Layered structure of epitaxial yttrium iron garnet films

The layered structure of yttrium iron garnet films, ranging in thickness from 0.7 to 4.1 μm, grown epitaxially on single-crystal gallium-gadolinium garnet substrates, was investigated by x-ray spectral microanalysis. The ferrite films were chemically etched layer by layer in a mixture of orthophosphoric and sulfuric acids at T=353–423 K. It was established that the chemical composition of the films varies over the thickness because of the nonuniform distribution of gadolinium, gallium, lead, and platinum ions; the film-substrate transitional layer and the surface layer of the film differ most greatly with respect to the composition and magnetic properties. It was shown that the thickness of the transitional layers and their negative effect on the magnetic characteristics of ferrite films decrease appreciably if at the time of immersion of the substrate and pulling of epitaxial structure out of the fluxed solution the substrate holder together with a special mixer rotate at a rate of 50 rpm and the pulling velocity is 20 cm/min. Zh. Tekh. Fiz. 69, 62–64 (December 1999)     

Exchange coupling in ultrathin epitaxial yttrium iron garnet films

Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y₃Fe₅O₁₂ or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y₃Al₅O₁₂ or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied from 180 ? to 4600 ?. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis loops recorded for ultrathin YIG films have a “bee-waist” shape and show a coupling between two different magnetic phases. The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to be Y₃Fe_5-xAl_xO₁₂ due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures. This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling, the maximal interaction energy is estimated to be about 0.17 erg/cm² at 5 K for (111) oriented sample. Received 3 June 2002 / Received in final form 7 October 2002 Published online 27 January 2003 RID="a" ID="a"Presently at LPM, Université H. Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy e-mail: popova@lpm.u-nancy.fr     

Thermal stability of the magnetic parameters of epitaxial iron garnet films subjected to planar radial stresses

The effect of external planar radial pressure on the thermal stability of the magnetic parameters of epitaxial iron garnet films is investigated in the temperature range 200–500 K for external mechanical stresses in the range 0–40 kgf/mm². It is shown that external planar radial pressure can be used to improve the thermal stability of these magnetic parameters by a factor of 1.5–2, and also to alter significantly the temperature interval of single-domain behavior for orientational phase transitions near a compensation point. Zh. Tekh. Fiz. 67, 114–116 (September 1997)     

Low-temperature ferromagnetic resonance in epitaxial garnet films on paramagnetic substrates

The temperature dependence (4.2–300 K) of ferromagnetic resonance (FMR) in the 3-cm range in films of yttrium-iron garnet (YIG)1.7–3 m thick, epitaxially grown on a paramagnetic gadolinium-gallium garnet (GGG) paramagnetic substrate is studied. It is found that with decrease in temperature, beginning at T 70 K, the temperature dependences of the resonant FMR fields _res and _res for magnetic fields applied parallel and perpendicular to the normal to the film deviate from similar dependences for a free thin YIG plate, which approach the value of / for YIG. This deviation increases approximately in proportion to T^–1, reaching hundreds of Oe at T=4.2 K. It is established that the given effect is related to the additional static magnetic field H_p created in the YIG film by the paramagnetic substrate, and is dependent on the form of the latter.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–53, April, 1989.     

Study of the branching domain structures in epitaxial films of yttrium iron garnet by end face magnetic force microscopy

The distribution of the magnetization vector on the free surface and end (cleaved facet) of thick epitaxial yttrium iron garnet films has been studied by the scanning magnetic-force microscopy method. Volume fractal-like branching of the domain structure has been found at the interface of the film and the free space with the refinement of the formed partial branches of the stripe (labyrinth) domains. Triangular closing domains have been observed at the interface between the film and the substrate. Direct experimental proof of the existence of the static horizontal Bloch lines within the stripe domain walls has been obtained.     

Possible identification of magnetostatic surface spin wave modes in ferromagnetic resonance on epitaxial yttrium—iron—garnet films

In ferromagnetic resonance experiments of yttrium—iron—garnet films, resonances have been observed whose characteristics are consistent with their interpretation as magnetostatic surface spin wave modes.     

Wavelength modulation spectroscopy based on quasi-continuous-wave diode lasers

A modified wavelength modulation spectroscopy（WMS）based on the self-heating effect of the tunable diode laser when driven in quasi-continuous-wave（QCW）mode is investigated.A near-infrared distributed feedback（DFB）diode laser working at the QCW mode is employed as the QCW light source,and CO2 is selected as the target gas.The characteristic of the QCW second harmonic（2f）line profile is analyzed through a comparison with that of the traditional CW WMS with the same system.A noise-equivalent absorbance of 3.2×10-5 Hz-1/2 for CO2 at 1.58μm is obtained with 18-m optical path.The QCW WMS lowers the dependence on lasers and expands selectivity,thus verifying the feasibility of the method.     

Optical isolators using Bi-substituted rare-earth iron garnet films

Using Bi-substituted rare-earth iron garnet film, (GdBi)₃ (FeAlGa)₅O₁₂ or (YbTbBi)₃ Fe₅O₁₂, grown by liquid phase epitaxy technique, we have fabricated a compact, low cost and high performance optical isolator for near-infrared wavelength region, in comparison with conventional isolator using yttrium iron garnet (YIG) single crystal as Faraday rotator. Typical insertion loss and isolation of developed isolators are 0.6 dB and 35 dB respectively at =1.31 m and the size is 6×6 mm. The isolators, which could be used in the wavelength range of 1.31 to 1.55 m, are also fabricated with insertion loss of less than 1.1 dB and isolation of more than 35 dB.     

Luminescence of gadolinium gallium garnet epitaxial films under excitation by synchrotron radiation

The luminescence excited by synchrotron radiation in gadolinium gallium garnet single-crystal films grown by liquid-phase epitaxy from lead-and bismuth-containing solution melts on Gd₃Ga₅O₁₂ substrates is investigated. It is shown that the luminescence intensity in the visible range of the spectrum depends on the type and concentration of impurity ions passing from the solvent into the film.     

Reversible-adsorption-induced variation of domain width in iron garnet films

It has been found using the Faraday-effect magneto-optic method that the width of magnetic domains of the labyrinth domain structure in bismuth-containing iron garnet films with perpendicular anisotropy changes considerably after the adsorption of methanol molecules. A maximum change in domain width of 50% has been observed in methanol saturated vapor. This effect is reversible. A decrease in domain width under adsorption has been attributed to a decrease in the effective constant of the perpendicular magnetic anisotropy of the film caused by the adsorption of methanol molecules.     

Structure and properties of deposited yttrium iron garnet films

Ferromagnetic resonance (FMR) and vibrating-sample magnetometer techniques were used to study the nature of the structural characteristics of yttrium iron garnet films deposited through either liquid phase epitaxy or laser evaporation on a (111)-oriented gallium gadolinium garnet substrate. It was proved that, based on the experimentally observed cubic magnetic anisotropy, deposited films should be considered to be single crystals. However, the absence of the FMR domain branch in a nonsaturated film and the shape of the magnetization curve indicate that a deposited film when demagnetized does not have a domain structure, as would be expected for a single-crystal film. According to the model proposed, a deposited film consists of close-packed single-crystal fragments with equal crystallographic orientation, the boundaries between which are in a partially atomically disordered state. As a result, such a film is both locally and macroscopically anisotropic, like a continuous single crystal. This film can split into domains only within a fragment (as is the case in a magnetic granular polycrystal); however, this does not happen, because the linear dimensions of a submicroscopic fragment are smaller than the equilibrium domain width.     

Bias-field-induced spiral dynamic domains induced in iron garnet films

The induction of an Anger state (AS) in a multidomain magnetic medium by a static bias magnetic field is observed. The properties of the spiral dynamic domains in the induced AS are substantially different from those of previously studied spiral domains. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 60–64 (10 January 1997)     

Spectral and luminescence properties of gadolinium gallium garnet epitaxial films doped with terbium

Gadolinium gallium garnet single-crystal films containing terbium are grown through liquid-phase epitaxy from a supercooled solution melt in the PbO-B₂O₃ system. The optical absorption spectra in the wavelength range 0.2–10.0 μm and the luminescence spectra excited by synchrotron radiation with energies in the range 3.5–30.0 eV are investigated at temperatures of 10 and 300 K. It is revealed that the optical absorption spectra contain an absorption band with the maximum at a wavelength λ ≈0.260 μm, which corresponds to the spin-allowed electric dipole transition between the electronic configurations 4f ⁸(⁷ F ₆) → 4f ⁷(⁸ S)5d of the Tb³⁺ ions. The narrow low-intensity absorption bands attributed to the 4f → 4f transitions from the ⁷ F ₆ ground level to the ⁷ F _0–5 multiplet levels of the Tb³⁺ ions are observed in the wavelength range 1.7–10.0 μm. In the luminescence spectra measured at a temperature of 10 K, the highest intensity is observed for a band with the maximum at a wavelength λ ≈ 0.544 μm, which is associated with the ⁵ D ₄ → ⁷ F ₅ radiative transition in the Tb³⁺ ion.     

Wideband magneto-optic modulation in a bismuth-substituted yttrium iron garnet waveguide

We present a tunable wideband bismuth-substituted yttrium iron garnet (Bi-YIG) waveguide magneto-optic (MO) modulator. High-speed current transients are used to switch the in-plane magnetization of the film, which modulates an 800 nm optical beam. Large bandwidth optical modulation is achieved by driving the device in a non-resonant mode that is well below the ferromagnetic resonance frequency of the film. The MO modulator has the potential of operating at bandwidths higher than 1 GHz by tuning the applied static magnetic field.     

A manifestation of magnetism of bismuth in iron garnet films

Bismuth iron garnet films prepared through electron-beam and laser-induced evaporation on (001)-oriented substrates of scandium gallium gadolinium garnet are investigated using ferromagnetic resonance. It is assumed that the additional minima observed in the angular dependence of the resonance field can be associated with the magnetic moment of bismuth ions.     

Low relaxation rate in epitaxial vanadium-doped ultrathin iron films

The longest relaxation time and sharpest frequency content in ferromagnetic precession is determined by the intrinsic (Gilbert) relaxation rate G. For many years, pure iron (Fe) has had the lowest known value of G = 57 MHz for all pure ferromagnetic metals or binary alloys. We show that an epitaxial iron alloy with vanadium (V) possesses values of G which are significantly reduced to 35 +/- 5 MHz at 27% V. The result can be understood as the role of spin-orbit coupling in generating relaxation, reduced through the atomic number Z.     

Optical harmonic generation in magnetic garnet epitaxial films near the fundamental absorption edge

Spectra of the second and third optical harmonics generated in epitaxial films of magnetic garnets were studied in the ranges 1.7–3.2 and 2.4–4.2 eV, respectively. A large magnetic contrast was revealed in second-optical-harmonic spectra, which reaches 100% at certain photon energies. By contrast, the symmetry-allowed magnetic contribution to spectra of the third optical harmonic was not found. While linear absorption in ferrite-garnet films grows by two orders of magnitude above the fundamental absorption edge at ～3.2 eV, the intensity of nonlinear spectra did not reveal any noticeable increase over this spectral range.     

Measurement of the refractive index and optical absorption spectra of epitaxial bismuth substituted yttrium iron garnet films at uv to near-ir wavelengths

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y_3–x–y Bi _x Pb _y Fe_5–z Pt _z O₁₂ films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.     

Wavelength modulation diode laser absorption spectroscopy for high-pressure gas sensing

A general model for 1f-normalized wavelength modulation absorption spectroscopy with nf detection (i.e., WMS-nf) is presented that considers the performance of injection-current-tuned diode lasers and the reflective interference produced by other optical components on the line-of-sight (LOS) transmission intensity. This model explores the optimization of sensitive detection of optical absorption by species with structured spectra at elevated pressures. Predictions have been validated by comparison with measurements of the 1f-normalized WMS-nf (for n = 2–6) lineshape of the R(11) transition in the 1st overtone band of CO near 2.3 μm at four different pressures ranging from 5 to 20 atm, all at room temperature. The CO mole fractions measured by 1f-normalized WMS-2f, 3f, and 4f techniques agree with calibrated mixtures within 2.0 %. At conditions where absorption features are significantly broadened and large modulation depths are required, uncertainties in the WMS background signals due to reflective interference in the optical path can produce significant error in gas mole fraction measurements by 1f-normalized WMS-2f. However, such potential errors can be greatly reduced by using the higher harmonics, i.e., 1f-normalized WMS-nf with n > 2. In addition, less interference from pressure-broadened neighboring transitions has been observed for WMS with higher harmonics than for WMS-2f.