Magnetic-field tuning of the alloy-induced disorder in quaternary semimagnetic (Zn, Cd, Mn)Se quantum well structures

The influence of magnetic-field-induced tuning of the disorder on the line width of the lowest excitonic transition in diluted magnetic semiconductor (Zn, Cd, Mn)Se/ZnSe quantum well samples is studied by photoluminescence at 2 K and in magnetic fields up to 7.5 T. It is shown that the dependence of the photoluminescence line width on quantum well thickness can be explained as a sum of contributions of ZnSe barrier, (Zn, Cd, Mn)Se well and the interfaces.     

Ferromagnetic superconductors: Effect of disorder on the coexistence phase in ErRh4B4 and pseudoternary systems

The asperomagnetic ordering model with a randomly oriented easy axis in the basal plane provides a natural explanation of the unusual magnetic properties of ErRh₄B₄, including the different results of Mössbauer and neutron diffraction measurements of the magnetic moment in the normal low temperature magnetic phase (FN phase) as well as anomalies in the magnetic ordering at the transition from the nonmagnetic superconducting phase (S phase) to the FN phase. Here the small intensities of satellites and the simultaneous appearance of ferromagnetic peaks and satellites are explained in terms of the destruction of inhomogeneous magnetic structure in the coexistence phase due to disorder in the main part of the sample. The effect of disorder on the coexistence state in pseudoternary compounds is also considered.     

Anomalous magnetic susceptibility and inhomogeneous magnetic state in lanthanum strontium manganites

Anomalous magnetic susceptibility χ has been observed in mono-and polycrystalline (ceramic) samples of lanthanum strontium manganites. The oscillations of χ observed for single crystal samples in the vicinity of the Curie temperature (and in the paramagnetic region) are explained by the existence of magnetic clusters. The appearance of susceptibility oscillations in ceramic samples is attributed to the formation of magnetic clusters, which may occur both in grains (at the interface between ferro-and antiferromagnetic phases) and at the grain boundaries.     

Effect of chemical treatment on the magnetic properties of thin-film ferromagnetic systems

The effect of chemical treatments on the surface morphology and local magnetic characteristics of thin films of a FeN alloy and thin-film structures comprising submicron layers of this alloy separated by a silicon dioxide interlayer has been studied by microscopic and magnetooptical techniques. It is established that chemical etching in the presence of a magnetic field strongly changes both the surface morphology and magnetic properties of samples. The local values of the saturation field and coercive force in thin-film structures upon the chemical treatment are significantly different, which is related to the appearance of inhomogeneities on the sample surface and the resulting increased influence of stray fields on the measured magnetic characteristics.     

ECAP制备半硬磁2J4合金的磁性能研究

开发了用等径弯曲通道变形(ECAP)制备半硬磁2J4合金.研究结果表明:2J4合金的磁性能随着ECAP变形道次的增加而逐渐增大,在第3道次变形时,其磁性能增加速度最快.ECAP变形与冷轧类似,都形成极其相似的带状织构,提高了合金的各向异性常数.由于ECAP方式使晶粒细化,达到或接近单畴结构,使得2J4合金的磁性能优于冷轧条件下的磁性能.     

The reflectivity discrepancy method for the determination of thepermittivity and permeability of complex materials

The possibility of distinguishing whether the losses in a material under investigation are due to either its dielectric or magnetic properties, or both, is tested by treating a single spectrum of a reflection simulated by computer. To determine the frequency bandwidth and range of sample thickness sufficient to measure both the permittivity and the permeability at any frequency, the reflection spectrum of a sample with magnetic and dielectric properties is analyzed. If the reflectivity is measured over a frequency band several times wider than the absorption line of the sample and the sample is semitransparent in the middle of the line, the magnetic and dielectric spectra may be determined. Insertion of an air gap between the sample, and the plane of the short circuit has been found to facilitate the measurements. The validity of this approach is shown with permittivity and permeability measurements of a composite substance containing iron     

Ultrasonic fatigue of nickel-chromium alloys at low temperatures

The influence of low temperature ultrasonic deformation on the electrical resistivity and magnetic properties of nickel-chromium dilute solid solutions is examined. It is shown that changes in the electrical resistivity and magnetic properties of prequenched samples after ultrasonic fatigue can be explained by order-disorder processes during fatigue. It is concluded that ordering at low temperatures during the ultrasonic deformation is associated with high strain rate and high vacancy concentration produced by deformation.     

The Influence of the Morphology on the Magnetic Properties of Poly(3-hexylthiophene)

The influence of the morphology on the magnetic properties of poly(3-hexylthiophene) has been studied and the results reported. The changes in the saturation magnetization were explained considering the polymer morphology prepared with different amounts of water in the solution during sample synthesis. The results show that the saturation magnetization is maximized for 200 ppm of the water in acetonitrile solution.     

Effect of Grain Size on Magnetic Properties of ZnO Doped with Nickel Single Impurities

The purpose of our study is to find a suitable material to be used in spintronic applications and to find the relation between the parameters of deposition by spray pyrolysis technic (temperature, concentration of Ni doping) and the ferromagnetic properties (Curie temperature, magnetic moment). The nickel-doped zinc oxide, Zn.1?x.NixO (x = 0.01, 0.03, 0.05), and diluted magnetic semiconductors (DMSs) are synthesized by the spray pyrolysis technic. The results of The X-ray diffraction (XRD) of prepared substrates confirm the incorporation of the dopants into the ZnO lattice structure. The spin-polarized electronic properties has been found and was investigated in detail by using the density-functional theory (DFT), the local density approximation (LDA), and The Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA). As result, nickel doping brings up a half-metallic appearance due to the hybridization between the 3d state of Nickel impurities and the oxygen 2p state. The mechanism of the interatomic exchange has been explained as being a p-d double exchange.     

Effect of cycling on the magnetization of ion exchanged magnetic nanocomposite based on polystyrene

Magnetic nanocomposites containing iron oxide particles embedded in a polymer matrix have been synthesized using the method of ion exchange. They have been characterized by using low temperature and room temperature magnetic measurements and Mössbauer spectroscopy. The iron content in these samples has also been determined. The results have been analysed and explained. The physical and chemical properties of these nanocomposite materials are different from those of the bulk. Some of the unique properties of these materials find application in information storage, color imaging, ferrofluids and magnetic refrigeration.     

Local magnetic properties of a monolayer of Mn12 single molecule magnets

The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled beta-detected nuclear magnetic resonance. A low-energy beam of spin-polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance line width varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the line width indicates that the magnetic properties of the Mn12 moments in this low-dimensional configuration differ from bulk Mn12.     

The effect of heat-treatment in a magnetic field or under an applied stress on the magnetic properties of silicon-iron

The effects of heat-treatment in a magnetic field or under an applied stress have been studied in this investigation. Magnetic properties (magnetostriction and power loss in particular), measured along the rolling direction in grain-oriented silicon-iron were unaffected by magnetic annealing, but their stress-sensitivities were improved by annealing under tension.Magnetic annealing was found to be effective in non-oriented silicon-iron and also in grain-oriented material if it was annealed with the field applied along directions other than the rolling direction.The magnetic annealing results can be explained largely on the basis of the Néel-Taniguchi theory of directional ordering of atom pairs. The changes obtained by annealing under stress showed that directional order only plays a minor part. The magnetic changes could be explained by assuming that during heat-treatment under stress a process of magnetostriction strain relief occurs, forming a residual internal stress.Other alloys similar to silicon-iron showed no more response to magnetic annealing or annealing under stress than silicon-iron.     

The Hysteresis Behavior of a Spin-1 Blume-Capel Nanoisland

The magnetic properties of a spin-1 Blume-Capel nanoisland are investigated by the use of the effective field theory based on the probability distribution technique. The influence of the random crystal field and the system parameters on the hysteresis behavior and on the magnetic properties of the nanoisland is examined. The results show a number of characteristic behaviors, such as the appearance of double, triple, quadruple, and even quintuple hysteresis loops for appropriate values of the system parameters.     

Features of the magnetic properties of Co/Si/Co thin-film systems

The magnetic properties of Co/Si/Co thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. It is established that the saturation field (H _S) of trilayers exhibits oscillations as a function of the thickness of the semiconductor (silicon) interlayer. This behavior is explained by structural features of the Co/Si/Co system and the presence of antiferromagnetic exchange coupling between magnetic layers via the silicon interlayer.     

Magnetically induced nonlinear diagnostic features of fe-co-si-B metallic glasses

We investigate the influence of an external magnetic field on optical photoinduced second-harmonic generation (PISHG) in Fe(18)Co(60)Si(9)B(13) metallic glass. A correlation between the output PISHG signal and degree of crystallinity (varied by thermoannealing) is observed. The applied magnetic field essentially suppresses the relaxation time of the PISHG. Strong angular dependence of the output PISHG signal reflects the peculiarities of phase synchronism conditions that exist in certain types of glass as a result of light scattering on grains. Saturation of the PISHG at magnetic fields higher then 0.75 T indicates correlation between the magnetically induced ordering and noncentrosymmetry electron-charge density appearance. Comparison of PISHG with x-ray diffraction results indicates that the PISHG results have higher sensitivity to hyperfine magnetic ordering. A possible origin of the observed phenomena is explained on the basis of phenomenological and microscopic approaches.     

Improvement of the foaming process for 4045 and 6061 aluminium foams by using the Taguchi methodology

Taguchi methodology has been applied to the production process of aluminium foams to investigate the variability detected in several properties (including bulk density, outward appearance and density homogeneity along foaming direction), for foaming tests carried out under identical conditions. The analysis of the process has been performed separately for two different alloys, the 4045 and 6061. The results have allowed finding the main factors that influence those properties. In addition, it has been possible to establish those foaming conditions able to minimize the variability in density, to improve the outward appearance and to obtain a higher homogeneity in density, all at the same time. Different final factors have been found for the two alloys; such differences have been explained in terms of the different viscosity of the aluminium melts as well as the different content of foaming agent.     

Influence of annealing and rinsing on magnetic and photocatalytic properties of TiO2

Samples of TiO₂, calcined at 100 °C (type 1) and 200 °C (type 2), have been prepared without and with water rinsing. The crystallite sizes determined by XRD method were smaller than 15 nm for both types of samples. Magnetic resonance spectra of the obtained samples have been studied in 230-300 K temperature range. Before rinsing no magnetic spectra were observed but after rinsing the magnetic response appeared in form of a resonance line centered at g_eff ∼ 2.54 with linewidth ΔH_pp ∼ 460 G in type 1 samples and g_eff ∼ 2.26 with linewidth ΔH_pp ∼ 220 G in type 2 samples. The integrated intensity of the observed spectrum was two times greater in the type 1 sample. The resonance line could be attributed to the localized magnetic moments in the correlated spin system formed during rinsing. The rinsing resulted also in higher photocatalytic properties under UV-VIS irradiation. It is suggested that the number of oxygen vacancies increases after rinsing and as they are involved in the formation of low oxidation states of titanium ions, they could be responsible for the appearance of the observed magnetic properties.     

钢管漏磁在线检测技术的研究

介绍了钢管漏磁检测的基本原理，对钢管在线漏磁检测系统进行总体设计。分析了漏磁场理论模型和讨论了影响缺陷漏磁信号的一些因素及补偿方法，针对该系统的特点设计了高速数据采集板，借助Windows系统平台，在所研制硬件的基础上，采用多线编程和虚拟设备驱动技术编制了数据采集、分析、状态显示、实时控制等面向对象、多功能模块化的软件，详细叙述了漏磁信号数据分析的方法和过程。这种系统具有检测速度快、数据吞吐量大、效率高、钢管缺陷分辨率高等特点。     

纳米级FePt/Fe多层膜中微结构的优化与耦合效应

本文用磁控溅射法制备了一系列不同厚度Fe层的FePt/Fe多层膜,经过热处理后成功地制备出具有fct结构的FePt有序相和exchange-spring型永磁体.研究了不同热处理条件下多种膜层厚度与FePt/Fe多层膜结构、磁性及其内在关系,并探讨了FePt/Fe多层膜铁中的磁耦合失效问题.观察了不同热处理条件和层厚的FePt/Fe多层膜的结构变化过程,包括结构相变、有序度和晶粒度.研究了其磁性能随结构变化的规律,发现了耦合失效的模式.     

Effects of annealing on the magnetic properties and microstructure of Fe-ZrN nanocomposite films

We have studied the influence of thermal annealing on the magnetic properties and microstructure of 0.7-μm-thick Fe-ZrN nanocomposite films obtained by a reactive RF magnetron sputtering technique on non-conductive substrates. The near-surface and bulk magnetostatic characteristics of the films were studied using magnetooptical and vibrating-sample magnetometers, respectively. The microstructure was determined by X-ray diffraction. It was established that the magnetic characteristics strongly depend on the annealing temperature. These dependences are explained by structural changes induced in the films by the thermal treatment.