Magneto-optical Faraday Effect Research Articles

Properties of CoPt ferromagnetic layers for application in spin light-emitting diodes

The magnetic properties of Co45Pt55 films deposited by electron-beam evaporation in vacuum have been studied. The measurements of the Faraday and Kerr magnetooptical effects confirm the presence of the easy-magnetization axis perpendicular to the Co45Pt55 surface. It is shown that the perpendicular magnetic anisotropy and the residual magnetization are retained at 300 K for a long time. The magnetic characteristics of the Co45Pt55 layer surface have been studied by magnetic force microscopy, and “circular” mobile magnetic structures have been detected. The spin light-emitting diodes based on In(Ga)As/GaAs heteronanostructures with Co45Pt55 contact layers were fabricated. These diodes emit circularly-polarized light in the absence of an external magnetic field.

Colossal magneto-optical modulation at terahertz frequencies by counterpropagating femtosecond laser pulses in Tb3Ga5O12.

Single-frequency terahertz modulation of the magneto-optical Faraday effect with a record amplitude of the polarization rotation of ∼0.5° is achieved using a slab of the etalon Faraday rotator crystal Tb3Ga5O12. The modulation is the result of the interaction of two counterpropagating laser pulses via the optical Kerr effect. The frequency of the modulation is determined by the applied magnetic field and is continuously tunable in a terahertz frequency range between 0 and 0.7THz.

Development of a magneto-optical sensor prototype to measure current by means of the induced magnetic field

The design and construction of the working prototype of a device to measure the magnetic field induced by a conducting wire as well as the current that induces this field, based on the magneto-optical Faraday effect, is described in this work. The transducer element is a nanocomposite material made up of maghemite nanoparticles embedded in a porous silica matrix, with a high low-field Verdet constant and a figure of merit, relating Faraday specific rotation to the absorption coefficient, of 5. The device has been mostly developed with low-cost parts, using the open-source prototyping platform Arduino plus a compact commercial lock-in amplifier. It is shown that the sensing material shows a linear response up to 30G, which would allow measuring AC currents of 1300A at ∼10cm from the wire. This setup allows avoiding the use of any magnetic field concentrator.

Optical fiber current sensor research: review and outlook

Optical fiber current sensor (OFCS) based on Faraday magneto-optic effect has many advantages of immunity against electromagnetic interference, high sensitivity and wide dynamic range. Thus, OFCS has extensive application prospects. In this paper, the authors present a review on OFCS. The basic principle of OFCS is firstly discussed. And then the main advantages and disadvantages of several common types of OFCS are compared. On this basis, the effect of the linear birefringence on OFCS is discussed emphatically. Moreover, the research results about the linear birefringence measurement and suppression methods are summarized. In the end, the future research direction of OFCS is presented, which will provide ideas for subsequent research work.

Transient Grating Spectroscopy in Magnetic Thin Films: Simultaneous Detection of Elastic and Magnetic Dynamics.

Surface magnetoelastic waves are coupled elastic and magnetic excitations that propagate along the surface of a magnetic material. Ultrafast optical techniques allow for a non-contact excitation and detection scheme while providing the ability to measure both elastic and magnetic components individually. Here we describe a simple setup suitable for excitation and time resolved measurements of high frequency magnetoelastic waves, which is based on the transient grating technique. The elastic dynamics are measured by diffracting a probe laser pulse from the long-wavelength spatially periodic structural deformation. Simultaneously, a magnetooptical measurement, either Faraday or Kerr effect, is sensitive to the out-of-plane magnetization component. The correspondence in the response of the two channels probes the resonant interaction between the two degrees of freedom and reveals their intimate coupling. Unraveling the observed dynamics requires a detailed understanding of the spatio-temporal evolution of temperature, magnetization and thermo-elastic strain in the ferromagnet. Numerical solution of thermal diffusion in two dimensions provides the basis on which to understand the sensitivity in the magnetooptic detection.

Large Faraday rotation in magnetophotonic crystals containing SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles

This paper has focused on the potential of the SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles in order to achieve the high performance one-dimensional magnetophotonic crystals (MPCs) and to overcome the problem of integration of the magneto-optical devices. Because of importance of magneto-optical Faraday effect in most non-reciprocal optical components, we have investigated the capability of such silicon-based materials for providing large Faraday rotations. We have introduced some MPC structures containing SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles and by varying the concentration of magnetic nanoparticles, influence of volume fraction VF% on the Faraday rotation and transmittance of the structures has studied.

Local probing of magnetic films by optical excitation of magnetostatic waves

Excitation of volume and surface magnetostatic spin waves in ferrite garnet films by circularly polarized laser pulses utilizing to the inverse magnetooptical Faraday effect has been studied experimentally. The region of excitation of the magnetostatic spin waves is determined by the diameter of the laser beam (∼10 μm). At the same time, the characteristic propagation length of the modes is 30 μm. A method of finding the local characteristics of a magnetic film, in particular, the cubic and uniaxial anisotropy constants, based on the analysis of the azimuthal-angle dependence of the spectrum of the magnetostatic spin waves has been proposed.

Study on the properties of photonic band gap and flatbands in the three-dimensional magnetized plasma photonic crystals with a general case

In this paper, the properties of photonic band gap (PBG) and flatbands in the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with a general case in face-centered-cubic lattices are theoretically investigated based on the modified plane wave expansion method, in which the homogeneous magnetized plasma spheres are immersed in the homogeneous and isotropic dielectric background, as the magneto-optical Faraday effects are considered. The more general situation has been considered, and the PBG of such MPPCs is for all of the electromagnetic waves. The derivation of the formulas for calculating also is given. Theoretical computing results show that a PBG and two flatbands regions can be obtained. Compared to the conventional dielectric-air photonic crystals with similar structure, the larger PBG can be obtained in such 3D MPPCs. However, the narrower PBG can be achieved compared to that for the right circular polarized (RCP) wave, and the larger upper edge frequency of second flatbands region can be achieved. For the flatbands region, the upper edge only can be tuned by the plasma frequency and plasma cyclotron frequency. The effects of plasma frequency and plasma cyclotron frequency (the external magnetic field) on the properties of PBG also are investigated theoretically in detail. Theoretical simulations show that the PBG can be manipulated by those two parameters. The results show that the properties of PBG are obviously different with those for RCP wave in the similar 3D MPPCs. Those results can hold promise for opening a new scope to design the filters, planar reflectors, omnidirectional mirrors, absorber or waveguides based on the 3D MPPCs.

Advanced magneto-optical microscopy: Imaging from picoseconds to centimeters - imaging spin waves and temperature distributions (invited)

Recent developments in the observation of magnetic domains and domain walls by wide-field optical microscopy based on the magneto-optical Kerr, Faraday, Voigt, and Gradient effect are reviewed. Emphasis is given to the existence of higher order magneto-optical effects for advanced magnetic imaging. Fundamental concepts and advances in methodology are discussed that allow for imaging of magnetic domains on various length and time scales. Time-resolved imaging of electric field induced domain wall rotation is shown. Visualization of magnetization dynamics down to picosecond temporal resolution for the imaging of spin-waves and magneto-optical multi-effect domain imaging techniques for obtaining vectorial information are demonstrated. Beyond conventional domain imaging, the use of a magneto-optical indicator technique for local temperature sensing is shown.

Enhancement of magneto-optical Faraday effects and extraordinary optical transmission in a tri-layer structure with rectangular annular arrays.

The properties of optics and magneto-optical Faraday effects in a metal-dielectric tri-layer structure with subwavelength rectangular annular arrays are investigated. It is noteworthy that we obtained the strongly enhanced Faraday rotation of the desired sign along with high transmittance by optimizing the parameters of the nanostructure in the visible spectral ranges. In this system, we obtained two extraordinary optical transmission (EOT) resonant peaks with enhanced Faraday rotations, whose signs are opposite, which may provide the possibility of designing multi-channel magneto-optical devices. Study results show that the maximum of the figure of merit (FOM) of the structure can be obtained between two EOT resonant peaks accompanied by an enhanced Faraday rotation. The positions of the maximum value of the FOM and resonant peaks of transmission along with a large Faraday rotation can be tailored by simply adjusting the geometric parameters of our models. These research findings are of great importance for future applications of magneto-optical devices.

Terahertz modulation of the Faraday rotation by laser pulses via the optical Kerr effect

Terbium gallium garnet is used to demonstrate a new approach to magneto-optical modulation at frequencies up to 1.1 THz. The magneto-optical Faraday effect played a crucial role in the elucidation of the electromagnetic nature of light. Today it is powerful means to probe magnetism and the basic operational principle of magneto-optical modulators. Understanding the mechanisms allowing for modulation of the magneto-optical response at terahertz frequencies may have far-reaching consequences for photonics1, ultrafast optomagnetism2,3,4 and magnonics5,6, as well as for future development of ultrafast Faraday modulators. Here we suggest a conceptually new approach for an ultrafast tunable magneto-optical modulation with the help of counter-propagating laser pulses. Using terbium gallium garnet (Tb3Ga5O12) we demonstrate the feasibility of such magneto-optical modulation with a frequency up to 1.1 THz, which is continuously tunable by means of an external magnetic field. Besides the novel concept for ultrafast magneto-optical polarization modulation, our findings reveal the importance of accounting for propagation effects in the interpretation of pump–probe magneto-optical experiments.

Terahertz spin-wave waveguides and optical magnonics in one-dimensional NiO nanorods.

The two-magnon (2M) spin waves with a magnon frequency of 43 THz, generated by a polarized laser, were first observed in one-dimensional (1D) NiO nanorods. The 1D NiO nanorods of ∼700 nm length, which have perfectly in-plane antiferromagnetic spins lying on the (200) and (100) faces, are the smallest spin-wave waveguides. Due to the magneto-optical Faraday effect (MOFE), the significant change in the Faraday intensity can show the 2M information in the NiO nanorods. There are only two 2M-on and 2M-off states at various applied alternating-current magnetic fields and laser-incident angles, which make the 1D NiO nanorods excellent optical nanomagnonics.

Modeling for detecting micro-gap weld based on magneto-optical imaging

A new method based on Faraday magneto-optical effect to detect micro-gap weld whose width is less than 0.1mm in a butt joint laser welding is developed. The characteristics of magneto-optical images and magnetic field distribution reflecting the weld position are analyzed. An electromagnet exciter is adopted to magnetize the carbon steel weldment and establish a leakage magnetic field at the welding joint. Magneto-optical sensor is set over the magnetized weldment to obtain the magneto-optical images. A model based on the magnetic charge theory is proposed to investigate the magnetic field distribution over the welding joint and it is demonstrated by computer simulations and experiments, which show that the midline of welding joint is corresponding to the transitional zone midline in a magnetic-optical image. This model is evaluated by seam tracking experiment and shows that it can effectively and accurately track the micro-gap weld.

Strong Magnetochiral Dichroism in Suspensions of Magnetoplasmonic Nanohelices

We show theoretically that self-assembled metamaterial suspensions of magnetoplasmonic entities in the form of magnetic-nanoparticle helices coiled around plasmonic (gold) nanorods exhibit very strong magnetochiral dichroism that is orders of magnitude higher than in conventional materials exhibiting this phenomenon (liquid molecular systems, anisotropic crystals, and chiral ferromagnets). The large values of the calculated magnetochirality are accompanied by an enhancement of the magneto-optical Faraday effect due to the excitation of surface plasmons at the nanorods as well as by an increase of the structural dichroism imparted from the helicoidal arrangement of the magnetic nanoparticles. However, the reported enhancement of the magnetochiral dichroism does not appear to be a cascade phenomenon of the structural and magnetic circular dichroism as, for example, in solutions of magnetic compounds, but appears as a possible manifestation of the emergence of a surface-plasmon-induced toroidal moment within...

Vectorial magnetometry with second-harmonic generation effect in studies of implantation induced inhomogeneity in garnet films

The magnetization-induced second-harmonic generation (MSHG) effect was applied to study changes of magnetization distribution caused by H2+ ions implantation in magnetic garnet film of (111) symmetry. The evolution of the magnetization vector m in perpendicular magnetic field H was studied as a function of coherently rotated polarizers by an angle φ. The I2ω(H,φ) intensities exhibit completely different character as compared to the unimplanted film. The experimental results were explained in the frame of a phenomenological model of the MSHG effect, developed for the structure of 3m symmetry, composed of implanted and unimplanted sublayers. The theoretical approach allowed to determine the amplitudes and phases of nonlinear optical susceptibility tensor elements χ[2] as well as the m(H) vector components. In contrast to the linear magneto-optical Faraday effect, application of nonlinear MSHG method allows for simultaneous determination of all components of the magnetization vector in single experiment. It ...

Modeling of On-Chip Optical Nonreciprocity with an Active Microcavity

On-chip nonreciprocal light transport holds a great impact on optical information processing and communications based upon integrated photonic devices. By harvesting gain-saturation nonlinearity, we recently demonstrated on-chip optical asymmetric transmission at telecommunication bands with superior nonreciprocal performances using only one active whispering-gallery-mode microtoroid resonator, beyond the commonly adopted magneto-optical (Faraday) effect. Here, detailed theoretical analysis is presented with respect to the reported scheme. Despite the fact that our model is simply the standard coupled-mode theory, it agrees well with the experiment and describes the essential one-way light transport in this nonreciprocal device. Further discussions, including the connection with the second law of thermodynamics and Fano resonance, are also briefly made in the end.

Improving Magnetooptical Faraday Effect of maghemite/silica nanocomposites

The present work is focused on the evaluation and characterization of the Magnetooptical Faraday Effect (MOFE) of sol–gel processed composites consisting of maghemite iron oxide nanoparticles embedded in a silica xerogel matrix. These materials are of great interest mainly for magnetic-field sensing applications because of their high MOFE response, even at low magnetic fields. We have implemented an in-situ approach for the composite processing in which nanoparticles precursor are formed while host matrix polymerization and subsequent annealing steps leads to γ-Fe2O3 nanocrystals growth inside the porous xerogel framework. The samples thus obtained are reddish monoliths showing convenient mechanical properties. This method allows obtaining, with carefully controlled preparation conditions, materials with reproducible mechanical, magnetic and optical properties. It is shown that an additional processing step in which the samples were subjected to thermal oxidation treatment in air, leads to an enhancement more than 10 times in the sample optical transmittance, in comparison with the values of the untreated samples. The study of the magnetooptical behavior of these materials reveals a rather high Faraday rotation, as well as a reproducible and practically reversible linear range at low magnetic fields.

Study on the magneto-optical Faraday effects in the properties of anisotropic photonic band gaps and surface plasmon modes for the three-dimensional magnetized photonic crystals as the mixed polarized waves considered

In this paper, the magneto-optical Faraday effects in the properties of anisotropic photonic band gaps (PBGs) and surface plasmon modes for the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with body-centered cubic lattices are theoretically studied based on the modified plane wave expansion (PWE) method, in which the homogeneous Te (tellurium) spheres are immersed in the homogeneous magnetized plasma background, as the mixed polarized waves are considered. A more general case is investigated, and the anisotropic PBGs are not only for the left- and right-circular polarized waves but also for the mixed polarized waves. The equations for computing those anisotropic PBGs for all of the electromagnetic waves in such 3D MPPCs are theoretically deduced. Theoretical simulations show that the anisotropic PBGs and a flatbands region can be observed. Compared to the similar 3D MPPCs containing the isotropic dielectric or uniaxial material spheres, the largest PBG can be obtained as the extraordinary axis of inserted uniaxial material is along the Г-H symmetry line. The larger PBGs can also be achieved compared to the conventional PBGs for the right-circular polarized wave as the mixed polarized waves are considered. The interesting properties of surface plasmon modes can also be found, which are the upper edge of flatbands region cannot be tuned by the filling factor but almost can be linearly increased with increasing the plasma frequency and plasma cyclotron frequency, respectively. The effects of the filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the anisotropic PBGs are also investigated in detail. Theoretical simulations also show that such PBGs can be manipulated by the parameters as mentioned above.

Resonant Faraday and Kerr effects due to in-gap states on the surface of a topological insulator

When Dirac electrons on the surface of a topological insulator are gapped, the resulting quantum anomalous Hall effect leads to universal magneto-optical Faraday and Kerr effects in the low frequency limit. However, at higher frequencies different excitations can leave their own fingerprints on the magneto-optics and can therefore be probed. In particular, we investigate the role of localized in-gap states---which inevitably appear in the presence of charged impurities---on these higher frequency magneto-optical effects. We have shown that these states resonantly contribute to the Hall conductivity and are magneto-optically active. These in-gap states lead to peculiar resonant signatures in the frequency dependence of the Faraday and Kerr angles, distinct in character to the contribution of in-gap excitonic states, and can be probed in ellipsometry measurements.

Magneto-optical Faraday effect in spin-liquid candidates

We propose an experiment to use the magneto-optical Faraday effect to probe the dynamic Hall conductivity of spin liquid candidates. Theory predicts that an external magnetic field will generate an internal gauge field. If the source of conductivity is in spinons with a Fermi surface, a finite Faraday rotation angle is expected. We predict the angle to scale as the square of the frequency rather than display the standard cyclotron resonance pattern. Furthermore, the Faraday effect should be able to distinguish the ground state of the spin liquid, as we predict no rotation for massless Dirac spinons. We give a semiquantitative estimate for the magnitude of the effect and find that it should be experimentally feasible to detect in both $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ and, if the spinons form a Fermi surface, Herbertsmithite. We also comment on the magneto-optical Kerr effect and show that the imaginary part of the Kerr angle may be measurable.