To measure the Raman scattering spectrum of a monolayer graphene sample, we describe the design and development of a high-efficiency optical measurement device for operation within the small bore of a high-power magnet at low temperature. For the high-efficiency measurement of light emitted from this small region, we designed a compact confocal optics with lens focusing and tilting systems, and used a piezodriven translation stage that allows micron-scale focus control of the sample position. In addition, we show a detailed technique of adjustment of optical axes, and explain the importance of the focusing and tilting systems. The operation of the device was confirmed by Raman scattering measurements of monolayer graphene on quartz glass with a high signal-to-noise ratio. Though the light collection efficiency of the device is about 240-fold smaller than that of a conventional optical microscope, the device has a sufficient collection efficiency for detecting the Raman scattering light of monolayer graphene.

We have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200 oC); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/µm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.

Iron oxide nanoparticles (NPs) have attracted a lot of interest due to their many potential applications in areas including optoelectronics, magneto-optics, high density data storage, etc. In particular, iron oxides (Fe3O4 and γ –Fe2O3) are also well suited for biomedical applications [1]. We have investigated Faraday Rotation (FR) response for two types of Fe2O3 NPs (in aqueous suspension) that are of the same average diameter (10 nm) but differ in one important respect; one group consists of uncoated particles whereas the other group is functionalized with caffeic acid. This system is being investigated and characterized for use in tumor imaging applications. Faraday rotation (FR) refers to the rotation of the polarization vector of a light beam as it passes through a sample in the presence of a magnetic field. FR can reveal interesting material properties such as saturation magnetization and wavelength dependent Verdet constant of the material under investigation. The latter is a measure of the magnetically induced birefringence of the material. Typically FR setups rely on AC or DC magnetic fields. While these are valuable techniques with their own advantages, this work focuses on a pulsed field setup that can reveal dynamic information about the resulting magnetization, as the magnetic response of the sample is measured in the presence of short intense fields on the order of 0.6 Tesla and lasting approximately 100 milliseconds. All experiments are carried out at excitation wavelength of 633 nm (He-Ne wavelength).

The two NP samples show very different response to the field pulses. The NP systems investigated in this work show very unique short term and long term behavior revealing various time scales of interest. These unique characteristic times for the functionalized vs. uncoated particles provide valuable clues about the magnetization response of the NP and its relationship to the detailed structure of the NPs (core vs. shell). Magnetic response from these systems persists long after the magnetic field pulse has subsided. This can be related to the relaxation modes (Néel vs. Brownian) and as possible evidence of NP size dispersion. Additionally, the possibility of agglomeration is also discussed. While more detailed quantitative analysis will be dealt with in a more comprehensive publication that is under preparation, we hope to show in this preliminary report both that the AC and pulsed FR measurements can reveal complimentary information and that FR in general can be a reliable technique, which can be used to develop a detailed picture of the magnetic response of these NP systems.

We report on mid-infrared (600 – 4000 cm-1), refection-type optical-Hall effect measurements on epitaxial graphene grown on C-face silicon carbide and present Landau-level transition features detected at 1.5 K as a function of magnetic field up to 8 Tesla. The Landau-level transitions are detected in reflection configuration at oblique incidence for wavenumbers below, across and above the silicon carbide reststrahlen range. Small Landau-level transition features are enhanced across the silicon carbide reststrahlen range due to surface-guided wave coupling with the electronic Landau-level transitions in the graphene layer. We analyze the spectral and magnetic-field dependencies of the coupled resonances, and compare our findings with previously reported Landau-level transitions measured in transmission configuration [4,5,6]. Additional features resemble transitions previously assigned to bilayer inclusion [21], as well as graphite [15]. We discuss a model description to account for the electromagnetic polarizability of the graphene layers, and which is sufficient for quantitative model calculation of the optical-Hall effect data.

Vector magneto-optical generalized ellipsometry on passivated ferromagnetic permalloy slanted columnar thin films is reported. The nanostructured thin film was grown by electron-beam glancing angle deposition and subsequently coated with a thin Al2O3 layer by atomic layer deposition. Magneto-optical generalized ellipsometry data have been acquired while an external magnetic field H with constant amplitude was rotated with respect to the sample (spatial hysteresis loops). The magneto-optical coupling parameters, which are proportional to the sample magnetization M, reveal intriguing anisotropic magnetic behavior of the slanted columnar thin film. Three-dimensional graphs of the magneto-optical coupling parameters with respect to spatial hysteresis loops shown here are representative for the sample magnetization.

An optical isolator with a TiO2/(CeY)3Fe5O12 guiding layer was studied. A nonreciprocal phase shift was calculated in the magneto-optic waveguide with the TiO2/(CeY)3Fe5O12 guiding layer at a wavelength of 1.55 μm. By employing a multimode interference coupler as coupling devices, the total device length of approximately 600 μm was achieved. An interferometric optical isolator with distinct layer structures, which could be operated in a unidirectional magnetic field, was also designed.

Photonic integration has proved remarkably successful in combining multiple optical devices onto a single chip with the benefits of added functionality, and reduction in costs, arising from the replacement of manual assembly and alignment of individual components with lithographic techniques. However, the incorporation of optical isolators and related non-reciprocal devices within standard optoelectronic wafer platforms is exceptionally challenging. Preferred magneto-optic materials cannot be exploited as waveguide core layers on semiconductor wafers due to a lower refractive index. Another difficulty is the phase velocity mismatch as a consequence of the inherent structural birefringence associated with waveguide geometries.

Our approach to the integration of an optical isolator with a III-V semiconductor laser involves combining a nonreciprocal mode converter with a reciprocal mode converter, based on an asymmetric profiled rib waveguide, fabricated by Reactive Ion Etching. We demonstrate that suitably tapered waveguides can be employed to connect the mode converter to other sections thereby avoiding problems caused by mode-matching and reflections from the section interfaces.

The nonreciprocal mode converter is formed from a continuation of the III-V semiconductor waveguide core with a magneto-optic upper cladding so that Faraday rotation occurs through the interaction of the evanescent tail. The phase velocity mismatch due to the waveguide birefringence is overcome using a quasi-phase-matching approach. Lithography is used to pattern the top cladding so that the film immediately on top of the waveguide core alternates between magnetooptic and a non-magneto-optic dielectric of a similar refractive index. Our first demonstrations used a dielectric (silica or silicon nitride) patterned by etching, or lift-off, on top of a GaAs rib waveguide, over which was deposited a magneto-optic film. This film was deposited by sputtering from a Ce:YIG target and demonstrated magnetic hysteresis, but, as it was not annealed, it was believed to consist of Ce:YIG and/or gamma iron oxide microcrystallites embedded in an amorphous matrix. With quasi-phase-matching periods of 110–160 μm and a waveguide length of 8 mm, we were able to demonstrate up to 12% non-reciprocal TE- to TM-mode conversion around a wavelength of 1.3 μm using the remanent magnetisation.

In order to enhance the magneto-optic effect it is desirable to anneal such films. However the mismatch in thermal expansion coefficients results in a catastrophic failure of samples with large area film coverage. This problem has been shown to be alleviated by patterning the YIG film. Unfortunately wet-etching of YIG also etches (Al)GaAs and, therefore, the development of a lift-off process for YIG deposition has been undertaken. Initial results are promising with ∼100 μm×2.5 μm YIG sections deposited on a GaAs layer which remain intact after an anneal in an oxygen atmosphere.

We report site-selective studies of the Zeeman splittings that are observed for magnetic fields up to 6.6T for different Eu incorporation sites in GaN. Utilizing resonant excitation with visible light, we are able to distinguish the site and find for one center (Eu1) a splitting into five components as expected for C3v symmetry. The corresponding g-values are 1.66 and 1.90. The two lines of another center Eu2 each split into two levels corresponding to g-values of 1.9 and 2.84. Most surprisingly a third center, for which only one line is clearly identified, a g-value of 6.16 is found which is larger than can be explained for a 7F2 purely ionic Eu state.

Garnet films based on (BiPrGdLu) (FeGa) have been grown on (210) and (100) oriented SGGG substrates. (210) films with an easy plane of magnetization provided optimal imaging contrast. Incorporation of Au nanoparticles into an epitaxially grown film was done and these films show an increase in Faraday rotation, ostensibly due to the plasmon resonance effect.

Structural and magneto-optical properties of Ni-doped amorphous AlN layers (a-AlN) deposited by radio frequency (rf) sputtering on Silicon (001) substrates were investigated. The as-grown material exhibits weak ferromagnetic behavior as evidenced by the magneto-optic Kerr effect (MOKE) measurement with Kerr rotation less than 100 μrad at room temperature regardless of the Ni fraction. The samples with a Ni concentration below 10 at.% show a weak but monotonically increasing MOKE signal with post-growth annealing temperature. A hundred-fold increase in the Kerr rotation value was observed for samples with Ni content exceeding 20 at.% after thermal annealing at 450°C in nitrogen; and the Kerr rotation value abruptly decreases above that temperature. The morphology of as-grown and annealed a-AlN:Ni films were characterized by small angle x-ray scattering and transmission electron microscopy. It was found that the as-deposited film contains nano-particles of different sizes with average diameters less than 30 nm. The size distribution of nano-particles in the thermally annealed a-AlN:Ni was studied as a function of annealing time and temperature. The results correlate well with those obtained from the MOKE measurements.

Surface activated direct bonding of a magnetooptic garnet crystal to a Silicon-On-Insulator (SOI) wafer is discussed for the application to waveguide optical nonreciprocal devices. An interferometric waveguide isolator is discussed that uses nonreciprocal phase shift brought about by a first-order magneto-optic effect. In an SOI waveguide, the low refractive index of buried oxide layer enhances the magneto-optic phase shift. This contributes to reduce the device size together with the strong field confinement of high index contrast waveguide. The interferometric isolator can be extended to an optical circulator by adopting appropriate 3-dB directional couplers to construct a Mach-Zehnder interferometer.

Magneto-optical garnet based optical circulator was designed and fabricated with wafer-scale technology. Modeling and simulation strategy is established for the optimization of a new design of circulator based on ring cavity. Wafer-scale technological process is developed and demonstrated allowing fabrication of the optimized BIG/GGG buried ring circulator.

We show that nonreciprocal Bloch-like oscillations can emerge in passive optical waveguide arrays with linearly growing effective index in the absence of loss or gain. Spectral asymmetry, a difference in propagation constants and Bloch oscillation periods in opposite propagation directions, are established by imposing different vertical spatial index gradients at the substrate/core, and core/cover interfaces in the presence of transverse magnetization. A model system consisting of an array of transversely magnetized asymmetric garnet/silicon-on-insulator waveguides is presented.

The optical isolator made of diluted magnetic semiconductor and the isolator made of a ferromagnetic-metal/semiconductor hybrid have been developed aiming to integrate nonreciprocal optical devices, such as an optical isolator and optical circulator, into the semiconductor-made optoelectronic integrated circuits,. The Cd1-xMnxTe exhibits a huge Faraday effect and can be grown on a semiconductor substrate. For Cd1-xMnxTe waveguide with a Cd1-xZnxTe/ Cd1-xMnxTe quantum well grown on GaAs substrate we achieved a high Faraday rotation of 2000 deg/cm, a high isolation ratio of 27 dB, a low optical loss of 0.5 dB/cm, and a high magneto-optical figure-of-merit of 2000 deg/dB/kG in a wide 25-nm wavelength range. It was predicted theoretically and proved experimentally the effect of non-reciprocal loss in hybrid semiconductor/ferromagnetic metal waveguides. This effect can be use for new design of waveguide optical isolator. Because of its simplicity and technological compatibility, this design is attractive for the integration into optoelectronic integrated circuits. The magneto-optical figure-of merit of 7% was demonstrated for the AlGaAs passive optical waveguide covered by Co.

Magneto-optical properties of Ni- and Co-doped amorphous AlN thin films were investigated as a function of post grown annealing temperature using magneto-optical Kerr effect (MOKE) spectroscopy. The x-ray diffraction spectra confirmed that the as-grown material is amorphous and retained its morphology after thermal treatment; however the sample morphology strongly depends on the concentration of incorporated transition metals. We observed with help of transmission electron microscopy and atomic force microscopy that the films surface containing TMs with concentrations larger than ∼10 at.% undergo morphological changes suggesting possible Ni and Co atom clustering. Significant enhancement of the polar Kerr rotation signal was observed for Ni- and Co-doped a-AlN materials annealed above 300 °C in nitrogen. The studied materials have shown strong magnetic isotropy in polar geometry whereas the MOKE measurements in longitudinal geometry did not show an explicit signal for the transition metals doped a-AlN studied.

Despite research efforts to find a better nano-optical transducer for light localization and high transmission efficiency for existing and emerging plasmonic applications, there has not been much consideration on improving the near-field optical performance of the system by engineering the near-field sample. In this work, we demonstrate the impact of tailoring the near-field sample by studying an emerging plasmonic application, namely heat-assisted magnetic recording. Basic principles of Maxwell's and heat transfer equations are utilized to obtain a magnetic medium with superior optical and thermal performance compared to a conventional magnetic medium.

We have developed an experimental set-up based on time-resolved Magneto-Optical Kerr Effect (MOKE) that allows to retrieve the vectorial magnetization dynamics in thin films with sub-picosecond resolution. This method has been exploited to measure the variations of the magnetization (modulus and orientation) induced by an ultrashort laser pulse. The initial demagnetization is established at the electronic level within a few hundreds of femtoseconds through electron-magnon excitations. The subsequent dynamics is characterized by a precessional motion on the 100 picosecond time-scale, around an effective, time-dependent field. Following the full dynamics of the magnetization, we have unambiguously determined the temporal evolution of the magneto-crystalline anisotropy, providing the clear experimental evidence that the precession is triggered by the rapid, optically-induced misalignment between the magnetization vector and the effective field. This method provides a simple and widely applicable way to study both magnetization and anisotropy in the sub-picosecond regime and therefore to unravel the mechanisms underlying the ultrafast evolution of the spin order in magnetic media.

Two fundamentally different types of domains were resolved in multiferroic MnWO4 by optical second harmonic generation (SHG). Hybrid-multiferroic (absolute) domains reflect the magnetic chirality coupled 1:1 to the spontaneous polarization because of the magnetic origin of the ferroelectric order. Magnetic translation (relative) domains reflect discontinuities in the progression of the magnetic spin spiral. SHG topography is the only experimental method so far allowing one to image both types of domains. The imaging procedure and the SHG contributions involved are therefore discussed in detail.

We present a time-resolved magneto-optical (MO) imaging study of high-temperature superconductor (HTS) in high-frequency alternating current (AC) regime. The evolution of the magnetic flux density distribution in YBa2Cu3O7-d (YBCO) thin film samples is studied in small steps of the phase of the applied AC current. The flux distribution at 10 K exhibits instabilities including flux jumps and flux creep. A quantitative analysis of the data allows us to obtain the current density evolution. The current profile changes considerably with the phase differently from the prediction of the critical state model. These observations can be explained by the higher self-field at the sample edge and the effects of flux creep.

A large nonlinear magneto-optical effect is observed in a non-centrosymmetric Fe/AlGaAs (001) heterostructure. This effect is a direct consequence of interference between second-harmonic optical waves of magnetic and crystallographic origin, generated at ferromagnetic Fe interface and bulk AlGaAs, respectively. The longitudinal nonlinear Kerr rotation is measured to be 1.6° along the [1-10] hard axis, about two orders of magnitude stronger than the linear equivalent. The rotational second-harmonic signal shows large magnetic contrast along all the in-plane directions, demonstrating a high sensitivity to the magnetization of an anisotropic interface in the longitudinal geometry.