the order of those observed at the Co $3p$ and $2p$ edges. Using element-selective magnetic hysteresis curves we find that graphene on Co exhibits ferromagnetic order. The magnetism in graphene is found to be carried by and be strongly enhanced by aligned \ensuremath{\pi} orbitals of carbon atoms. It is induced by hybridization with the Co $3{d}_{z}2$ orbitals while carbon \ensuremath{\sigma} bonds show negligible magnetism due to insignificant hybridization with Co. From additional x-ray magnetic circular dichroism and transversal magneto-optical Kerr effect spectra a magnetic moment of $0.14\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ is estimated for graphene. From Faraday spectra the complete set of x-ray magneto-optical constants of graphene has been deduced which allows for future modeling of magneto-optical devices based on graphene. The strong magnetism in graphene results from hybridization of carbon ${p}_{\mathrm{z}}$ and metal $3d$ orbitals. Atoms of the graphene sublattice A, placed on top of Co, lead to strongest hybridization with Co $3{{d}_{z}}^{2}$ orbitals. Carbon atoms of sublattice B, and those of rotated graphene domains without Co atoms beneath, hybridize with each other and with $3{d}_{\mathrm{xz}}$ and $3{d}_{\mathrm{yz}}$ orbitals of neighboring Co atoms forming tilted ${p}_{\mathrm{z}}$ bonds. We show that the related reduction of A-B symmetry leads to a splitting of the spin-polarized density of conduction-band states which is responsible for the strong magneto-optical Faraday effect.

Nonreciprocal Giant Magneto-Optic Effects in Transition-Metal Dichalcogenides without Magnetic Field.

Magnetic exchange field has been demonstrated to be effective in enhancing the valley splitting of monolayer transition-metal dichalcogenides experimentally. However, how magnetic exchange coupling affects the magnetooptical behaviors in massive Dirac systems remains elusive. Using k⃗·p⃗ model and Kubo formula, we theoretically report that optical Hall conductivity and giant magnetooptical effects can be induced in monolayer transition-metal dichalcogenides even if there is no any magnetic field involved when considering magnetic exchange interaction. Such an unusual result originates from the fact that the existence of magnetic exchange coupling effectively enables the breaking of time reversal symmetry, which grants the removal of valley degeneracy and unveils the possibility of generation and manipulation of magnetooptical effects in monolayer transition-metal dichalcogenides with no need for magnetic field. Our results suggest that the presence of magnetic exchange coupling of transition-metal dichalcogenides represents an alternative strategy capable of inducing magnetoopitcal effects, which can be extended to other monolayer massive Dirac systems.

Giant magneto-optical Raman effect in a layered transition metal compound

We report a dramatic change in the intensity of a Raman mode with applied magnetic field, displaying a gigantic magneto-optical effect. Using the nonmagnetic layered material MoS2 as a prototype system, we demonstrate that the application of a magnetic field perpendicular to the layers produces a dramatic change in intensity for the out-of-plane vibrations of S atoms, but no change for the in-plane breathing mode. The distinct intensity variation between these two modes results from the effect of field-induced broken symmetry on Raman scattering cross-section. A quantitative analysis on the field-dependent integrated Raman intensity provides a unique method to precisely determine optical mobility. Our analysis is symmetry-based and material-independent, and thus the observations should be general and inspire a new branch of inelastic light scattering and magneto-optical applications.

Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals.

Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn(2+), Co(2+) and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large Beff that exist in Mn(2+)-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ∼ 15 -30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn(2+) moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.

Giant magneto-optical Faraday effect in GaP epilayers containing MnP magnetic nanoclusters

We report a giant magneto-optical (MO) effect in a GaP(011) epilayer with embedded MnP nanoclusters (GaP:MnP) grown on a GaP(011) substrate using metal-organic vapor phase epitaxy. The MO effect exhibits a hysteretic behavior when sweeping the applied magnetic field, thereby indicating a clear dependence upon the magnetization of the sample. The measured Faraday rotation per unit length is 60 times higher in the epilayer than that of GaP at room temperature. The role of the magnetization in the MO effect makes it possible to increase this factor even further by lowering the temperature well below the Curie point (TC) of 292 K for those samples. We observed an increase of the Faraday rotation at longer wavelengths, indicating that those GaP:MnP epilayers could potentially be useful for enhanced MO effects in the visible and infrared regions of the electromagnetic spectrum.

Properties of the Photonic Hall Effect in Cold Atomic Clouds

On the basis of exact numerical simulations and analytical calculations, we describe qualitatively and quantitatively the interference processes at the origin of the photonic Hall effect for resonant Rayleigh (point-dipole) scatterers in a magnetic field. For resonant incoming light, the induced giant magneto-optical effects result, even for magnetic field strength as low as a few mT, in relative Hall currents in the percent range. This suggests that the observation of the photonic Hall effect in cold atomic vapors is within experimental reach.

Giant Magneto-Optical Kerr Effects in Ferromagnetic Perovskite BiNiO3 with Half-Metallic State

We theoretically show that the giant magneto-optical Kerr effects are induced by the electronic structure of half-metallic ferromagnetism in the perovskite BiNiO3 with the orthorhombic structure by first-principles calculation. A Kerr rotation is up to 1.28° at 1.87 eV, which is comparative to the recognized maximum polar Kerr rotation of 1.35° at 1.75 eV in the Heusler compound PtMnSb. The strong p−d exchange interaction causes the half-metallic ferromagnetism, i.e., the majority-spin electrons are semiconducting and the minority-spin electrons are metallic, which finally leads to the large Kerr rotation in the half-metallic ferromagnetic perovskite BiNiO3.

Giant magneto-optical faraday effect of nanometer Fe-In2O3 granular films

The giant magneto-optical Faraday effect of nanometer ferromagnetic metal-semiconductor matrix Fe-In2O3 granular films prepared by the radio frequency sputtering are studied. The result shows that the Faraday rotation angle θF value of the granular film samples with Fe volume fraction x = 35% is of the order of 105(°)/cm at room temperature. Temperature dependence of the Faraday rotation angle θF of Fe0.35(In2O3)0.65 granular films shows that θF value below 10 K increases rapidly with the decrease of the temperature, and when T = 4.2 K, θF value is 106(°)/cm. Through the study of the dependence of low field susceptibility on temperature and the hysteresis loops at different temperatures, it has been found that when the temperature decreases to a critical point TP = 10 K, the transformation of state from ferromagnetic to spin-glass-like occurs in Fe0.35(In2O3)0.65 granular films. The remarkable increase of the Faraday rotation angle θF value of Fe0.35(In2O3)0.65 granular films below 10 K seems to arise from the sp-d exchange interaction of the granular film samples in the spin-glass-like state.

Giant Faraday rotation in Fe–ZnSe granular films

The giant magneto-optical Faraday effect (giant Faraday rotation) of ferromagnetic metal–semiconductor matrix Fe–ZnSe granular films prepared by radio frequency sputtering is studied. The result shows that the Faraday rotation angle θ F value of the granular films sample with Fe volume fraction x=35% is of the order of 10 5 °/cm at room temperature. Temperature dependence of the θ F of Fe 0.35(ZnSe) 0.65 granular films shows that θ F value, below 150 K, increases rapidly with the decrease of the temperature, and when T=10 K θ F value is 6×10 5 °/cm. Through the study of the structure and dependence of magnetic properties on temperature, it has been found that the remarkable increase of the θ F value of Fe 0.35(ZnSe) 0.65 granular films below 150 K seems to arise from the sp–d exchange interaction inside the granular films.

Josephson vortex lattices as scatterers of terahertz radiation: Giant magneto-optical effect and Doppler effect using terahertz tunable photonic crystals

The Josephson vortex (JV) lattice generated by the in-plane magnetic field ${H}_{ab}$ is a periodic array that scatters Josephson plasma waves (JPWs) in layered superconductors. This produces a photonic band gap structure, i.e. terahertz (THz) photonic crystal, with easily tunable forbidden zones, or gaps, controlled either by the in-plane magnetic field or the transverse transport current ${J}_{\ensuremath{\perp}}$ flowing across the superconducting layers. A giant magneto-optical effect, that is a strong dependence of the reflection and transmission coefficients on the applied in-plane magnetic field ${H}_{ab}$, is predicted. A relatively small change of ${H}_{ab}$ can switch the sample from fully transparent to fully reflective within given frequency windows. Thus, the material can change from a THz glass to a mirror by merely changing either ${H}_{ab}$ or ${J}_{\ensuremath{\perp}}$. The described effects might be useful for development switchable ``glass/mirrors'' THz filters tuned by either ${H}_{ab}$ or ${J}_{\ensuremath{\perp}}$.

Nano-Optics on Individual Quantum Objects - From Single to Coupled Semiconductor Quantum Dots

Some recent highlights of our optical studies on single and coupled semiconductor quantum dots are reviewed. In the first part, we concentrate on the role of spins and spin-spin interaction in nonmagnetic and magnetic single quantum dots. In the case of strictly resonant excitation of the ground state in self-assembled CdSe/ZnSe quantum dots, we find an exciton spin relaxation time, which exceeds the recombination lifetime significantly. Linear polarization has to be used for these experiments, as the electron-hole exchange interaction lifts the spin degeneracy and the eigenstates are linear combinations of spin-up and spin-down excitons. In a magnetic quantum dot, the exchange interaction between carrier spins and the spins of magnetic ions is shown to be responsible for giant magneto-optical effects. We demonstrate the formation of zero-dimensional magnetic polarons and we succeeded in measuring the magnetization on a scale of a few nanometers using the characteristic photoluminescence signal of individual quantum dots as experimental monitor. The second part is devoted to pairs of single quahtum dots. On one hand, single exciton tunneling within an individual quantum dot pair is demonstrated studying single pairs of vertically correlated strain-induced and self-organized quantum dots. On the other hand, we show that in a pair of lithographically defined single dots with strongly different g-factors the energy spacing between the dot ground states can be tuned in an external magnetic field by about 10 meV, giving access to a controlled coupling between two individual quantum dots.

Enchanced magnetooptical response of magnetic nanoclusters embedded in semiconductor

In the present work, we report the results of an experimental study of magnetooptical Kerr effect and optical properties in MnAs:GaAs granular films in the spectral range 0.5–4.5 eV at room temperature and at 4.2 K. The possible mechanisms of the giant magnetooptical effect in MnAs:GaAs granular films are discussed on the basis of the obtained results.

Magneto-optical properties and the potential application of GaAs with magnetic MnAs nanoclusters

The giant magneto-optical effect of ferromagnetic MnAs nanoclusters embedded in GaAs is shown. The Faraday rotation angle at 0.98 μm reaches about 0.2°/μm at 2000 Oe. The potential of this magneto-optical material for use as a Faraday rotator operating at 0.98 μm is demonstrated by the Verdet constant of the film which is 16 times larger than that of (Cd,Mn,Hg)Te commercially developed for an optical isolator. The fabrication of this material is compatible with that of semiconductor-based devices.

Giant magneto-optical effects in diluted magnetic semiconductor nanostructures

Nanostructures of diluted magnetic semiconductors show varieties of optical phenomena caused by the interaction of electrons and holes with magnetic ions in the confined electronic states. We present giant magneto-optical effects and ultrafast exciton dynamics in two-dimensional quantum wells of the Cd 1− x Mn x Te/ZnTe system and quantum dots of Cd 1− x Mn x Se.

Structure and Giant Magneto-Optical Effect of MnSbPt Films

MnSbPt films containing 50 at%Mn, 44 at%Sb, and 6 at% Pt were prepared by RF sputtering. XRD, TEM, and NMR studies revealed that in the as-deposited state, MnSbPt films had a disordered hexagonal structure, and that after annealing at 300°C NiAs-type structure and an fee-type structure were formed, promoting phase separation in MnSbPt films with a giant magneto-optical Kerr rotation. The assumption of a two-phase mixture of NiAs and fee structures is difficult to explain the giant magneto-optical effect in the short wevelength region (∼500 nm) for MnSbPt films. The giant magneto-optical effect is thought to be associated with the microstructure due to the phase separation process.