Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.     

Preparation and characterization of NiO, Fe2O3, Ni0.04Zn0.96O and Fe0.03Zn0.97O nanoparticles

Nickel oxide (NiO), iron (III) oxide (Fe₂O₃), and mixed oxide (Ni_0.04Zn_0.96O and Fe_0.03Zn_0.97O) nanoparticles were synthesized by modified sol–gel method. The nanoparticle structural and morphological properties were investigated by infrared spectroscopy (FTIR), X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), and Mössbauer spectroscopy. The mixed oxides were characterized by energy-dispersive X-ray spectroscopy (EDX). The oxide precursor powders were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The average sizes of the obtained NiO and Ni_0.04Zn_0.96O nanocrystallites were evaluated by X-ray line broadening using Scherrer's equation and were found to be 36 and 23 nm, respectively. Fe₂O₃ and Fe_0.03Zn_0.97O nanoparticles presented similar sizes, around 19 nm. EDX spectroscopy indicated that the calculated compositions of the mixed oxides were nearly consistent with their estimated molar ratios.     

The crystal structure of Ni5TiB2O10

The crystal structure of Ni₅TiB₂O₁₀ was determined by single crystal X-ray analysis. The compound has the same structure as the mineral ludwigite. The orthorhombic celldimensions and space group are $\text{a}\text{=9.206(7)}\text{A}\text{?}$, $\text{b}\text{=12.224(9)}\text{A}\text{?}$, $\text{c}\text{=2.994(2)}\text{A}\text{?}$, Pbam z=2. Ti and Ni are disordered on one equipoint.     

Self-propagating high temperature synthesis of Ni0.35Zn0.65Fe2O4 ferrite powders

The stoichiometric Ni_0.35Zn_0.65Fe₂O₄ ferrite powders were synthesized by SHS method. In the process of SHS, the effects of the molar ratio Fe/Fe₂O₃ in the starting mixture, oxygen pressure, grain size and relative density of the raw materials on combustion temperature, combustion wave velocity, phase composition and microstructure of the combustion products were investigated. X-ray diffraction, scanning electron microscope, TEM, vibrating sample magnetometry were used to characterize the microstructure and magnetic properties of the products. The results showed that as the molar ratio Fe/Fe₂O₃ increases, the combustion temperature and combustion wave velocity increased. The same results can be observed when the oxygen pressure increased from 0.1 to 0.9 MPa. The increase of grain size and relative density of raw materials resulted in the decrease of combustion temperature and combustion wave velocity. Compared with other methods, SHS process leads to ferrite powders with improved magnetic properties.     

Fine-grained multiferroic BaTiO3/(Ni0.5Zn0.5)Fe2O4 composite ceramics synthesized by novel powder-in-sol precursor hybrid processing route

Dense, homogeneous, and fine-grained multiferroic BaTiO₃/(Ni_0.5Zn_0.5)Fe₂O₄ composite ceramics are synthesized by a novel powder-in-sol precursor hybrid processing route. This route includes the dispersion of nanosized BaTiO₃ ferroelectric powders prepared via conventional sold-state ceramic process into (Ni_0.5Zn_0.5)Fe₂O₄ ferromagnetic sol-gel precursor prepared via sol-gel wet chemistry process. Uniformly distributed slurry is obtained after ball milling and used in the fabrication of the ceramics with low sintering temperatures. The ceramics show coexistence of ferromagnetic and ferroelectric phases with obvious ferromagnetic and ferroelectric hysteresis loops at room temperature, besides exhibiting excellent magnetic and dielectric properties in a wide range of frequency. The combination of high permeability and permittivity with low losses in the ceramics enables significant miniaturization of electronic devices based on the ceramics.     

Complex permeability and microwave absorbing properties of planar anisotropy carbonyl-iron/Ni0.5Zn0.5Fe2O4 composite in quasimicrowave band

Planar anisotropy carbonyl-iron (PACI)/Ni_0.5Zn_0.5Fe₂O₄ composite as absorbent filler in quasimicrowave band has been synthesized via ball-milling technique and solvothermal method. The effective permeability of the composite was measured and calculated. The result indicates that the magnetic loss in the composite is mainly caused by the natural resonance. Compared with the uncoated PACI particles, the permittivity of the composite decreased dramatically, and hence a dramatic enhancement of reflection loss (RL) was obtained in quasimicrowave band. This result indicates that our PACI/ferrite composite can be used as potential microwave absorbers in quasimicrowave band for its novel microwave properties.     

Nanocrystalline Ni0.8Zn0.2Fe2O4 films prepared by spray deposition from polyol-mediated sol: Microstructural and magnetic characterization

Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-based Ni_0.8Zn_0.2Fe₂O₄ sol on a moderately heated glass substrate. The microstructural and magnetic properties of these films are investigated by X-ray diffraction, scanning electron microscopy and magnetic measurements on a Super Quanducting Interference Devices magnetometer. They are compared with those of nanoparticles precipitated from the sol, and with those of film subsequently annealed in air at 400 °C. The films and the powder exhibit superparamagnetic behaviour with a blocking temperature which increases from the powder to the as-produced film to the annealed film, in agreement with increasing stress and/or crystal size. They are ferrimagnetic at low temperature with a hysteresis feature strongly dependent on the synthesis conditions. The stresses induced in the film upon deposition undoubtedly correlate with a large grain boundaries volume which contributes to the H_c, the coercitive field, increase and M_sat, the saturation magnetization, decrease.     

Deformation mechanisms of a bimodal eutectic Mg72Cu5Zn23 ultrafine composite

Deformation behavior of a Mg₇₂Cu₅Zn₂₃ alloy containing bimodal eutectic structure has been systematically investigated based on microstructural changes upon different amounts of compressive strain. The microstructural evolution of the sample at the early stage of the deformation up to 3% strain reveals that a large number of twins form homogeneously in the α-Mg phase of the coarse eutectic structure. After further deformation to failure, propagation of cracks takes place along the interface between the fine and coarse eutectic structures forming a typical dimple-like morphology on the fracture surface, indicative of the effective dissipation of the stress.     

Ba(Zn1/3Nb2/3)O3/Ni0.8Zn0.2Fe2O4 magneto-dielectric composite with large dielectric constant and high permeability

Ba(Zn_1/3Nb_2/3)O₃/Ni_0.8Zn_0.2Fe₂O₄ (BZN/NZO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using XRD and SEM, respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BZN/NZO composites have large dielectric constants and very high permeabilities. For the 20%BZN/80%NZO composite, the dielectric constant and permeability in low frequency range are about 8,000 and 18, respectively. The large dielectric behavior of the BZN/NZO composites is mainly attributed to the Maxwell–Wagner polarization.     

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.     

Ni53Mn21Fe1Ga25铁磁性形状记忆合金的显微组织和相变行为

主要研究了少量掺铁对NiMnGa铁磁性形状记忆合金的相变行为和显微组织的影响.透射电镜结果表明1%(原子分数)Fe元素的加入并不会改变基体NiMnGa合金的显微结构,母相仍为L21有序结构,马氏体为7M马氏体,其亚结构为孪晶.DSC结果表明在马氏体逆相变发生前存在一个预相变,这在NiM1nGa系合金中还是第一次发现.研究表明掺铁NiMnGa合金仍然具有良好的磁性能.     

Dielectric, elastic, anelastic and conductivity behaviour of ferroelectromagnetic composites, Ni0·5Zn0·5Fe1·95O4?δ + Ba0·8Pb0·2TiO3

Ferroelectromagnetic composites with compositions, X Ni_0·5Zn_0·5Fe_1·95O_4−δ + (1 − X) Ba_0·8Pb_0·2TiO₃, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.     

On the Ni5Al3 phase and related phenomena in a NiAlFe alloy

The Ni₅Al₃ Phase and related phenomena have been systematically studied using a Ni-25Al-15Fe alloy, with conventional and in situ optical microscopy and electrical resistance measurements. The present experimental results are comprehensively discussed in comparison with previous reports in order to clarify the complex characteristics of the Ni₅Al₃ phase and its formation mechanism.     

高温形状记忆合金Ni54Mn25Ga21相变及其形状记忆效应的研究

主要研究了马氏体相变温度Ms高于居里温度Tc的Ni54Mn25Ga21合金的相变及其单晶的形状记忆效应.采用真空电弧炉熔炼,然后用磁悬浮区熔晶体生长炉进行Ni54Mn25Ga21合金的单晶生长,成功制备了Ni54Mn25Ga21单晶.对多晶粉末样品进行了原位X射线衍射变温分析,结果表明Ni54Mn25Ga21合金具有可恢复的热弹性马氏体相变性能.对Ni54Mn25Ga21单晶进行的形状记忆效应实验结果表明,当总预应变不超过6%时,压缩变形后残留的应变可在随后的加热过程中完全回复.     

Fabrication of Ni2In3 alloy nanotubes

Alloy nanotubes were successfully grown by self-organization. They were produced by annealing of carbon-nickel-indium mixture thin films that were prepared by pulsed laser deposition. The morphology was observed and analysed by both scanning and transmission electron microscopes. The diameters were tens of nanometres and the aspect ratios were more than 2500. The growth is suggested to be due to the driving force that originated from supersaturation of alloying liquid indium with solid nickel.     

(Ni0.81Fe0.19)66Cr34缓冲层对Ni74Co26薄膜各向异性磁电阻的影响

用磁控溅射方法制备了以Ta和非磁性(Ni0.81Fe0.19)66Cr34为缓冲层的Ni74Co26薄膜,研究了它们的各向异性磁电阻效应.结果表明用厚度为4.5nm的非磁性(Ni0.81Fe0.19)66Cr34做缓冲层的Ni74Co26薄膜,其各向异性磁电阻(AMR)值比用10nm的Ta做缓冲层的同样厚度的Ni74Co26薄膜的AMR有较大的提高.比如,当Ni74Co26薄膜的厚度为12.5nm时,AMR值能提高43%.X射线衍射(XRD)研究表明缓冲层(Ni0.81Fe0.19)66Cr34与磁性层Ni74Co26有非常接近的晶格常数,因此产生了较大的AMR值.     

Cr13 Ni5Si2 /γ-Ni 三元金属硅化物高温耐磨复合材料

采用激光熔化/ 连续沉积工艺制备出以Cr₁₃Ni₅Si₂ 三元金属硅化物为初生相、以γ2Ni 基固溶体为连续增韧相(基体) 的三元金属硅化物耐磨复合材料(Cr₁₃Ni₅Si₂ /γ) 。在高温滑动磨损条件下测试了Cr₁₃Ni₅Si₂ /γ复合材料的耐磨性能随温度的变化规律, 并讨论了其磨损机理。结果表明, 由于Cr₁₃Ni₅Si₂ 三元金属硅化物具有原子结合力强和硬度2温度关系反常等特点, 且Cr₁₃Ni₅Si₂ /γ复合材料具有优良的强韧性配合, 以及Cr₁₃Ni₅Si₂ /γ复合材料在高温磨损过程中磨损表面能够形成转移覆盖层, Cr₁₃Ni₅Si₂ /γ材料在高温滑动磨损条件下具有非常优异的耐磨性能, 较低的磨损温度敏感性和反常的磨损2温度关系。韧性基体γ-Ni 的加入使Cr₁₃Ni₅Si₂ 三元金属硅化物在600 ℃高温下滑动耐磨性能提高了3 倍。     

Sol-gel synthesis and structural characterisation of binary TiO2-P2O5 glasses

An improved method for the sol-gel synthesis of binary (TiO₂)_0.5(P₂O₅)_0.5 glasses has been developed. Elemental analysis of the products showed that the loss of phosphorous upon drying and heat treatment is low. The structure of the heat-treated glasses was studied using neutron diffraction and high-energy X-ray diffraction, analysis of which revealed a structure consisting of PO₄ tetrahedra and TiO₆ octahedra sharing corners in a three-dimensional amorphous network. The Reverse Monte Carlo method was used to produce a structural model which illustrated that the structure of the glass is, at the near-neighbour level, closely analogous to the superstructure of crystalline TiP₂O₇. No significant atomic-scale structural differences were observed between glasses prepared by acid- or base-catalysed sol-gel reactions.     

Investigation of amorphous Ni0.60Nb0.40 diffusion barriers

Interactions of Ni_0.60Nb_0.40 amorphous alloys with polycrystalline overlayers of gold and copper and single-crystal substrates of silicon. GaAs and GaP were observed with Auger depth profiling. The Ni-Nb layer was deposited by r.f. sputtering and was approximately 5000 Å thick. The overlayers were evaporated to a thickness of 1000 Å. The amorphous metal reacted with the gold overlayers and the GaAs and GaP substrates at temperatures well below the nominal crystallization temperature of 650 °C. The Cu/Ni-Nb/Si system, in contrast, was stable at 600 °C for at least 1 h. Samples were also measured that had been contaminated with approximately 5–10 at.% O. Complete separation of the niobium and nickel into distinct layers was seen. For the samples on silicon substrates this separation was accompanied by the formation of a nickel silicide layer.