钢轨纵向应力和巴克豪森效应的关系

铁磁材料在磁化场作用下磁畴的不可逆运动产生巴克豪森效应，此效应依赖于材料的显微组织和应力状态，可做为无损检测铁磁材料内应力的一种新方法，本文从实用性出发探讨了钢轨材料的巴克豪森特征及钢轨纵向应力和巴克豪森效应的关系，做为检测钢轨温度纵向应力的实验基础。     

Improved coercivity of W- and M-type composite hexaferrites using two different synthesis routes

Two series of W- and M-type composite hexaferrites were synthetized using the conventional ceramic method in two different synthesis routes. In the first synthesis route, W- and M-type composite hexaferrites were formed by reaction in the pre-sintering stage. In the second synthesis route, W- and M-type composite hexaferrites were obtained by physically mixing W- and M-type hexaferrites in the second ball milling stage. The influence of M-type phase on the structure and magnetic properties of W-type hexaferrites synthesized in both synthesis routes are investigated in detail. For both synthesis routes, X-ray diffraction (XRD) patterns of all samples indicated crystallization of W- and M-type hexaferrites phase and scanning electron microscopy (SEM) measurements revealed hexagonal platelet-like grains. In the pre-sintering stage, the saturation magnetization (4πM_s) of all samples ranged between 3.30 kG and 4.25 kG. The remanence ratio (M_r/M_s) changed from 0.77 to 0.88 with the increase of pre-sintering temperature. The coercivity (H_c) of all samples ranged between 456 Oe and 1846 Oe. The ferromagnetic resonance (FMR) linewidth (ΔH) ranged between 466 Oe and 748 Oe. In the second ball milling stage, 4πM_s and M_r/M_s maintained a relatively stable value of ~4.5 kG and ~0.89, respectively. H_c increased from 519 Oe to 620 Oe with the increase of M-type hexaferrites. ΔH ranged between 317 Oe and 573 Oe. We note that in both synthesis routes only the composite hexaferrites synthesized in the pre-sintering stage have a significantly improved coercivity from 456 Oe to 1846 Oe. This enhancement in coercivity is attributed mainly to the effect of exchange coupling among ferrite grains. In addition, the ΔH decreases with the addition of M-type hexaferrites.     

Fe–Co co-doping effects on antiferromagnetic core of NiO nanoparticles

The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M ? H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.     

Elastically stressed state at the interface in the layered ferromagnetic / ferroelectric structures with magnetoelectric effect

This article shows that in layered structures representing thin (～2 μm) cobalt, nickel and permendur layers on ferroelectric ceramics substrates (～400 μm) the elastic strains at the interface make a more significant contribution to the magnetoelectric effect than the ferromagnetic layer magnetostriction. For obtaining these structures the ion-beam sputtering – deposition after ion-beam planarization of the substrate surface was used. The magnetoelectric voltage coefficient at a frequency of an alternating magnetic field of 1 kHz at room temperature for structures with cobalt is higher than that for structures with nickel and permendur. The structures obtained are thermostable within the temperature range from ?25 to +120 °C and have reproducible magnetoelectric properties. These structures can find their application as magnetoelectric converters and magnetic fields sensors.     

Electrodeposition of CoMoP thin film as diffusion barrier layer for ULSI applications

CoMoP thin films were fabricated by electrodeposition technique from citrate based bath onto Cu sheets for the application as diffusion barriers and metal capping layers in the copper interconnect technology. The study focused on the effect of (NH₄)₆Mo₇O₂₄·4H₂O concentrations in the plating solution on the plating rate and chemical composition of the deposited layer. It was found that the Mo wt.% in the deposited layer increased from 13 to 22 wt.% with increasing (NH₄)₆Mo₇O₂₄·4H₂O concentration. The influence of deposition current density, solution pH and deposition temperature at certain (NH₄)₆Mo₇O₂₄·4H₂O concentration in the plating bath on the plating rate and chemical composition was studied. Polarization behavior of induced co-deposition of CoMoP at various electrolyte pH values was studied using cyclic voltammetry and chronoamperometry to estimate the current efficiency (CE%) of the plating solutions and the optimum pH for the plating process. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques have been applied to characterize the morphology and chemical composition of the deposited layer. CoMoP alloys of high P wt.% as-deposited films showed irregular microcracks amorphous structure and of low P wt.% showed amorphous/nanocrystalline structure while, after annealing at 400 °C for 1 h, the films deposited with low and high P wt.% converted into polycrystalline structure. The results of oxidation property showed that, the Co-13.2 wt.% Mo-10.3 wt.% P alloy has highest stability against oxidation and lowest electrical resistance values (100-150 µΩ). The ferromagnetism nature of coated materials has been studied by hysteresis loop measurements. The electrochemical corrosion results were calculated from polarization studies for as-plated and annealed CoMoP coatings in 3.5% NaCl solution.     

Microstructure and soft-magnetic properties of FeCoPCCu nanocrystalline alloys

Fe_83.2-xCo_xP₁₀C₆Cu_0.8 (x = 0, 4, 6, 8 and 10) alloys with a high amorphous-forming ability and good soft-magnetic properties were successfully synthesized. Saturation magnetic flux density (B_s) is effectively enhanced from 1.53 T to 1.61 T for as-quenched alloy by minor Co addition, which is consistent well with the result of the linear relationship between average magnetic moment and magnetic valence. For Co-contained alloys, the value of corecivity (H_c) is mainly determined by magneto-crystalline anisotropy, while effective permeability (μ_e) is dominated by grain size and average saturation polarization. After proper heat treatment, the Fe_79.2Co₄P₁₀C₆Cu_0.8 nanocrystalline alloy exhibited excellent soft-magnetic properties including a high B_s of 1.8 T, a low H_c of 6.6 A/m and a high μ_e of 15,510, which is closely related to the high volume fraction of α-(Fe, Co) grains and refined uniform nanocrystalline microstructure.     

受扭轴类零件磁记忆信号的初步研究

金属磁记忆检测技术是通过测试构件在外载荷作用过程中形成的表面微弱磁场的变化来监测其损伤状态的。利用该技术，研究了受扭磁性轴类构件的磁记忆检测信号特征，并探讨了磁场环境对构件在扭矩作用下磁记忆信号的影响。结果表明，磁记忆检测信号与构件的损伤状态之间具有明显的相关性，磁场环境对改善金属磁记忆检测效果具有较好的作用。     

纳米晶Fe_（73．5）Cu_1Nb_3Si_（13．5）B_9合金中缺陷及内应力的分布研究

用正电子湮没技术和微观磁学方法研究了纳米晶Ｆｅ_（７３．５）Ｃｕ_（１）Ｎｂ_（３）Ｓｉ_（１３．３）Ｂ_９合金结构缺陷在退火过程中的变化规律，表明晶化初期形成的界面结构只引入少量的缺陷，晶化后期由于出现大量晶界，缺陷浓度急剧上升；非晶制备过程中以及晶化时引入的准位错偶极子造成的应力场对其软磁性能有很大的影响，并可以解释在最佳退火温度的磁性行为。     

Effect of electron density on the martensitic transition in Ni-Mn-Sn alloys

The structure and martensitic transition (MT) temperatures of Ni₄₄Mn₄₅Sn₁₀R (R = Al, Ga, In and Sn) alloys were investigated. Valence electron concentration and cell volume are two main factors affecting the MT temperatures in Ni-Mn based Heusler alloys. Our results indicated that the MT temperatures do not vary monotonously with either of the two factors, but increase with the increasing of electron density. Combining the two factors, electron density might be a more appropriate parameter to describe the variations of MT temperatures.     

Numerical study of geometrical frustration: From square to triangular lattices

In this work we study the effects of geometrical frustration in square lattice which can be measured by the diagonal hopping integral. In the framework of the Hubbard model, we use quantum Monte Carlo method to calculate spin susceptibility and focus on magnetic fluctuations in this system. We find that in two filling regions, the effects of geometrical frustration are quite different. As a measure of geometrical frustration between square and triangular lattices, the diagonal hopping suppresses the anti-ferromagnetic fluctuation at half filling and enhances ferromagnetic fluctuation at 1.5 filling.