Optical and magneto-optical behavior of Cerium Yttrium Iron Garnet thin films at wavelengths of 200-1770 nm.

Magneto-optical cerium-substituted yttrium iron garnet (Ce:YIG) thin films display Faraday and Kerr rotation (rotation of light polarisation upon transmission and reflection, respectively) as well as a nonreciprocal phase shift due to their non-zero off-diagonal permittivity tensor elements, and also possess low optical absorption in the near-infrared. These properties make Ce:YIG useful in providing nonreciprocal light propagation in integrated photonic circuits, which is essential for accomplishing energy-efficient photonic computation and data transport architectures. In this study, 80 nm-thick Ce:YIG films were grown on Gadolinium Gallium Garnet substrates with (100), (110) and (111) orientations using pulsed laser deposition. The films had bulk-like structural and magnetic quality. Faraday and Kerr spectroscopies along with spectroscopic ellipsometry were used to deduce the complete permittivity tensor of the films in the ultraviolet, visible and near-infrared spectral region, and the magneto-optical figure of merit as a function of wavelength was determined. The samples showed the highest IR Faraday rotation reported for thin films of Ce:YIG, which indicates the importance of this material in development of nonreciprocal photonic devices.

Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO3 films.

Cobalt-substituted SrTiO3 films (SrTi0.70Co0.30O(3-δ)) were grown on SrTiO3 substrates using pulsed laser deposition under oxygen pressures ranging from 1 µTorr to 20 mTorr. The effect of oxygen pressure on structural, magnetic, optical, and magneto-optical properties of the films was investigated. The film grown at 3 µTorr has the highest Faraday rotation (FR) and magnetic saturation moment (M(s)). Increasing oxygen pressure during growth reduced M(s), FR and optical absorption in the near-infrared. This trend is attributed to decreasing Co2+ ion concentration and oxygen vacancy concentration with higher oxygen partial pressure during growth.

Magnetostriction in epitaxial SrTi(1-x)Fe(x)O(3-δ) perovskite films with x = 0.13 and 0.35.

The crystal structure, magnetic anisotropy and magnetoelasticity of epitaxial SrTi(0.87)Fe(0.13)O(3-δ) (STF13) and SrTi(0.65)Fe(0.35)O(3-δ) (STF35) films grown on (001), (011), and (111) oriented SrTiO(3) substrates were investigated. The films grew with compressive in-plane strain and underwent tetragonal, monoclinic, and rhombohedral distortions on the (001), (011), and (111) substrates, respectively. All samples showed room temperature magnetic hysteresis loops with strong out-of-plane anisotropy. The resulting magnetoelastic anisotropy was an order of magnitude greater than the magnetocrystalline and shape anisotropies. Magnetoelastic coefficients of B(1) =- 6.7 × 10(6) and B(2) =- 28 to -26 × 10(6) erg cm(-3) for STF13 and B(1) =- 2.0 × 10(6) and B(2) =- 5.4 to -3.9 × 10(6) erg cm(-3) for STF35 were determined from the magnetic anisotropy and lattice strain, corresponding to magnetostriction constants of λ(100) = 2.09 × 10(-6) and λ(111) = 7.68 × 10(-6) for STF13, and λ(100) = 0.62 × 10(-6) and λ(111) = 1.07 × 10(-6) for STF35.

Magneto-Optical Thin Films for On-Chip Monolithic Integration of Non-Reciprocal Photonic Devices.

Achieving monolithic integration of nonreciprocal photonic devices on semiconductor substrates has been long sought by the photonics research society. One way to achieve this goal is to deposit high quality magneto-optical oxide thin films on a semiconductor substrate. In this paper, we review our recent research activity on magneto-optical oxide thin films toward the goal of monolithic integration of nonreciprocal photonic devices on silicon. We demonstrate high Faraday rotation at telecommunication wavelengths in several novel magnetooptical oxide thin films including Co substituted CeO2-δ, Co- or Fe-substituted SrTiO3-δ, as well as polycrystalline garnets on silicon. Figures of merit of 3~4 deg/dB and 21 deg/dB are achieved in epitaxial Sr(Ti0.2Ga0.4Fe0.4)O3-δ and polycrystalline (CeY2)Fe5O12 films, respectively. We also demonstrate an optical isolator on silicon, based on a racetrack resonator using polycrystalline (CeY2)Fe5O12/silicon strip-loaded waveguides. Our work demonstrates that physical vapor deposited magneto-optical oxide thin films on silicon can achieve high Faraday rotation, low optical loss and high magneto-optical figure of merit, therefore enabling novel high-performance non-reciprocal photonic devices monolithically integrated on semiconductor substrates.

Combinatorial pulsed laser deposition of Fe, Cr, Mn, and Ni-substituted SrTiO3 films on Si substrates.

Combinatorial pulsed laser deposition (CPLD) using two targets was used to produce a range of transition metal-substituted perovskite-structured Sr(Ti(1-x)M(x))O(3-δ) films on buffered silicon substrates, where M = Fe, Cr, Ni and Mn and x = 0.05-0.5. CPLD produced samples whose composition vs distance fitted a linear combination of the compositions of the two targets. Sr(Ti(1-x)Fe(x))O(3-δ) films produced from a pair of perovskite targets (SrTiO(3) and SrFeO(3) or SrTiO(3) and SrTi0(0.575)Fe(0.425)O(3)) had properties similar to those of films produced from single targets, showing a single phase microstructure, a saturation magnetization of 0.5 µ(B)/Fe, and a strong out-of-plane magnetoelastic anisotropy at room temperature. Films produced from an SrTiO(3) and a metal oxide target consisted of majority perovskite phases with additional metal oxide (or metal in the case of Ni) phases. Films made from SrTiO(3) and Fe(2)O(3) targets retained the high magnetic anisotropy of Sr(Ti(1-x)Fe(x))O(3-δ), but had a much higher saturation magnetization than single-target films, reaching for example an out-of-plane coercivity of >2 kOe and a saturation magnetization of 125 emu/cm(3) at 24%Fe. This was attributed to the presence of maghemite or magnetite exchange-coupled to the Sr(Ti(1-x)Fe(x))O(3-δ). Films of Sr(Ti(1-x)Cr(x))O(3-δ) and Sr(Ti(1-x)Mn(x))O(3-δ) showed no room temperature ferromagnetism, but Sr(Ti(1-x)Ni(x))O(3-δ) did show a high anisotropy and magnetization attributed mainly to the perovskite phase. Combinatorial synthesis is shown to be an efficient process for enabling evaluation of the properties of epitaxial substituted perovskite films as well as multiphase films which have potential for a wide range of electronic, magnetic, optical, and catalytic applications.

Self-assembled single-phase perovskite nanocomposite thin films.

Thin films of perovskite-structured oxides with general formula ABO(3) have great potential in electronic devices because of their unique properties, which include the high dielectric constant of titanates, (1) high-T(C) superconductivity in cuprates, (2) and colossal magnetoresistance in manganites. (3) These properties are intimately dependent on, and can therefore be tailored by, the microstructure, orientation, and strain state of the film. Here, we demonstrate the growth of cubic Sr(Ti,Fe)O(3) (STF) films with an unusual self-assembled nanocomposite microstructure consisting of (100) and (110)-oriented crystals, both of which grow epitaxially with respect to the Si substrate and which are therefore homoepitaxial with each other. These structures differ from previously reported self-assembled oxide nanocomposites, which consist either of two different materials (4-7) or of single-phase distorted-cubic materials that exhibit two or more variants. (8-12) Moreover, an epitaxial nanocomposite SrTiO(3) overlayer can be grown on the STF, extending the range of compositions over which this microstructure can be formed. This offers the potential for the implementation of self-organized optical/ferromagnetic or ferromagnetic/ferroelectric hybrid nanostructures integrated on technologically important Si substrates with applications in magnetooptical or spintronic devices.