Spin gapless semiconductor like Ti2MnAl film as a new candidate for spintronics application

A novel Heusler ferrimagnet Ti₂MnAl film has been grown on Si(001) substrate using magnetron sputtering. Characteristics of its magnetic and transport properties reveal the spin‐gapless‐semiconductor (SGS) nature of the stoichiometric Ti₂MnAl, in agreement with theoretical prediction. The as‐grown SGS‐like Ti₂MnAl film demonstrated high Curie temperature, nearly compensated ferrimagnetic properties with small coercivity and low magnetization. It also showed semiconductor‐like behavior at room temperature allowing good compatibility with commercial Si‐based semiconductor. In this regards, Ti₂MnAl film is a potential candidate material for spintronics application, especially for the minimization of energy consumption of device. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Optical properties of MnAl films

The optical properties of MnAl films of different compositions, deposited at different substrate temperatures and in the thickness range 25 to 90 nm, are reported. The reflectance and transmittance are measured in the wavelength range 320–900 nm for near normal incidence of light. These measurements are used to calculate the optical constants namely, refractive index (n) and extinction coefficient (k). The wavelength and thickness dependence of these optical constants are reported. The optical measurements for films with higher Mn content and grown at higher substrate temperature reveal that n and k values are constant over a wide wavelength range (500–900 nm) showing high reflectance in the visible and near infrared region.     

0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices with compositionally undulating step-graded InAsyP1-y buffers

Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulating stepgraded InAsyP1-y buffer layers with a lattice mismatch of ～1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate.With an optimized buffer thickness,the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion.High-performance single-junction devices are demonstrated,with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2,which are measured under the standard solar simulator of air mass 1.5-global(AM 1.5 G).     

L10 Stacked Binaries as Candidates for Hard‐Magnets: FePt,MnAl and MnGa

We present a novel approach for designing new hard magnets by forming stacks of existing binary magnets to enhance the magneto crystalline anisotropy. This is followed by an attempt at reducing the amount of expensive metal in these stacks by replacing it with cheaper metal with similar ionic radius. This strategy is explored using examples of FePt, MnAl and MnGa. In this study a few promising materials are suggested as good candidates for hard magnets: stacked binary FePt₂MnGa₂ in structure where each magnetic layer is separated by two non‐magnetic layers, FePtMnGa and FePtMnAl in hexagonally distorted Heusler structures and FePt_0.5Ti_0.5MnAl.     

Effect of CoSi2 buffer layer on structure and magnetic properties of Co films grown on Si（001） substrate

Buffer layer provides an opportunity to enhance the quality of ultrathin magnetic films.In this paper,Co films with different thickness of Co Si2buffer layers were grown on Si(001)substrates.In order to investigate morphology,structure,and magnetic properties of films,scanning tunneling microscope(STM),low energy electron diffraction(LEED),high resolution transmission electron microscopy(HRTEM),and surface magneto-optical Kerr effect(SMOKE)were used.The results show that the crystal quality and magnetic anisotropies of the Co films are strongly affected by the thickness of Co Si2buffer layers.Few Co Si2monolayers can prevent the interdiffusion of Si substrate and Co film and enhance the Co film quality.Furthermore,the in-plane magnetic anisotropy of Co film with optimal buffer layer shows four-fold symmetry and exhibits the two-jumps of magnetization reversal process,which is the typical phenomenon in cubic(001)films.     

Effects of underlayer materials and substrate temperatures on the structural and magnetic properties of Nd2Fe14B films

Thin films of Nd_2Fe_{14}B were fabricated on heated glass substrates by dc magnetron sputtering. Different material underlayers (Ta, Mo, or W) were used to examine the underlayer influence on the structural and magnetic properties of the NdFeB films. Deposited on a Ta buffer layer at 420℃, the 300 nm thick NdFeB films were shown to be isotropic. But when the substrate temperature T_s was elevated to 520℃, the Nd_2Fe_{14}B crystallites of (00l) plane were epitaxially grown on Ta (110) underlayer. In contrast, Mo (110) buffer layer could not induce any preferential orientation in NdFeB film irrespective of the substrate temperature or film thickness. The W buffer layer was found to be most effective for the nucleation of Nd_2Fe_{14}B crystallites with c-axis alignment perpendicular to the film plane when T_s<490℃. But at T_s=490℃ the magnetic layer became isotropic. The maximum coercivity obtained was about 995 kA/m for the 100nm film deposited on W underlayer at 490℃. These variations were tentatively explained in terms of the lattice misfit between the underlayer and the magnetic layer, combined with the considerations of underlayer morphologies.     

Research on CeO2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.     

不同粒径纳米Y2Ba4CuBiOy 相掺杂对TSIG法单畴YBCO超导块材性能的影响

本文采用顶部籽晶熔渗方法(TSIG), 研究了不同粒径纳米Y₂Ba₄CuBiO_y粒子对单畴YBCO超导块材的生长形貌、微观结构及其磁悬浮力的影响.实验所用纳米Y₂Ba₄CuBiO_y粉体的平均粒度分别为283.0 nm, 170.4 nm以及82.5 nm, 每种粉体在YBCO超导块材中的含量均为2 wt%. 研究结果表明: 在掺杂量为2 wt%的情况下, Y₂Ba₄CuBiO_y粉体的粒度并不影响样品的宏观形貌, 均可制备出单畴YBCO块材; 并且成功地将纳米Y₂Ba₄CuBiO_y粒子引入单畴YBCO块材中, 且使其均匀分布, 但样品中的Y₂Ba₄CuBiO_y粒子均小于其初始粉体的粒度, 分别减小到270 nm, 150 nm和50 nm; 随着Y₂Ba₄CuBiO_y粉体初始粒度的减小, 样品的磁悬浮力逐渐增大, 分别为10 N, 17 N, 22 N. 该结果为进一步研究纳米磁通钉扎中心的引入方法及提高YBCO超导块材的性能有重大意义.     

择优取向MgO缓冲层上制备的硅基Ba0.7Sr0.3TiO3薄膜的结构和性能研究

分别采用sol-gel法和磁控溅射法在Si（001）单晶衬底上制备出（111）和（001）取向的MgO缓冲层薄膜,随后在其上生长Ba_0.7Sr_0.3TiO₃（BST30）铁电薄膜.通过X射线衍射,扫描电子显微镜,原子力显微镜等方法研究了薄膜的微结构.实验结果发现,在较厚的MgO（001）缓冲层上可长出（101）取向的BST30薄膜,而在较薄的MgO（111） 缓冲层上则表现出（101）和（111）取向相互竞争的现象,随着MgO（111）缓冲 关键词： 0.7Sr_0.3TiO₃')" href="#">Ba_0.7Sr_0.3TiO₃ 铁电薄膜 择优取向 sol-gel     

Effect of microstructure on thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi₂Sr₂Co₂O_y thin films with different microstructures have been prepared by chemical solution deposition on LaAlO₃(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the seebeck coefficient due to the enhanced energy filtering effect of small-grain film. The nanostructured Bi₂Sr₂Co₂O_y film with the average grain size of about 100 nm shows a power factor comparable to that of the films with larger grains. Since the thermal conductivity of the nanostrcutured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi₂Sr₂Co₂O_y thin film with grains in nanometer size.     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

Growth and characterization of crystalline gadolinium oxide on silicon carbide for high- application

We have investigated the growth and electrical properties of crystalline Gd₂O₃ grown on 6H-SiC(0001) substrates by molecular beam epitaxy. Initially, Gd₂O₃ islands with hexagonal structure were formed. Further growth resulted in the formation of flat layers in a mixture of [111]-oriented cubic bixbyite and monoclinic structure. The fabricated capacitors with 14 nm Gd₂O₃ exhibited suitable dielectric properties at room temperature; such as a dielectric constant of ε=22, a leakage current of 10⁻⁸ A/cm²@1 V and breakdown fields >4.3 MV/cm.     

Structural,optical and gas sensing properties of Cu2O/CuO mixed phase: effect of the number of coated layers and (Cr + S) co-Doping

Thin films of Cu₂O/CuO mixed phase have been deposited on pre-cleaned glass substrate by a spin-coating technique. The influence of Cr-doping, (Cr?+?S) co-doping and the number of coated layers on the structures and optical behaviors of the films were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, and UV-Visible spectroscopies. From XRD, FTIR and Raman results; the films are composed of polycrystalline monoclinic CuO and cubic Cu₂O phases with crystallite sizes ranged from 10.05 to 23.08?nm. Increasing the thickness improves the films’ crystallinity and decreases the defects level in the films. Cr and S incorporation encourages the growth of CuO phase at the expense of Cu₂O one and affects the preferred growth direction. The doping with Cr and S blue shifted the B_g mode and multi-phonon transitions. The direct and indirect optical band gaps decreased from 2.25?eV and 1.60?eV to 2.10?eV and 1.20?eV by growing the number of deposited layers from 2 to 8 layers. The film sensitivity towards CO₂ at different gas flow rate was studied and compared with those of similar systems. Also; response time, recovery time, detection limit, and limit of quantification are estimated.     

The epitaxial growth of BaSnO3 buffer layer on IBAD-MgO template and its effects on GdBa2Cu3O7−δ film: A preliminary study

We report a successful fabrication of c-axis oriented GdBa₂Cu₃O_7−δ (GdBCO) films on the BaSnO₃ (BSO) buffer layers on ion-beam assisted deposition (IBAD)-MgO template by pulsed-laser deposition (PLD). The (0 0 l) growth and in-plane textures of BSO buffer layers were found sensitive to the substrate temperature (T_s). With increasing the BSO layer thickness up to ∼165 nm, in-plane texture (Δ? ∼ 6.2°) of BSO layers was almost unaltered while completely c-axis oriented BSO layers were obtainable from samples with the thickness below ∼45 nm. On the BSO buffer layers showing in-plane texture of 6.2° and RMS surface roughness of ∼8.6 nm, GdBCO films were deposited at 780–800 °C. All GdBCO films exhibited Δ? values of 4.6–4.7°, T_c,zero of ∼91 K, and critical current density (J_c) over 1 MA/cm² at 77 K in a self-field. The highest J_c value of 1.82 MA/cm² (I_c of 51 A/cm-width) was achieved from the GdBCO film deposited at T_s of 790 °C. These results support that BSO can be a promising buffer layer on the IBAD-MgO template for obtaining high-J_c GdBCO coated conductors.     

CdTe太阳电池前电极SnO2:F/SnO2复合薄膜性能分析

减薄CdS窗口层是提高CdS/CdTe太阳电池转换效率的有效途径之一,减薄窗口层会对器件造成不利的影响,因此在减薄了的窗口层与前电极之间引入过渡层非常必要.利用反应磁控溅射法在前电极SnO₂:F薄膜衬底上制备未掺杂的SnO₂薄膜形成过渡层,并将其在N₂/O₂=4 ∶1,550 ℃环境进行了30 min热处理,利用原子力显微镜、X射线衍射仪、紫外分光光度计对复合薄膜热处理前后的形貌、结构、光学性能进行了表征,同时分析了复     

A polarised neutron study of magnetic moment density in Cu2MnAl

A polarised neutron study of the ferromagnetic Heusler alloy Cu₂Mn_0.863Al_1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn²⁺ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of the Cu atoms. No appreciable conduction electron polarisation is found.     

Specific features of the properties of half-metallic ferromagnetic Heusler alloys Fe<Subscript>2</Subscript>MnAl,Fe<Subscript>2</Subscript>MnSi,and Co<Subscript>2</Subscript>MnAl

The structural, magnetic, and electrical properties of half-metallic Heusler alloys Fe₂MnAl, Fe₂MnSi, and Co₂MnAl have been investigated in the temperature range of 4–900 K. According to the X-ray diffraction analysis, these alloys have the B2 and L2₁ structures with different degrees of atomic order. The magnetic state of the alloys is considered as a two-sublattice ferrimagnet. The electrical resistivity and thermoelectric power have been discussed in the framework of the two-current conduction model taking into account the existence of an energy gap in the electronic spectrum of the alloys near the Fermi level for the subband with spin-down (minority) electrons.     

Magnetotransport properties of epitaxial Pr0.5Ca0.5MnO3 films grown by a solution technique

Epitaxial Pr_0.5Ca_0.5MnO₃ films have been synthesized on (0 0 1) SrTiO₃ substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.     

YBa2Cu3O7-x涂层导体的外延生长和性能对CeO2缓冲层的依赖性

利用倾斜衬底沉积法在无织构的金属衬底上生长了MgO双轴织构的模板层,在这一模板层上实现了YBa₂Cu₃O_7-x薄膜的外延生长.在外延YBa₂Cu₃O_7-x薄膜前,依次沉积了钇稳定的立方氧化锆和CeO₂作为缓冲层.利用X射线衍射2θ扫描、扫描、Ω扫描和极图分析测定了这些膜的结构和双轴织 关键词： 2Cu₃O_7-x镀膜导体')" href="#">YBa₂Cu₃O_7-x镀膜导体 2缓冲层')" href="#">CeO₂缓冲层 厚度依赖性 外延生长     

A new method to preserve the c-axis growth of thick YBa2Cu3O7–δ films grown by pulsed laser deposition

YBa₂Cu₃O_7–δ (YBCO) films were prepared on (1 0 0) MgO substrates by pulsed laser deposition (PLD) method. In order to eliminate the a-axis growth, which is commonly observed in the YBCO film thicker than a critical value, we developed a new PLD target that was sintered at a temperature far below YBCO 123 phase formation. The surface analysis made by AFM technique confirmed that very fine particles of around 20 nm size could be ejected from the new target to the substrate. The fine oxide clusters could be easily moved and incorporated into the YBCO phase thus benefited the c-axis growth even in the thick films. For instance, only the c-axis growth in the new film with a thickness of about 650 nm was larger than a critical thickness of the a-axis growth. However, in the standard film of the same thickness, there is 24.5% of the a-axis growth accompanying the main c-axis growth. Therefore, the c-axis growth could be preserved in the very thick YBCO film by a non-superconducting target.