Magneto-optical Film Research Articles

Structural design of cubic Sr,V:CeFeO3 thin films with a strong magneto-optical effect and high compatibility with a Si substrate.

This paper focuses on strong magneto-optical thin films that closely match a Si substrate. The orthorhombic perovskite crystal structure of CeFeO3 was optimized to a cubic perovskite structure by introducing strontium and vanadium ions into lattice. The cubic Ce1-xSrxFe1-xVxO3 (x = 0.3, 0.5, 0.7) thin films with high quality and high growth orientation were prepared on a Si substrate by using the RF magnetron sputtering method. Moreover, the birefringence effect, which may weaken the magneto-optical effect, should not occur in the cubic thin film. The calculation results based on density functional theory show that the increased electronic transition probability is attributed to the strong spin-coupling between the hybrid Ce3+ 4f and Fe3+/V4+ 3d states. The magnetic circular dichroism ellipticity |ΨF| of the Ce0.7Sr0.3Fe0.7V0.3O3 thin film is up to 4300 deg. cm-1, which indicates a strong magneto-optical effect. Therefore, the cubic Ce1-xSrxFe1-xVxO3/Si film with high Ce3+ concentration is expected to be a new candidate for integrated magneto-optical devices.

Creation of an ultralong non-diffracting magnetization light beam with multiple energy oscillations using the inverse Faraday effect.

Diffraction and scatter effects are two big challenges that make the magnetization induced by a light beam endure a finite propagation distance and vulnerable to the defect of magneto-optic film. Here we propose a method to overcome both challenges by creating an ultralong non-diffracting (UND) magnetization light beam with multiple energy oscillations. By simply increasing the number of energy oscillations using the optical pen, the magnetization light beam can propagate over an ultralong distance without significant divergence. Besides, as a kind of non-diffracting light beam, this magnetization light beam possesses the property of self-healing, which makes it robust to the scatter effect. This Letter demonstrates for the first time, to the best of our knowledge, the creation of an UND magnetization beam, which may open a new avenue for high-density all-optical magnetic recording and atomic trapping, as well as confocal and magnetic resonance microscopy.

Weak measurement of the magneto-optical spin Hall effect of light

The spin Hall effect of light (SHEL) is a photonic version of the spin Hall effect in electronic systems and has been studied for more than 10 years. However, the lack of effective methods for dynamic modulation of spin-dependent splitting may hinder its applications. By introducing additional spin-orbit coupling of photons or nonreciprocal phase shift (NRPS), the magneto-optical Kerr effect may be one of the methods to alleviate the situation. Here, we experimentally reveal an enhanced and tunable SHEL in magneto-optical oxide thin films under the transverse magneto-optical Kerr effect configuration for the first time, to the best of our knowledge, which can be regarded as the magneto-optical SHEL (MOSHEL). We study the magneto-optical response of the multilayer structure and select the optimal structural parameters by the magneto-optical transfer matrix method. With a transverse magnetic field along opposite directions, an obvious SHEL shift difference of H-polarized light caused by NRPS is observed via a weak measurement method. With optimal parameters, the maximum measured shift difference of the SHEL achieves about 70 μm. The demonstrated MOSHEL phenomenon may accelerate the application of the SHEL in the field of spin photonics devices and precision metrology.

Repeatability and stability study of residual magnetic field for domain wall characterization

Residual magnetic field (RMF) for metal material has a relationship with material stress status. Bridging the relationship between macro parameters and material microstructure is an essential step to deal with the characterization of residual stress. This paper applies magneto-optical Kerr microscopy (MOKE) with the help of magneto-optical indicator film (MOIF) to observe and analyze variations of magnetic domain pattern under different stress conditions of high permeability grain oriented electrical steel (HGO steel). Experiment about repeatability is carried under cyclic stress applications and the stability study is proceeded during the relaxation time after release of stress. By using two domain texture features, mean value (MV) of domain wall image intensity linked to domain rotation to characterize RMF amplitude and the angular second moment (ASM) related with domain wall displacement to express the RMF distribution are used for investigation of repeatability and stability. Results show that domain wall displacement is repeatable and stable both under cyclic stress round and during relaxation time after release of stress. It has been found that the situation of domain rotation is varied in different locations, and broad texture area of domain wall images has better repeatability and stability when compared with area with narrow texture of domain wall images. The results provide substantial potential to evaluate the residual stress from the view of characterization of micro-structure.

Monolithic integration of broadband optical isolators for polarization-diverse silicon photonics

Integrated optical isolators have been a longstanding challenge for photonic integrated circuits (PIC). An ideal integrated optical isolator for PIC should be made by a monolithic process, have a small footprint, exhibit broadband and polarization-diverse operation, and be compatible with multiple materials platforms. Despite significant progress, the optical isolators reported so far do not meet all these requirements. In this article we present monolithically integrated broadband magneto-optical isolators on silicon and silicon nitride (SiN) platforms operating for both TE and TM modes with record high performances, fulfilling all the essential characteristics for PIC applications. In particular, we demonstrate fully-TE broadband isolators by depositing high quality magneto-optical garnet thin films on the sidewalls of Si and SiN waveguides, a critical result for applications in TE-polarized on-chip lasers and amplifiers. This work demonstrates monolithic integration of high performance optical isolators on chip for polarization-diverse silicon photonic systems, enabling new pathways to impart nonreciprocal photonic functionality to a variety of integrated photonic devices.

Laser-induced damage of garnet films grown by LPE

Laser-induced damage of magneto-optical (MO) materials is a key factor that limits the application of optical isolators in high-power laser systems. In order to investigate parameters that affecting laser-induced damage thresholds (LIDT) of MO garnet films grown by liquid-phase epitaxial (LPE) method, YIG, (LuBi)3Fe5O12 and (BiTm)3(GaFe)5O12 single crystal films with small lattice mismatch were prepared in this study. The transmittance, optical absorption coefficient, crystal structures, surface quality and laser-induced damage thresholds (LIDT) of the prepared three kinds of MO films were investigated. Microstructure analysis shows that single crystal garnet films grown by LPE method have high surface and crystal quality. Laser-induced damage tests (@1064 nm, 11 ns) pointed out that LIDT of YIG, (LuBi)3Fe5O12 and (BiTm)3(GaFe)5O12 films are 6.41 ± 0.18 J/cm2, 6.32 ± 0.25 J/cm2 and 4.11 ± 0.27 J/cm2, respectively, and intrinsic optical absorption coefficient of single crystal garnet films plays a decisive role in their laser-induced damage.

Specific features of magnetic domain structure in epitaxial magneto-optical ferrite-garnet films

We describe the experimental studies of both domain and crystal defect structure of magneto-optical bismuth-substituted ferrite-garnet films (FGF) with high Faraday effect. Indentation and scratching (sclerometric) tests of either magnetically uniaxial or easy plane anisotropy (“planar”) films were carried out in parallel with traditional chemical etching. We demonstrate the effect of strong local changes of magnetic anisotropy on the domain structure due to local mechanical stresses. New types of biperiodic domain structure imposed by external stresses were found to exist.

Spin Hall effect of light in a prism-waveguide coupling structure with a magneto-optical bimetallic film

We study the spin hall effect of light (SHEL) in prism coupling configuration with magneto-optical (MO) material and bimetallic film which is called MOSHEL. Compared with single gold film, the surface plasmon resonance (SPR) with the bimetallic film can achieve minimum reflectivity and the difference between transverse shifts with opposite magnetic field directions can achieve 13 μm at resonance angle. By adjusting the thickness of magneto-optical layer and bimetallic film, we find that both SPR and SHEL can be modulated by the magnetic field. Base on this we propose that MOSHEL can be enhanced by MOSPR for the first time.

Correlating non-linear behavior of in-plane magnetic field and local domain wall velocities for quantitative stress evaluation

There is a need in industry to supply safe, effective and reliable technique to characterize the stress of steel components and structures, both at the manufacturing stage and in service. Bridging the correlation between micro and macro magnetic properties and the applied tensile stress is the first conceptual step to come up with a new method of non-destructive material testing. We investigate the stress-associated changes in domain wall dynamics in grain-oriented electrical steel by in-situ magnetic imaging using magneto-optical indicator films. The 180° domain walls velocity distribution is used as a parameter for applied stress determination. Additionally, the in-plane magnetic stray field above the surface of the sample is synchronously measured for stress evaluation. The variations in magnetic stray field outside the sample under different loading are investigated for the analysis of the domain wall dynamics. From this, an interrelation of the domain wall dynamics and magnetic stray fields with varied tensile stress is derived. The results provide substantial microscopic and macroscopic insight for the interplay of domain wall dynamics and stress-induced demagnetizing effect.

Domain Structure and Magnetization Reversal Micromechanisms in Quasi-Two-Dimensional Exchange-Biased Nanomagnetics

Abstract—The domain structure and magnetization reversal mechanisms are studied in quasi-two-dimensional exchange-biased NiFe/FeMn and NiFe/NiO nanomagnetics, using a complex method of magnetooptical indicator films and acoustic emission. The presence of the axial dispersion of unidirectional anisotropy in grains of the antiferromagnetic layer is shown to determine the statistic distribution and chirality of spin springs near the interface. The acoustic emission signals caused by the excitation of elastic Lamb waves upon the magnetization reversal of NiFe/NiO heterostructure are found. The coercive force of these systems is due to irreversible processes to overcome potential barriers that are induced by the formation of spin springs with different chirality, localized in the antiferromagnetic near the ferromagnetic–antiferromagnetic boundary.

Power frequency domain imaging on Goss-textured electrical steel

Abstract A magneto-optical indicator film with perpendicular anisotropy (PMOIF) is used for time-resolved domain imaging on grain-oriented transformer steel at technical frequency field excitation. The high sensitivity of the PMOIF allows for single-shot imaging, even in the presence of insulation coatings. Differences between quasistatic and dynamic processes are elaborated, revealing the mechanisms of domain refinement and showing the role of grain boundaries and mechanical stress on domain formation and flux propagation. It is shown that the PMOIF technique opens a promising window for studying the domain dynamics of transformer steels under practical conditions, which goes beyond established characterization tools like Kerr microscopy.

Efficiency of Magnetooptical Conversion of Magnetic Fluxes Produced by the High-Temperature Superconductor Matrix

The possibility for using the ferrite-garnet magnetooptical films with a band domain structure has been considered with the aim of visualization of the spatial distribution of a magnetic flux near sensitive elements of a high-temperature superconductor matrix. The methods that enhance the efficiency of magnetooptical conversion have been suggested.

Monolithic magneto-optical oxide thin films for on-chip optical isolation

Abstract

Highly sensitive sensors of fluid detection based on magneto-optical optical Tamm state

We propose a new magneto-optical optical Tamm state (MOOTS) sensor in fluid detection. The device consists of a dielectric magneto-optical thin film of Ce-doped Y3Fe5O12 (CeYIG), a metallic film of Ag and a periods of the distributed Bragg reflector (DBR). Finite element method (FEM) and 4 × 4 transfer matrix method are employed to calculate the figure of merit (FOM) of sensitivity. Calculation results indicate that a FOM of 1224.21/RIU for gas refractive index variation from 1.0000 to 1.0006 can be obtained when the incident wavelength is 1064 nm, which is much larger than the FOM of magneto-optical surface plasmon resonance (MOSPR) device. Meanwhile, our MOOTS sensor is insusceptible to the influence of smoothness of the interface of deposited layers and can provide the great error tolerance, which is more conducive to the manufacture, production and actual performance. In addition, the experiment route to detect the refractive index of air and NaCl solution has been revealed.

Influence of Substrate Stage Temperature and Rotation Rate on the Magneto-Optical Quality of RF-Sputtered Bi2.1Dy0.9Fe3.9Ga1.1O12 Garnet Thin Films

Highly bismuth-substituted iron garnet thin films are prepared on quartz substrates by using a radio frequency (RF) magnetron sputtering technique. We study the factors (process parameters associated with the RF magnetron sputter deposition technique) affecting the magneto-optical (MO) properties of ferrite garnet films of composition Bi2.1Dy0.9Fe3.9Ga1.1O12. All films show high MO response across the visible range of wavelengths after being annealed. In particular, the effects of substrate stage temperature and rotation rate on the various properties of films are studied. Experimental results reveal that the characteristics of garnet films of this type can be tuned and optimized for use in various magnetic field-driven nanophotonics and integrated optics devices, and that, at a substrate stage rotation rate near 16 revolutions per minute, the MO quality of the developed MO films is the best, in comparison with films deposited at other rotation rates. To the best of our knowledge, this is the first report on the effects of deposition parameters on the properties of garnet films of this stoichiometry.

Доменная структура и микромеханизмы перемагничивания в квазидвумерных обменно-смещeнных наномагнетиках

Abstract —The domain structure and magnetization reversal mechanisms are studied in quasi-two-dimensional exchange-biased NiFe/FeMn and NiFe/NiO nanomagnetics, using a complex method of magnetooptical indicator films and acoustic emission. The presence of the axial dispersion of unidirectional anisotropy in grains of the antiferromagnetic layer is shown to determine the statistic distribution and chirality of spin springs near the interface. The acoustic emission signals caused by the excitation of elastic Lamb waves upon the magnetization reversal of NiFe/NiO heterostructure are found. The coercive force of these systems is due to irreversible processes to overcome potential barriers that are induced by the formation of spin springs with different chirality, localized in the antiferromagnetic near the ferromagnetic–antiferromagnetic boundary.

The change of domain structure of the amorphous microwire of Fe73.5Cu1Nb3Si13.5B9 composition under thermal treatment

The investigation on domain structure evolution under variation of magnetostriction, phase composition and internal stresses was provided. Glass-coated amorphous microwires of Fe73.5Cu1Nb3Si13.5B9 composition with positive magnetostriction were studied. The decrease of internal stresses and controlled crystallization leading to changes in the phase composition and reduction of magnetostriction were observed under different thermal treatment. The domain structure of the as-prepared and annealed microwires was studied by the method of magneto-optical indicator films. The estimation of the domain size was realized by Fourier transform from the domain contrast of magneto-optical images. The regularities of the influence of thermal treatment on the magnetic domain structure of microwires have been estimated.

A Linear Optical Current Transducer Based on Crystal Wedge Imaging Detection

This paper proposes a linear optical current transducer based on a crystal wedge imaging detection. It converts the Faraday magneto-optical rotation to the horizontal displacement of the light and dark interference fringes by using the crystal wedge, and then uses a dual-quadrant detector to locate the fringes to achieve a real-time measurement of current. Compared with the usual light intensity detection method it has the outstanding advantages of no optical power dependency, very low temperature drift, and simple algorithm and linear measurement. In addition, a magneto-optical film is employed to replace the magneto-optical crystal to cut down the optical path and the linear birefringence. The dual-quadrant detector is employed to achieve low cost, high resolution, and high precision. The experimental results show that the transducer meets the accuracy class 0.2 S.

A high-resolution combined scanning laser and widefield polarizing microscope for imaging at temperatures from 4 K to 300 K.

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as, for example, birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a 4He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via the Faraday effect, or imaging of structural features, such as twin-walls in tetragonal SrTiO3. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural, and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism, and superconductivity.

Using Kerr Microscopy for Direct Observation of Magnetic Domains in Ni–Mn–Ga Magnetic Shape Memory Alloy

Giant magnetic-field-induced strain up to 12% in Ni–Mn–Ga single crystal is due to magnetically-induced reorientation of the twinned martensitic low symmetry crystal structure. An important interplay is arising from the interaction between ferroelastic domains (twin domains) and magnetic domains. Here, we studied the magnetic domains in an Ni50Mn28Ga22 single crystal exhibiting 6% strain by using a magneto-optical indicator film and for the first time also directly by the Kerr magneto-optical microscopy. To compare the magnetization behavior of bulk and surface, we measured the magnetization loops by the Kerr effect (MOKE) and by the vibrating sample magnetometry. We demonstrate that using a particular arrangement of the Kerr microscopy enables visualizing the magnetic domains structure and its evolution in the magnetic field.