Magnetic properties of ternary RMn2Si2 and RMn2Ge2 compounds

Magnetic properties of RMn₂Si₂ and RMn₂Ge₂ compounds, where R is a rare earth metal, have been investigated by magnetometric measurements. RMn₂Ge₂ (where R is a light rare earth) and LaMn₂Si₂ are ferromagnets. Remaining compounds have antiferromagnetic properties. DyMn₂Si₂ and ErMn₂Si₂ show ferromagnetic properties at low temperatures. It was confirmed that the value of Curie (or Néel) temperature for the Mn sublattice decreases with increasing c constant.     

Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

The magnetic, transport and structural properties are studied for La_0.83Sr_0.17MnO₃ and La_0.82Sr_0.18CoO₃ single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т^?>T_C in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator–metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn³⁺ and Co³⁺ ions.     

Ab initio calculation of Zn0.8Mn0.2O1−yNy

Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), we investigated the magnetic and half-metallic properties of Mn-doped p-type ZnO and the mechanism which control these properties. Mn-doped ZnO is anti-ferromagnetic spin-glass state, but it becomes half-metallic ferromagnetic upon holes doping. The electronic structure, total magnetic moment of Zn_0.8Mn_0.2O_1−yN_y and magnetic moments of Mn and N in Zn_0.8Mn_0.2O_1−yN_y are calculated for different holes (y) concentrations. In this paper we address the origin of half-metallic and ferromagnetic properties as controlled and oriented by the nature of hybridization of the Mn (3d) state and host p(N) states. The band structure has been used to explain the strong ferromagnetism observed in Zn_0.8Mn_0.2O_0.1N_0.9.     

Effects of compositions on characteristics and microstructures for melt-spun ribbons and die-upset magnets of Nd12.8+xFe81.2−x−y−zCoyGazB6

The effects of varying Nd-contents on the magnetic properties of Nd_12.8+xFe_{81.2−x−y−z}Co_yGa_zB₆ ribbons and the resulting die-upset magnets have been investigated. It was found that the Nd content has a significant effect on both magnetic properties and texture of the die-upset magnets. An optimum Nd content exhibits good texture, while both Nd-lean and excessively Nd-rich Nd-Fe-B alloys lead to unsatisfactory textures. The magnetic properties and texture of the die-upset magnets strongly deteriorated with a further increase in the Nd-content. The thermo-mechanical characteristics and the formation mechanism of two kinds of cracks in backward-extruded ring magnets have also been investigated.     

Compositional dependence of the optical properties of the amorphous GexTe1−x system

Optical absorption at room temperature of vacuum evaporated Ge_xTe_1−x (0.125?x?0.225) amorphous thin films has been studied as a function of composition. It was found that the optical absorption is due to a direct transition. The real and imaginary parts of the dielectric constant were determined. The single-oscillator energy (E_o) and the energy dispersion parameter (E_d) have been calculated and discussed in terms of the Wemple and Di-Domenico model. The relationship between the optical gap, the average heat of atomization and the coordination numbers has been determined. The optical properties of the amorphous thin films do not change monotonically with increasing Ge content. The observed behavior of the optical properties in the range of compositions studied are explained on the basis of the Bond Constraint Theory (BCT) and rigidity theory, which provide a powerful framework for understanding the structure and properties of amorphous materials. The non-monotonic variation of the optical properties indicates that a transition from floppy to rigid occurs in the Ge_xTe_1−x films.     

Structural and mechanical properties of MoS2–Ix nanotubes and Mo6SxIy nanowires

Using a scanning probe microscope, we investigate the structure, electronic and mechanical properties of MoS₂–I_x nanotubes and Mo₆S_xI_y nanowires. The electronic properties are interestingly very sensitive to the stoichiometry of the nanowires, which can be controlled by adjusting the synthesis conditions. In addition to that, we find also remarkable mechanical properties where molecules can be cut and recombined or deformed without any loss of structural integrity. We demonstrate this by deforming Mo₆S_xI_y nanowires to highly strained configurations without causing irreversible changes to their structures. The rupturing and/or welding process of these nanowires, using AFM manipulation, shows that the molecules stretch to more than 30% of its relaxed configuration before plastic deformation occurs.     

Polarization characteristics of the relaxor ceramics of multicomponent system with PbNb2/3Zn1/3O3, PbNb2/3Mg1/3O3, and PbTiO3

The phenomenon of dielectric hysteresis in the relaxor ceramics of multicomponent system with PbNb_2/3Zn1/₃O₃, PbNb_2/3Mg_1/3O₃, PbTiO₃ has been studied. The influence of different modifiers on polarization characteristics is examined and the correlations of these properties with the phase and chemical composition of the ceramics are investigated. The results obtained can be used to predict relaxor properties.     

Hard magnetic properties of melt-spun Co82Zr18−xTix alloys

The phases and magnetic properties of Co-Zr-Ti melt-spun ribbons were studied by XRD analysis and magnetic measurements. The optimal magnetic properties of Ms=59.0 emu/g, Mr=4.0 kG, Hc=2.9 kOe, and (BH)_max=3.0 MGOe were obtained in Co₈₂Zr₁₄Ti₄ ribbons produced at a wheel speed of 30 m/s. In this work, we found that Ti was one of the few large atomic radius elements, which could improve hard magnetic properties of Co-Zr alloy.     

Magnetic and transport properties in Sr1−xLaxFe1−xMnxO3

The magnetic and transport properties in the perovskite Sr_1−xLa_xFe_1−xMn_xO₃ have been explored. As x rises, the systemic ferromagnetism increases gradually and cluster-spin-glass state occurs in the low-temperature region. For 0.3?x?0.7, the ferromagnetic phase separation from the paramagnetic phase was observed from the results of electron-spin-resonance measurement. Although all samples show a semiconducting behavior, their transport properties are dominated by two different mechanisms, namely, the electronic transport of x?0.5 samples is realized by thermal activation but the variable-range hopping is applied in x?0.7 ones. The different transport mechanism can be understood from the Mn/Fe ions interaction.     

Characterization of the magnetic properties of a GdBa2Cu3O7/La0.75Sr0.25MnO3 superlattice using off-axis electron holography

Off-axis electron holography is used to characterize the magnetic properties of a GdBa₂Cu₃O₇/La_0.75Sr_0.25MnO₃ superlattice below the Curie temperature of the manganite layers, in both cross-sectional and plan-view geometry. The samples were prepared for electron microscopy using focused ion beam milling. Differences between the magnetic properties of successive manganite layers are observed in the cross-sectional sample. Magnetic ripple contrast and weakly magnetic regions are observed in plan-view geometry. Although the results may be affected by sample preparation for electron microscopy, the observed differences between the magnetic properties of the manganite layers are consistent between the different samples examined.     

非化学计量和掺杂对(Na1/2Bi1/2)0.92Ba0.08TiO3陶瓷电性能的影响

研究了非化学计量和掺杂对无铅压电陶瓷(Na_1/2Bi_1/2)_0.92Ba_0.08TiO₃的压电性能及去极化温度的影响.研究发现A位非化学计量可以提高陶瓷的压电性能;B位掺杂对材料电学性能的影响规律类似于Pb(Ti,Zr)O₃系压电陶瓷的相关规律;由于非化学计量和掺杂会影响到A位离子对B位离子与氧离子形成的BO₆八面体的耦合作用,影响到畴的稳定性,从而影响 关键词： 无铅压电陶瓷 非化学计量 掺杂 电性能     

Preparation and characterization of Y1−xPrxBa2Cu3O7−δ single crystals

We present a reliable method for growing single crystals of Y_1−xPr_xBa₂Cu₃O_7−δ high-T_c superconductors in ZrO₂ crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al₂O₃ crucibles. We describe techniques for crystal growth in both Al₂O₃ and ZrO₂ crucibles using an excess of BaCo₃ and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant.     

Fe65B22Nd9Mo4 bulk nanocomposite permanent magnets produced by crystallizing amorphous precursors

The Fe₆₅B₂₂Nd₉Mo₄ nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe₆₅B₂₂Nd₉Mo₄ alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence (B_r) of 0.56 T, coercivity (_iH_c) of 920.7 kA/m and maximum energy product (BH)_max of 50.15 kJ/m³ were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe₆₅B₂₂Nd₉Mo₄ magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe₃B and hard Nd₂Fe₁₄B magnetic grains.     

Si基Bi3.25La0.75Ti3O12铁电薄膜的制备与特性研究

采用Sol-Gel工艺低温制备了Si基Bi_3.25La_0.75Ti₃O₁₂铁电薄膜.研究了退火温度对薄膜微观结构、介电特性与铁电性能的影响.500℃退火处理的Bi_3.25La_0.75Ti₃O₁₂薄膜未能充分晶化，晶粒细小且有非晶团聚，介电与铁电性能均较差.高于550℃退火处理的Bi_3.25La_{0.75 关键词： 铁电薄膜 3.25}La_0.75Ti₃O₁₂')" href="#">Bi_3.25La_0.75Ti₃O₁₂ Sol-Gel工艺     

Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75): A first-principles study

The structural, elastic, electronic and optical (x=0) properties of doped Sn_1−xBi_xO₂ and Sn_1−xTa_xO₂ (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants C_ij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO₂ in two polarization directions are compared with both previous calculations and measurements.     

First-principles study of single-walled armchair Cx(BN)y nanotubes

The structural and electronic properties of the armchair C_x(BN)_y nanotubes are studied using the density functional theory with a generalized gradient approximation. The results show that the properties of the C_x(BN)_y nanotubes are intermediate between those of carbon nanotubes and BN nanotubes, and also adjustable by their radius, ratio of carbon component, and configurations.     

Structure, magnetic and superconducting properties of MoSr2HoCu2O8−δ

Samples with nominal composition MoSr₂HoCu₂O_8−δ were synthesized and their magnetic and superconducting (SC) properties were investigated. The obtained samples are Mo-deficient. It was established that the magnetic order is of a long-range type. The coincidence of the experimental value of the Curie constant and the theoretical one of MoSr₂HoCu₂O_8−δ shows that the observed magnetic properties of the samples are determined by the highly dominating phase Mo-1212. The two-step resistive SC transition, together with the absence of both diamagnetism and a peak in the specific heat between the two critical temperatures may be associated with the presence of a granular superconductivity. The effect of the Mo-deficiency on the magnetic and SC properties of MoSr₂HoCu₂O_8−δ was discussed.     

p型BayFexCo4-xSb12化合物的热电性能

以2+价的Ba作为填充原子,在x=1.0—1.6,y=0—0.63的组成范围内,系统地研究了Ba填充分数及Fe含量对p型Ba_yFe_xCo_4-xSb₁₂化合物电性能及热性能的影响,探讨了填充原子的氧化价对电性能的影响规律,优化了p型Ba_yFe_xCo_4-xSb₁₂化合物的组成和热电性能,对于富Co组成的Ba_0.27FeCo₃Sb₁₂试样,本研究得到了0.9最大无量纲热电性能指数(ZT). 关键词： 填充分数 载流子浓度 电导率 赛贝克系数 晶格热导率     

FexNi100−x nanometric films deposited by laser ablation on SiO2/Si substrates

Fe_xNi_100−x nanometric films were deposited on SiO₂/Si substrates at room temperature using the pulsed laser deposition technique. The targets were Fe-Ni amorphous magnetic foils with composition Fe₅₀Ni₅₀, Fe₃₅Ni₆₅ and Fe₂₂Ni₇₈. Morphological and structural properties of the deposited films were investigated using scanning electron microscopy, Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and X-ray reflectivity. Electrical and magnetic characteristics of the films were investigated by using the four-point probe and the magneto-optic Kerr effect techniques, respectively. The film properties are strictly dependent on the Fe-Ni compositional ratio.     

Magnetic and magneto-transport properties of double perovskite Ba2−xSrxFeMoO6 system

The structural magnetic and magneto-transport properties of double perovskite system Ba_2−xSr_xFeMoO₆ (0?x?1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe-Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba₂FeMoO₆ exhibits saturation magnetic moment value of 3.54 μ_B/f.u. at 85 K in a magnetic field of 6000 Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73 μ_B/f.u. and MR value of 7.08% (1 T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail.