Structural and magnetic properties of epitaxial SnFe2O4 thin films

Epitaxial thin films of SnFe₂O₄ are deposited on sapphire substrate by ablating the sintered SnFe₂O₄ target with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). X-ray diffraction study reveals that SnFe₂O₄ films are epitaxial along (222) direction. The optical bandgap of SnFe₂O₄ film is estimated using transmittance vs. wavelength data and is observed to be 2.71 eV. The presence of hysteresis loop at room temperature in magnetization vs. field plot indicates the ferromagnetic behavior of the film. It is observed that the coercive field and remnant magnetization decrease with increase in temperature.     

Effect of PbO-SiO2 and PbO-B2O3 flux systems on the crystalline and magnetic properties of Ni0.5Zn0.5Fe2O4 ferrite prepared from the mixed powders

Lead borate and lead silicate were added to lower the sintering temperature of a Ni_0.5Zn_0.5Fe₂O₄ ferrite prepared from the blend of two types of powders and to homogenize the grain size. 5PbO·SiO₂ and 5PbO·B₂O₃ flux systems were added to lower the sintering temperature and diminish the magnetic loss at high frequencies. The ferrites were studied by bulk density, scanning electron microscopy and impedance analysis. It was found that the addition of PbO markedly accelerated the grain growth, while SiO₂ and B₂O₃ were found to be effective to obstruct the movement of grain boundaries and to minimize the grain size. Doping with PbO in the mixed powders appropriately increased the densification and initial permeability. The ferrite doped with 1% of 5PbO·SiO₂ possessed the lowest loss tangent (tgδ) in the range of 5 M-40 MHz and the highest threshold frequency.     

Gallium concentration effects on magnetic bubble films of EuTm2(Fe,Ga)5O112 garnet grown by liquid phase epitaxy

By varying the Ga concentrations x of EuTm₂Fe_5?xGa_xO₁₂ from x = 0 to about 0.8, thin magnetic films supporting stable bubbles with diameters from 0.5 to about 8μm, respectively, are deposited epitaxially onto gadolinium gallium garnet substrates oriented (111). For low values of x, the Ga segregation coefficient is about 2 and it decreases slightly as x increases. Thus, films contain roughly twice as much Ga as the LPE fluxed melts in which they grow. Both the characteristic length and magnetic bubble stability factor (Q) increase rapidly with x and, to a lesser degree, so does the uniaxial anisotropy field H_A while both 4πM and the uniaxial anisotropy K_u decrease.     

Chemistry of post-annealing of epitaxial CoFe2O4 thin films

CoFe₂O₄ thin films of different thicknesses were grown on SrTiO₃ substrates. The X-ray diffraction analysis and atomic force microscopy indicated both epitaxy and a granular microstructure. We studied the magnetic properties of these films as a function of oxygen post-annealing and film thickness. All as-deposited films exhibited similar magnetic properties with saturated magnetization (M_s) of approximately 50% of the bulk M_s, (80 Am² kg^− 1). After the post-annealing the M_s changes as a consequence of crystallographic restructuring of the film. Cation ordering in 100 nm thick films reduces M_s, whereas re-oxidation increases M_s for thinner films. 13 nm films, annealed for 1 h, reach the bulk M_s. For even thinner films the quantum-size effect reduces M_s. For a synthesis of ≥ 30 nm films an annealing cycle after deposition of every 15 nm layer is recommended.     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.     

Application of the wanklyn model to the BaOBaF2B2O3Y2O3Fe2O3 flux system

Data on the BaOBaF₂ B₂O₃ Y₂O₃ Fe₂O₃ flux system are analyzed in terms of the model recently proposed by Wanklyn, verified thus far for lead- and alkali- based fluxes. The model is found to hold, with the noticeable exception that in this particular case the basic oxide and the corresponding fluoride are not equivalent from the standpoint of phase equilibria: on the contrary, a BaF₂ addition makes “ineffective” a small but definite fraction of the BaO present in the melt.     

Magnetic properties and critical currents of epitaxial YBa2Cu3O7-x films

The authors report results of magnetic and transport measurements on thin epitaxial films of YBa₂Cu₃O_7-x which show critical current densities of 10⁷ A/cm² at 4.2 K. They exhibit well-formed symmetrical hysteresis loops and flux-trapping effects and linear susceptibilities at low fields. Magnetic and transport critical currents are in good agreement at low temperatures. The above properties are attributed to strong pinning from point defects which are suggested to be more numerous in films than in bulk single crystals. Diamagnetic shielding effects can be very large and are proportional to the critical current at zero field; however, there is a large penetration of H_a at all field values. Field-cooled magnetization is always very small, being only a few percent of the diamagnetic shielding. This small value is attributed to a balance between trapped flux and expelled flux in the cooling process. The strong pinning in attributed to a high density of defects in the film     

Electrodeposition and characterization of CaF2 and rare earth doped CaF2 films

Calcium fluoride (CaF₂) and the rare earth doped CaF₂ films have been electrodeposited on indium tin oxide (ITO) electrode through electrochemical generation of acid in aqueous solutions near room temperature. For CaF₂ film electrodeposition, the local pH at ITO surface is lowered by the electrochemical oxidation of ascorbate anion, and then the Ca-ethylene diamine tetraacetic acid disodium complexes which are close to the ITO electrode are decomposed to release free Ca²⁺ to react with F⁻to form CaF₂ deposit onto ITO. In the same way, RE-doped CaF₂ films have been electrodeposited onto ITO electrode. The morphology of films studied by scanning electron microscopy revealed that they are agglomerated and dense. The films showed a little [111] preferred orientation by X-ray diffraction. It was also proved that doped RE ions were distributed homogeneously in the film by energy dispersive spectroscopy mapping. The optical properties of the electrodeposited CaF₂, CaF₂:Eu and CaF₂:Tb films were studied by photoluminescence, and all films exhibit intense emission peaks.     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

Grain growth mechanisms in a spray-formed Ni3Al/Al2O3 composite in the presence of a liquid phase

Grain growth in the two-phase (liquid + solid) region of Ni₃Al reinforced with 0.8 vol.% Al₂O₃ participates synthesized by a spray atomization and co-injection technique was investigated. The grain growth of the as-sprayed and hot isostatically pressed (HIPed) materials in the two-phase region was found to be consistent with cube law kinetics, i.e., grain growth exponent was approximately 3. The activation energy for grain growth for the as-sprayed material was determined to be 308 ± 19 kJ mol⁻¹ while that of the HIPed material was calculated to be 327 ± 23 kJ mol⁻¹. The activation energy for grain growth was not a function of the amount of liquid phase or the composition of the liquid. Furthermore, the activation energy for grain growth was higher than that for diffusion through the liquid phase, suggesting that the mechanism for grain growth of the as-sprayed and HIPed Ni₃Al composite in the two-phase region was controlled by an interface reaction. The role of the second-phase Al₂O₃ particles on grain growth for the as-sprayed and HIPed Ni₃Al materials was not significant.     

Chemical vapor deposition growth of Fe3O4 thin films and Fe/Fe3O4 bi-layers for their integration in magnetic tunnel junctions

A possible route for the synthesis of Fe₃O₄, Fe, and Fe/Fe₃O₄ bi-layers with chemical vapor deposition by employing the same Fe₃(CO)₁₂ carbonyl precursor is presented. The comprehensive structural, chemical, and morphological investigation of the as-deposited thin single films and bi-layers is performed by X-ray diffraction, X-ray reflectivity, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry depth profiling. We present the possibility of performing the deposition of pure metallic Fe and Fe₃O₄/γ-Fe₂O₃ by adjusting the deposition pressure from 10^- 3/^- 4 Pa to 1 Pa, respectively. The integration of Fe₃O₄ thin films in a magnetic tunnel junction stack fully synthesized by in situ atomic layer and chemical vapor deposition processes is also presented, showing good stack stability and marginal interdiffusion.     

Measurement of the current transient in Ta2O5 films

Current vs. time (I−t) measurements were performed on Ta₂O₅-based devices. Charge build-up at the Ta₂O₅/SiO₂ interface was used to explain the transient. The interfacial charge density was calculated from the I−t curve and the maximum was found to be 398 nC cm^-2 and 317 nC cm^-2 for Al/Ta₂O₅/Si and Al/Ta₂O₅/SiO₂/Si capacitors respectively. The value for MTOS was comparable with the value obtained by quasi-static measurements.     

Frequency and temperature dependence of the millimeter wave conductivity of epitaxial YBa2Cu3O7 films

A millimeter wave spectrometer for frequencies between 100 and 350 GHz consisting of continuously tunable backward wave oscillators as sources and a quasioptical interferometer in the Mach-Zehnder configuration was used to measure the transmittivity in phase and amplitude of YBa₂Cu₃O₇ thin films on NdGaO₃ substrates. From the measured spectra we derived the real and imaginary part of the dynamic conductivity= ₁+i ₂ in the superconducting state as a function of temperature. The ₁(T) and ₂(T) values at 300 GHz were compared to corresponding values at 19 GHz determined by surface impedance measurements of the same films using a shielded dielectric resonator. Our observed frequency dependence of both ₁(T) and ₂(T) is consistent with a strong reduction of the quasiparticle scattering rate ^–1(T) with decreasing temperature belowT _c .     

Ozone sensing using In2O3-modified Ga2O3 thin films

It is shown that at elevated temperatures the conductance of an In ₂O₃-modified Ga₂O₃ thin film depends significantly and reversibly on the ozone concentration in the ambient air. This ozone sensitivity is much greater than with pure Ga ₂O₃ or In₂O₃ thin films, respectively. The ozone sensitivity of the In₂O₃-modified Ga₂O₃ thin film is characterized by an impressive selectivity, and is maximal at an operation temperature of about 600°C. The cross sensitivities to other gases present in ambient conditions are small compared to the ozone sensitivity, thus opening the way to use this system for ambient ozone monitoring. The results are discussed using an electron injection model     

Structural and optical analysis of nanocrystalline thin films of mixed rare earth oxides (Y1-xErx)2O3

Nanocrystalline thin films of mixed rare earth oxides (Y_1-xEr_x)₂O₃(0.1 ≤ x ≤ 1) were deposited by electron beam evaporation technique on polished fused silica glass at different substrate temperatures (200-500 °C). The effect of the substrate temperature as well as the mixing parameter (x) on the structural and optical properties of these films has been investigated by using X-ray diffraction (XRD), energy dispersive x-ray analysis and optical spectrophotometry. XRD investigation shows that mixed rare earth oxides film (Y_1-xEr_x)₂O₃ grown at lower substrate temperature (T_s ≤ 300 °C) are poorly crystalline, whereas films grown at higher substrate temperatures (T_s ≥ 400 °C) tend to have better crystallinity. Furthermore, the mixing parameter (x) was found to stabilize the cubic phase over the entire of 0.1 ≤ x ≤ 1. The crystallite size of the films was found to vary in the range from 25 to 39 nm. Optical band gap of the films was deterimined by analysis of the absoprtion coeffifcient. For films deposited at different substrate temperatures direct and indirect transitions occur with energies varied from 5.29 to 5.94 eV and from 4.23 to 4.51 eV, respectively. However, films of different composition x, give optical band gap varied from 6.14 to 5.86 eV for direct transition and from 5.23 to 4.22 eV for indirect transitions. Consequently, one may conclude that it is possible to tune the energy band gap by relative fraction of constituent oxides. It was found that optical constants increase with increasing the substrate temperature. Nevertheless, the values of n and k decrease with increasing the mixing parameter, x.     

Quantitative analysis of lattice disorder and superconducting transition in epitaxial YBa2Cu3O6.9 films

We show that the average lattice disorder in YBa₂Cu₃O_6.9 films grown by ion-beam sputtering is homogeneous and can be quantified by introducing the lattice coherence lengthr _c that is extracted from the width of X-ray diffraction rocking curves. The superconducting properties of the films are correlated withr _c T _c decreases with increasing disorder forT _c 10 nm, while the width of the resistive transition and the normal-state resistivity increase.     

High-resolution and analytical transmission electron microscopy of epitaxial YBa2Cu3O7−x thin films and YBa2Cu3O7/PrBa2Cu3O7 superlattices

Transmission electron microscopy (TEM) studies of epitaxial YBa₂Cu₃O_7−x thin films and YBa₂Cu₃O₇/PrBa₂Cu₃O₇ superlattices are summarized. High-resolution imaging of cross-sections and plan views and energy-dispersive X-ray microanalysis and electron energy loss spectroscopy in the transmission electron microscope were the methods applied. In the first section results on YBa₂Cu₃O_7−x thin films With varying oxygen stoichiometry deposited onto SrTiO₃ are discussed. Then, YBa₂Cu₃O₇/PrBa₂Cu₃O₇ superlattices deposited onto SrTiO₃ and MgO are investigated. Finally, an interface analysis of high-quality YBa₂Cu₃O_7−x thin films deposited onto sapphire with yttrium-stabilized zirconia buffer layers is presented.     

铁电相BiFeO3对多铁复合薄膜CoFe2O4-BiFeO3铁磁性能的影响

为了研究铁电相BiFeO₃对复合薄膜磁性能的影响,在LaNiO₃ (LNO)缓冲层的Si (100)衬底上旋涂制备了含有0、6、9、10层等不同厚度BiFeO₃的层状CoFe₂O₄-BiFeO₃ (CFO-BFO) 多铁复合薄膜。采用XRD、SEM以及TEM对其结构和形貌进行了表征,采用振动样品磁强计测量磁性,研究了不同厚度BFO对复合薄膜磁性的影响。结果表明: CFO和BFO在异质结构薄膜中共存。缓冲层LNO和铁磁相CFO薄膜具有精细微观结构及明显界面。铁电相BFO的厚度对CFO-BFO复合薄膜的磁性能产生了很大影响。在含有不同层数铁电相BFO的复合薄膜中,含有9层BFO复合薄膜的饱和磁化强度最大,达到了230 emu·cm^-3,相比无铁电相BFO的薄膜,饱和磁化强度提高了18.6%。初步讨论认为: 随着铁电相BFO厚度的增加,CFO与BFO之间的应力传导引起了复合薄膜饱和磁化强度的提高。