CEMs and Faraday rotation study of γ-Fe2O3- Fe3O4films obtained by a new pyrolisis technique

Thin film iron oxides prepared by a new pyrolisis technique are studied by means of CEM spectroscopy and Faraday rotation measurements. It is shown that Fe3O4spinel oxides are obtained when the deposition is performed under Ar atmosphere. These spinel-ferrite films present an important magnetization component perpendicular to the film plane. It is also shown that the Fe3O4films are converted to γ-Fe2O3by oxidation in air while retaining a uniaxial magnetic anisotropy. We interpret this induced magnetic anisotropy as arising from a magnetoelastic coupling with the substrate. Faraday rotation hysteresis loops confirm the existence of a strong induced uniaxial magnetic anisotropy in these films.     

Uniaxial and cubic anisotropy constants in ion-implanted Sm,Tm,Ga:YIG bubble thin films

The effects of ion implantation into (SmTmY)3(GaFe)5O12garnet thin films have been studied by ferromagnetic resonance. He+ ions were used for implantation with doses ranging from 3 to 4 × 10¹⁵He+/ cm²and implantation energy ranging from 150 to 175 Kev. The uniaxial and cubic anisotropy constants have been studied as a function of temperature from 0°C to 100°C for both as-grown and ion-implanted films. The implantation has effectively changed an easy-axis anisotropy to that of an easy plane in the implanted layers of the films. A cubic anisotropy constant K1with values varying from 4 × 10³to 6 × 10³erg/cm³at room temperature has been observed in these films. The results also indicated that to the first order, the implanted region in the film was essentially magnetically uncoupled from the bulk of the film.     

Amorphous Gd-Fe alloy films prepared by RF cosputtering technique

Amorphous GdxFe1-x(0 < x < 0.35) thin films were prepared by RF cosputtering using an iron target covered partially with small gadolinium pieces. The composition dependences of saturation magnetization, hysteresis curves, and domain structures were studied. Spark-like domains were observed when the magnetization was reversed from saturation. The uniaxial anisotropy was induced perpendicular to the film plane. The average value of the perpendicular uniaxial anisotropy constant Ku was about 2 × 10⁵erg/cm³. Ku, however, decreases as the saturation moment decreases in the vicinity of room temperature compensation. The stripe domain width was varied from 0.3 to 4 microns as the saturation moment decreased from 300 to 20 gauss. These magnetic properties of amorphous Gd-Fe sputtered films are similar to those of amorphous Gd-Co films.     

Thermomagnetic writing in homogeneous MnBi films

The specific Faraday rotation of the homogeneous low-temperature phase (LTP) and quenched high-temperature phase (HTP) MnBi films used for the writing experiments was measured to be9.5times10^{5}degrees per centimeter and4.3times10^{5}degrees per centimeter, respectively, at 25°C and a light wavelength of 632.8 nm. The coercive field of the films decreased exponentially with increasing film thickness for both phases. Thermomagnetic writing experiments showed that the written spots (1 to 10 μm in diameter) were not satisfactorily stable for films thicker than 50 nm. If thicker films are to be used for magnetooptic memory applications, they should possess larger wall-motion fields than the films investigated, in order to achieve stable spots. The erasure field of the spots was found to depend on the strength of the applied writing field and on the duration and the power of the heating laser pulse. A writing-erasing hysteresis was recorded by means of the Faraday effect. A thermal saturation field is introduced and measured in dependence on film thickness for LTP films. With the help of this field and wall-pinning effects, thermomagnetic writing in MnBi films is discussed.     

Magneto-optic insulators utilizing the optical activity of Co++(Td)

Large magneto-optic effects are associated with the crystal field transitions of Co++(Td) in a variety of spinel oxides. In the oxides, the F and P crystal field bands peak at about 1.5 and 0.6 μm, respectively. Many iron-containing quaternary compounds (CoTxFe2-xO4) have transition temperatures above ambient. Here, T is a trivalent metal ion such as Cr³⁺or Rh³⁺. Room-temperature magneto-optic measurements on a number of these compounds indicate peak Faraday effects in the range of 0.5 × 10⁵to 1.0 × 10⁵(deg/cm) at about 0.6 μm. The Curie temperature may be adjusted by the compositional parameter x and normal remanence of the surface Kerr effects are observed. The latter properties are potentially useful for optical memory devices. These materials are considered for isolation and modulation devices in the 5.0 to 12.0 μm wavelength range.     

Photoconductivity, photovoltaic effect and photoluminescence in chemically deposited films of (Cd0.95–Pb0.05)S:CdCl2,Gd

Results of XRD, optical absorption spectra, photoconductivity, photovoltaic effect and photoluminescence are reported for (Cd_0.95–Pb_0.05)S:CdCl₂,Gd films prepared by chemical deposition technique at 60 °C and room temperature (RT). The XRD studies show prominent diffraction lines of CdS and PbS. Optical absorption spectra show direct bandgap nature with decreasing value due to addition of PbS. The saturated photocurrent (I_pc) to dark current (I_dc) ratios 10⁷ are found in films prepared at 60 °C and 10⁴ in films prepared at RT. Photoluminescence is found to be brighter in films prepared at RT. Photovoltaic efficiency 5% has been observed in such films.     

Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y₃Fe₅O₁₂ (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd₃Ga₅O₁₂ as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi₂O₃–B₂O₃ fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM_s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi_0.37Yb_2.63Fe₅O₁₂ LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi³⁺ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb³⁺ ions and Y³⁺ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.     

Growth and properties of the CuInS2 thin films produced by glancing angle deposition

We use the glancing angle deposition technique (GLAD) to grow CuInS₂ thin films by a vacuum thermal method onto glass substrates. During deposition, the substrate temperature was maintained at 200 °C. Due to shadowing effect the oblique angle deposition technique can produce nanorods tilted toward the incident deposition flux. The evaporated atoms arrive at the growing interface at a fixed angle θ measured from the substrate normal. The substrate is rotated with rotational speed ω fixed at 0.033 rev s^− 1. We show that the use of this growth technique leads to an improvement in the optical properties of the films. Indeed high absorption coefficients (10⁵–3.10⁵ cm^− 1) in the visible range and near-IR spectral range are reached. In the case of the absence of the substrate rotation, scanning electron microscopy pictures show that the structure of the resulting film consists of nanocolumns that are progressively inclined towards the evaporation source as the incident angle was increased. If a rapid azimuthal rotation accompanies the substrate tilt, the resulting nanostructure is composed of an array of pillars normal to the substrate. The surface morphology show an improvement without presence of secondary phases for higher incident angles (θ > 60°).     

Magnetooptical memory experiments on a rotating Mn-Cu-Bi disk medium

A thin film of a new magnetooptical memory medium, Mn-Cu-Bi, was prepared on a glass disk and their dynamic memory characteristics were examined with an experimental rotating disk exerciser. The Curie temperature of the medium was about 200°C. Curie-point writing was made on it. The written information was read by the Kerr effect. The Kerr rotation was ±1.3° at an Ar ion laser wavelength of 5145 Å, where the Kerr rotation of the medium was made maximum by an SiO overcoating. For track selection, a moving coil with a linear motion air bearing, whose shaft was rectangular in form, was used. By utilizing a laser for the light source of a moiré fringe measurement technique, an accurate track access was made possible. The accuracy was within 1 μm and the track-to-track transfer time was about 5 ms. Writing and reading were accomplished under computer control with the direct memory access mode. A 5.09 × 10^-6medium error rate without error correction was obtained for a 2.5 × 10⁵bit/cm²packing density at a data transfer rate of 0.5 MHz.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Comparison of Bi3Fe5O12 film giant Faraday rotators grown on (111) and (001) Gd3Ga5O12 single crystals

Bismuth iron garnet (Bi₃Fe₅O₁₂, BIG) epitaxial thin films were grown on single crystal (Gd₃Ga₅O₁₂, GGG) (111) and (001) substrates by rf-magnetron sputtering technique. Processing parameters have been optimized to obtain high deposition rate (2.74 μm/h) and the surface rms roughness less than 10 nm. X-ray diffraction reveals films epitaxial quality: exclusive (111) or (001) orientation with narrow rocking curves and strong in-plane texture. Films possess low optical loss and magneto-optical Faraday rotation (FR) as high as 5 deg/μm at 677 nm wavelength. Comparative analysis of films grown on (111) and (001) substrates clearly shows significant superiority of BIG/GGG(001) film. For this film, the coercive field ∼100 Oe appears to be 2.5 times lower while the optical transmission to be 10% higher than that for BIG/GGG(111) film. Enhanced magneto-optical performance of BIG/GGG(001) films relies upon better accommodation of the film-to-substrate mismatch strain through the tetragonal BIG lattice distortions compared to the rhombohedral one in BIG/GGG(111) films.     

Neutron irradiation of Nb3Sn and NbTi multifilamentary composites

NbTi and Nb3Sn multifilamentary composites have been irradiated with fast-neutrons at 60 ± 5°C to fluences of 1.2×10²⁰n/cm²(E > 1 MeV). The NbTi samples show only a moderate reduction of Icas a function of neutron fluence in an applied field of 40 kG. Reductions in Icwere observed for fluences greater than 3 × 10¹⁷n/cm²and saturate at 18% for fluences greater than 3-4 × 10¹⁹n/cm². The Nb3Sn composites showed large neutron radiation induced changes in Tc, Icand Hc2. Reductions in Tcwere observed for fluences greater than 7 × 10¹⁷n/cm². No measurable changes in Ic(40 kG) were observed below 10¹⁸n/cm². Between 2 and 3×10¹⁸n/cm², however, there is an apparent threshold where a very rapid reduction in Ic(40 kG) is initiated. At the threshold the decrease in Tcis 13%. Between the threshold and 1.1 × 10¹⁹n/cm², I2(40 kG) has been reduced to 4% of the unirradiated value. These changes in superconducting properties in NbTi and Nb3Sn are analyzed in terms of the radiation induced defects. The impact of the response to irradiation of both materials on their applications in fusion reactor magnets is discussed.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Magnetic properties and structure of cobalt-platinum thin films

The magnetic properties of RF sputtered Co-Pt alloy thin films were studied as a function of Pt content from 0 to 80 at%. At room temperature, ferromagnetic films were obtained in the range 0-32 and 40-80 at% Pt. For Pt contents between 32 and 40 at%, discontinuities in the magnetization, magnetostriction, and coercivity versus Pt content were observed; however no discontinuity was observed in the resistivity. The structure of films containing about 25 at% Pt is a mixture of hexagonal and face-centered cubic (FCC) phases. At this composition the magnetostriction is small, but coercivities are large-700 to 2000 Oe-and dependent upon film thickness. The coercivities of these films do not change with heat treatment up to temperatures of 600°C but decrease markedly at 700°C. The properties of equiatomic Co-Pt film s are similar to those of bulk alloys. In particular the large coercivity observed in films after heal treatment at 500° to 700°C is due to the formation of an ordered tetragonal phase within the face-centered cubic matrix. The structure of films of about 75 at% Pt is initially a disordered face-centered cubic phase and with heat treatment beginning at 500°C an ordered face-centered cubic phase forms. The coercivity of these films (∼200 Oe) does not change with annealing at 500°C. It decreases slightly upon further annealing at 600°C to 700°C. Electron microscope observations were used to correlate the magnetic properties with film structure.     

The crosstie memory

The crosstie memory stores information in magnetic domain walls in permalloy films about 350 Å thick. The domain walls are also used as shift register tracks. Serrated edges on narrow thin film permalloy strips are used to center a domain wall in each strip and to provide stable positions for crossties and Bloch lines. A magnetoresistance detector uses the same information bearing permalloy film as the magnetoresistive element. The entire crosstie memory can be fabricated on a silicon wafer or chip using conventional photolithographic procedures as are used in fabricating integrated circuits. Thus, a magnetic memory can be combined with semiconductor drivers, decoders, and sense amplifiers on the same chip. The memory is intended to serve as a block oriented random access memory (BORAM). Important background information such as static and dynamic stability conditions, Bloch line mobility, propagation and observation techniques are reviewed. Also, design goals and the role such device is expected to play in memory technology are presented. Anticipated performance includes a shift rate of 20 × 10⁶bits/sec, a bit density greater than 1.5 × 10⁵bits/cm², an operating temperature range from -50 °C to 100 °C, nonvolatility, low cost, and low power consumption.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Measurement of the diffusion coefficient of rare earth species in PbO-B2O3 flux used for liquid phase epitaxial growth of magnetic garnet films

The solute diffusion coefficient in a PbO-B₂O₃ flux system used for the growth of magnetic garnet films has been measured by two different techniques and found to be (5±1.5)×10^?7 cm²/sec in the growth temperature range of 840°C–887°C. In the first technique, for a nearly stagnant melt, the film thickness is proportional to the square root of the growth time after subtraction of the residual effects of convection. In the second technique the melt is stirred by rotating the substrate. The growth rate is constant after an initial transient, and is proportional to the square root of the rotation rate.     

Influence of R1parameter {=Fe2O3/(Y2O3+ Sm2O3+ Lu2O3)} on magnetic bubble properties of (YSmLuCa)3(FeGe)5O12

The influence of R1{=Fe2O3/(Y2O3+Sm2O3+Lu2O3)} in the melt composition on film properties, and growth characteristics, has been investigated for (YSmLuCa)3(FeGe)5O12. The garnet phase is the primary phase when R1is kept between 10 and 60. The temperature coefficient for the bubble collapse filed changes from -0.29 to -0.19 %/°C, and the growth rate with 10°C supercooling changes from 0.60 to 0.15 μm/min, by increasing R1=10 to 60. Distribution coefficients, K^Y, K^Sm, K^Luand K^Geincrease, and K^Feand K^Cadecrease, with increasing R1.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.