TbMnO3 epitaxial thin films by pulsed-laser deposition

Epitaxial TbMnO₃ films have been fabricated on SrTiO₃(001) and LaAlO₃(001) substrates by pulsed laser deposition (PLD), the structure and surface morphology of the films were characterized by X-ray diffraction with Cu K_α radiation and atomic force microscopy. The electrical transport and magnetic properties of the TbMnO₃ films and bulk were examined, the resistivity and the forbidden band width E_g change with epitaxial orientation, semiconductor transport properties are found in the films and bulk, the average of the E_g of the films on SrTiO₃ and on LaAlO₃ is equal to the E_g of the bulk. The two TMO films have different magnetization mode, the magnetization of the film on SrTiO₃ have an analogy to that of TbMnO₃ single crystal.     

Field dependence of spin and orbital moments of Fe in L10 FePt magnetic thin films

The field dependence of spin and orbital magnetic moments of Fe in L1₀ FePt magnetic thin films was investigated using X-ray magnetic circular dichroism (XMCD). The spin and orbital moments were calculated using the sum rules; it was found that the spin and orbital moment of Fe in L1₀ FePt films are ∼2.5 and 0.2 μ_B, respectively. The relative XMCD asymmetry at Fe L₃ peak on the dependence of applied field suggested that the majority magnetic moment of L1₀ FePt films resulted from Fe.     

PLD of Fe3O4 thin films: Influence of background gas on surface morphology and magnetic properties

Ablation of Fe₃O₄ targets has been performed using a pulsed UV laser (KrF, λ = 248 nm, 30 ns pulse duration) onto Si(100) substrates, in reactive atmospheres of O₂ and/or Ar, with different oxygen partial pressures. The as-deposited films were characterised by atomic force microscopy (AFM), X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS) and extraction magnetometry, in order to optimise the deposition conditions in the low temperature range. The results show that a background mixture of oxygen and argon improves the Fe:O ratio in the films as long as the oxygen partial pressure is maintained in the 10⁻² Pa range. Thin films of almost stoichiometric single phase polycrystalline magnetite, Fe_2.99O₄, have been obtained at 483 K and working pressure of 7.8 × 10⁻² Pa, with a high-field magnetization of ∼490 emu/cm³ and Verwey transition temperature of 112 K, close to the values reported in the literature for bulk magnetite.     

Parallel syntheses and thermoelectric properties of Ce-doped SrTiO3 thin films

Thermoelectric properties of single crystalline Ce_xSr_1−xTiO₃ films (0 ≤ x ≤ 0.5) have been studied by using combinatorial pulsed-laser deposition. Temperature gradient method was used for identifying an optimum growth temperature for SrTiO₃ homoepitaxial growth, at which both oxygen stoichiometry and persisting layer-by-layer growth mode could be accomplished. Electrical conductivity (σ) and Seebeck coefficient (S) were measured at room temperature for the composition-spread films grown at the optimized temperature and found to be considerably higher than those reported for bulk poly-crystalline compounds. Hall measurement revealed that carrier density linearly increased with increasing x, suggesting that a trivalent Ce ions substituted divalent Sr ions to supply electrons. A maximum power factor (S²σ) was obtained for the x = 0.2 film, being 7 and 14 μW/K² cm at 300 and 900 K, respectively.     

Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films

We have grown lead iron niobate thin films with composition Pb(Fe_1/2Nb_1/2)O₃ (PFN) on (0 0 1) SrTiO₃ substrates by pulsed laser deposition. The influence of the deposition conditions on the phase purity was studied. Due to similar thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN perovskite phase. By optimizing the kinetic parameters, we succeeded in identifying a deposition window which resulted in epitaxial perovskite-phase PFN thin films with no identifiable trace of impurity phases appearing in the X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were smooth and epitaxially oriented with the substrate and as demonstrated by RHEED streaks which were aligned with the substrate axes. X-ray diffraction showed that the films were completely c-axis oriented and of excellent crystalline quality with low mosaicity (X-ray rocking curve FWHM?0.09°). The surface roughness of thin films was also investigated by atomic force microscopy. The root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm for 100-nm-thick films. We also observe a correlation between grain size, surface roughness and film thickness.     

Preparation of transparent conductive TiO2:Nb thin films by pulsed laser deposition

This study investigated the optical and electrical properties of Nb-doped TiO₂ thin films prepared by pulsed laser deposition (PLD). The PLD conditions were optimized to fabricate Nb-doped TiO₂ thin films with an improved electrical conductivity and crystalline structure. XRD analyses revealed that the deposition at room temperature in 0.92 Pa O₂ was suitable to produce anatase-type TiO₂. A Nb-doped TiO₂ thin film attained a resistivity as low as 6.7 × 10⁻⁴ Ω cm after annealing at 350 °C in vacuum (<10⁻⁵ Pa), thereby maintaining the transmittance as high as 60% in the UV-vis region.     

Magnetoresistance of magnetite thin films grown by pulsed laser deposition on GaAs(1 0 0) and Al2O3(0 0 0 1)

Magnetotransport properties of magnetite thin films deposited on gallium arsenide and sapphire substrates at growth temperatures between 473 and 673 K are presented. The films were grown by UV pulsed laser ablation in reactive atmospheres of O₂ and Ar, at working pressure of 8 × 10⁻² Pa. Film stoichiometry was determined in the range from Fe_2.95O₄ to Fe_2.97O₄. Randomly oriented polycrystalline thin films were grown on GaAs(1 0 0) while for the Al₂O₃(0 0 0 1) substrates the films developed a (1 1 1) preferred orientation. Interfacial Fe³⁺ diffusion was found for both substrates affecting the magnetic behaviour. The temperature dependence of the resistance and magnetoresistance of the films were measured for fields up to 6 T. Negative magnetoresistance values of ∼5% at room temperature and ∼10% at 90 K were obtained for the as-deposited magnetite films either on GaAs(1 0 0) or Al₂O₃(0 0 0 1).     

Effect of composition on phase formation,microstructure and magnetic properties of Nd–Fe–B thin films

Nd–Fe–B hard magnetic thin films were deposited on a combined Cr/Ta buffer layer on heated MgO(1 0 0) substrates by pulsed laser deposition. The effect of composition on phase formation, morphology and magnetic properties was investigated. For a quantification of phase formation, hysteresis measurements along the hard axis are used. Optimum phase formation is obtained at a Nd/Fe ratio around 0.3. For this Nd content an excellent magnetic texture and a coercivity up to 1 T can be obtained; however, remanence is reduced and the films have a granular microstructure with high roughness. Also a certain B surplus is of benefit. However, with a too-high B or Nd surplus phase formation is more difficult.     

Epitaxial growth of Co(0 0 0 1)hcp/Fe(1 1 0)bcc magnetic bi-layer films on SrTiO3(1 1 1) substrates

Co(0 0 0 1)_hcp/Fe(1 1 0)_bcc epitaxial magnetic bi-layer films were successfully prepared on SrTiO₃(1 1 1) substrates. The crystallographic properties of Co/Fe epitaxial magnetic bi-layer films were investigated. Fe(1 1 0)_bcc soft magnetic layer grew epitaxially on SrTiO₃(1 1 1) substrate with two type variants, Nishiyama–Wasserman and Kurdjumov–Sachs relationships. An hcp-Co single-crystal layer is obtained on Ru(0 0 0 1)_hcp interlayer, while hcp-Co layer formed on Au(1 1 1)_fcc or Ag(1 1 1)_fcc interlayer is strained and may involve fcc-Co phase. It has been shown possible to prepare Co/Fe epitaxial magnetic bi-layer films which can be usable for patterned media application.     

Growth behaviour of ZnO thin films and nanowires on SrTiO3 substrates

We report on comparative investigations of ZnO thin films and nanowires grown on SrTiO₃ (STO) single crystal substrates. Using pulsed laser deposition technique, we could grow ZnO thin films with ()- and (0001)-orientations on (100)- and (110)-orientated STO substrates, respectively. ZnO nanowires, grown by vapour condensation method with Au catalyst layers, did not show preferential alignment on either of the STO substrates. When the ZnO(0001)/STO(110) film was used as seed layer, we obtained dense and vertically aligned nanowires. Whereas, few and inclined nanowires were grown on the ZnO()/STO(100) film. We discuss possible origins to cause all the observations.     

Pulsed laser deposition and characterization of multilayer metal-carbon thin films

Cobalt-DLC multilayer films were deposited with increasing content of cobalt, keeping carbon content constant by pulsed laser deposition technique. A cobalt free carbon film was also deposited for comparison. Excimer laser was employed to ablate the materials onto silicon substrate, kept at 250 °C, while post-deposition annealing at 400 °C was also performed in situ. The formation of cobalt grains within the carbon matrix in Co-DLC films can be seen through scanning electron and atomic force micrographs while no grains on the surface of the cobalt-free DLC film were observed. Raman spectra of all the films show D- and G-bands, which is a confirmation that the films are DLC in nature. According to Vibrating sample magnetometer (VSM) measurements, the DLC films with cobalt revealed ferromagnetic behaviour whereas the cobalt free DLC film exhibited diamagnetic behaviour. The pure DLC film also shows ferromagnetic nature when diamagnetic background is subtracted. Spectroscopic Ellipsometry (SE) analysis showed that the optical band gaps, refractive indices and extinction coefficients of Co-DLC films can be effectively tuned with increasing content of cobalt.     

Magnetic nanocomposite thin films of BaFe12O19 and TiO2 prepared by sol-gel method

The composite films with different weight ratio of barium ferrite to titanium dioxide are successfully prepared using sol-gel method for the first time. The morphology, crystal structure and magnetic properties of composite films are investigated with atomic force microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that the composite films are uniform with no microcracks. The grain diameters are less than 100 nm. With the increase of barium ferrite, the grain diameter decreases. The composite films are composed of M-type hexagonal barium ferrite and rutile titanium dioxide. The composite films possess the excellent magnetic properties. The specific saturation magnetization and coercivity reach 18.3 emu/g and 3350 Oe, respectively. The application of composite films in magnetic recording and electromagnetic absorption fields is promising.     

Epitaxial MnP thin films: epitaxial growth,magnetic and electrical properties

We have grown 500 Å MnP on undoped GaAs(1 0 0) substrate using solid-source molecular beam epitaxy. In order to characterize the crystal structure of MnP, we performed in-situ reflection high energy electron diffraction and θ–2θ XRD X-ray diffraction studies. From the measurements of superconducting quantum interference device, Quantum Design, MnP thin film shows ferromagnetic ordering at around 291.5 K. It shows a metallic resistivity in MnP thin film.     

Preparation and magnetoresistance of thin CrO2 films

Highly textured chromium dioxide (CrO₂) films have been deposited on Al₂O₃ single-crystal substrates by atmospheric pressure chemical vapor deposition method (CVD). X-ray diffraction patterns show that the CrO₂ films are (1 0 0)-oriented on Al₂O₃ (0 0 1) substrates, and are (1 0 1)-oriented on Al₂O₃ (0 1 2) substrates. Scanning electron microscopy images indicate that the (1 0 0)-oriented CrO₂ films grown on Al₂O₃ (0 0 1) substrates have smoother surface and better qualities than that grown on Al₂O₃ (0 1 2) substrate. At room temperature, the magnetoresistance of the (1 0 0)- and (1 0 1)-oriented CrO₂ films are nearly same, and both show a linear dependence on applied magnetic field. While at 80 K, the (1 0 1)-oriented CrO₂ films show a much larger magnetoresistance compared with the (1 0 0)-oriented CrO₂ films. The reasons are briefly discussed.     

Electric current-induced giant electroresistance in epitaxial La0.67Sr0.33MnO3 thin films

The electronic transport behavior of La_0.67Sr_0.33MnO₃ epitaxial thin films with different thicknesses has been investigated under various applied DC currents. The 20 and 70 nm thick films show a giant negative electroresistance (ER). In contrast, the films with 100 nm thickness show unusual giant positive ER, which can reach 30% with the current density of 1.8×10⁸ A/cm² at room temperature. It is interesting that the electric current can also change the magnetoresistance of the films. The results were explained by considering the spin polarized current induced increase of ferromagnetic metallic phase and current-induced lattice distortion via electron wind force under high current density.     

Magnetic and structural study of Cu-doped TiO2 thin films

Transparent pure and Cu-doped (2.5, 5 and 10 at.%) anatase TiO₂ thin films were grown by pulsed laser deposition technique on LaAlO₃ substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO₂. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to Cu substitutionally replacing cations in TiO₂.     

Optical characterization of PLD grown nitrogen-doped TiO2 thin films

Nitrogen-doped TiO₂ thin films were prepared by pulsed laser deposition (PLD) by ablating metallic Ti target with pulses of 248 nm wavelength in reactive atmospheres of O₂/N₂ gas mixtures. The layers were characterized by UV-VIS spectrophotometry and variable angle spectroscopic ellipsometry with complementary profilometry for measuring the thickness of the films. Band gap and extinction coefficient values are presented for films deposited at different substrate temperatures and for varied N₂ content of the gas mixture. The shown tendencies are correlated to nitrogen incorporation into the TiO_2-xN_x layers. It is shown that layers of significantly increased visible extinction coefficient with band gap energy as low as 2.89 eV can be obtained. A method is also presented how the spectroscopic ellipsometric data should be evaluated in order to result reliable band gap values.     

Electrodeposition and characteristics of Ni80Fe20/Cu composite wires

Electrodeposited Ni₈₀Fe₂₀/Cu composite wire has significant advantages over amorphous wire as sensing element for weak magnetic field sensors, such as orthogonal fluxgate sensors, due to its non-ferromagnetic and conductive core structure. In this study, the key processing parameters are investigated, including electrodeposition current density, duty cycle, electrolyte solution, pH value, applied magnetic field, effect of seeded layers, and post annealing.     

Pulsed laser deposition of (110) oriented semiconductive SrFeO3−x thin films

 The semiconductive perovskite-type oxide SrFeO_3-x (x<0.16) (SFO) thin films have been directly fabricated on (001)SrTiO₃ and (001)LaAlO₃ single crystal substrates by pulsed laser deposition(PLD) under high oxygen partial pressure of 100 Pa. The SFO thin films were (110) oriented. The x-ray photoelectron spectroscopy (XPS) analysis showed that the surface of SFO thin film has strong gas absorption capability. The resistance versus temperature has been measured in the temperature range from 77 K to 300 K. The SFO thin film showed typical semiconductive property. Dependence of resistance of SFO thin film on oxygen pressure was measured and result showed that the SFO thin film had better oxygen sensitive property. Received: 14 May 1996/Accepted: 15 August 1996     

Fabrication and magnetic properties of Ce1Y2Fe5O12 thin films on GGG and SiO2/Si substrates

Microstructure and magnetic properties of crystalline Ce₁Y₂Fe₅O₁₂ thin films prepared on GGG and on SiO₂/Si substrates by pulsed laser deposition were studied. The results show that highly textured Ce₁Y₂Fe₅O₁₂ film with (4 4 4) preferred orientation prepared on GGG (1 1 1) shows strong paramagnetism superimposed by a weak ferromagnetism. However, polycrystalline Ce₁Y₂Fe₅O₁₂ thin films on SiO₂/Si, which can only be obtained after post-annealing, show strong ferromagnetism with easy axis of magnetization lying in the plane of the film. With post-annealing temperature increasing, CeO₂ segregates from Ce₁Y₂Fe₅O₁₂; then YIG continues to be decomposed, forming Fe₂O₃. Consequently, the saturation magnetization of Ce₁Y₂Fe₅O₁₂ films decreases first and then increases correspondingly, which indicates that the magnetic properties of Ce₁Y₂Fe₅O₁₂ films are mainly related to the microstructure.