Non-collinear magnetism and exchange couplings in FeCo/Mn superlattices

We present the main results of a systematic study of the magnetic properties of Fe_xCo_{1 − x}/Mn_n for various Fe concentrations x and Mn thicknesses n. We show that the magnetic order in the Mn spacer changes from collinear to non-collinear when the Fe concentration decreases. This behaviour is discussed in relation with a bulk ‘canted’ magnetic state nearly degenerate with the collinear AF order. The origin of the exchange of stability between these two magnetic states is ascribed to a stronger collinear character of the Fe/Mn interface than the Co/Mn one.     

Interface defects and formation of non-collinear magnetic ordering in Fe/Cr multilayers

Non-collinear magnetic structure of Fe/Cr multilayers was investigated within the framework of Periodic Anderson model (PAM) in mean field approximation for Coulomb repulsion on sites. Self-consistent calculations were performed for the superlattices with different step width at the interface. It is shown that due to frustration in the interface region the ground state corresponds to non-collinear orientation of magnetic moments near steps. This non-collinear ordering penetrates on a large distance from the interface both in Fe and Cr layers and leads to the non-collinear magnetic coupling between Fe layers through the Cr spacer. Angle between magnetic moments of Fe slabs depends strongly not only on the thickness of the Cr spacer but also on the interface structure at atomic scale. It is found that only very specific types of the interface defects with plural frustrations can give out-of-plane orientation of magnetic moments.     

Determination of magnetic moment vectors distributions in FeCo/Mn superlattices

We present in details a method for determining non-collinear orders in metallic superlattices and the interlayer magnetic couplings between ferromagnetic layers separated by antiferromagnetic spacers. A semiempirical tight binding framework and the real space recursion technique is used to obtain the electronic structure of non-symmetric systems. We focus on the angular self-consistency and we discuss the angular stability of the solutions obtained by fixing the magnetic moment direction of some atoms. We give a few examples of calculations for bulk Mn and FeCo/Mn superlattices and discuss the validity of the results.     

Complex magnetic behavior at the surface of B2 ordered FeCr alloy

Bouzar et al. (1997) have recently investigated the surface of B2 FeCr alloy. In all cases of crystal growth 0 0 1, 1 1 0 and 1 1 1 they found the local polarization at the surface to be antiferromagnetically coupled with the subsurface layer in contrast to parallel coupling between Fe and Cr in bulk FeCr. In order to assert these results, we have investigated the local polarization of Fe at the (0 0 1) surface of this alloy with a tight-binding linear muffin tin Orbitals (TB-LMTO) model. Using general gradient approximation with Langreth-Mehl-Hu functional for p(1 × 1) and c(2 × 2) configurations we found the local polarization at the Fe surface layer to be antiferromagnetically coupled with the subsurface Cr layer and high magnetic moments compared to the bulk values.     

Theoretical foundation of cluster formation in supported liquid-phase catalysts

Despite the widespread use of supported liquid phase catalysts (SLPC) in industrial practice, the basic phenomenon of liquid dispersion which affects the diffusion rates of reaching components and gas-liquid interfacial area, is not well understood. The paper identifies the associated problems and formulates a model for the pore structure of real catalysts based on intersecting cylinders to study the effects of capillary forces. The formation of liquid clusters of dimensions larger than the pore dimensions and their subsequent effects on the performance of SLPC can be studied using this model. The model provides a basis for manipulating parameters that can reduce such cluster formation. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday.     

Influence of structure on the thermophysical characteristics of porous metals

An experimental investigation of the thermal conductivity and thermal diffusivity of porous copper and iron with different porous structures is made. A dependence of the thermophysical characteristics on the degree of porosity and the mean pore size is established. A correlation with the structural model made it possible to take into account the dependence of the pore size distribution on the parameters.Notation , _com thermal conductivity coefficients of porous and compact materials - ₁, ₂ thermal conductivity coefficients for the cases of isolated and intercommunicating pores - ₁ ^* , ₂ ^* thermal conductivity coefficients of monodisperse structures - a,a _com thermal diffusivity coefficients of porous and compact materials - C _p specific heat - density - P porosity - r, size and mean size of pores - r _str structural parameter - D variance of pore size - R size of an elementary cell - F(r, ,D) differential function of pore size distribution Altai State University, Barnaul. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 5, pp. 720–723, September–October, 1995.     

Evidence of hexagonal WO3 structure stabilization on mica substrate

WO₃ nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO₃ hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO₃ hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.     

Modeling of the surface treatment of passive metals

On the basis of analysis of the specific features of physicochemical reactions leading to the local destruction of the surface of passive metals, we conclude that it is impossible to construct an adequate kinetic model of its evolution. For modeling the processes of formation of the surface of metals inclined to passivation, we propose to use the formalization of discrete states with subsequent analysis of the dynamics of these processes. We have constructed a simulation model of the transformation of the morphology of an electrochemically active surface under the action of polarization by pulse current and proposed a scheme of the corresponding technological process and a quantitative criterion for the completion of treatment. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 69–75, January–February, 2008.     

Application of infra-red surface electromagnetic waves on metals in nondestructive surface testing

The elementary theory of surface electromagnetic waves (SEW), based on a local relation between the induced current density and electric field, is discussed. Based on this theory, typical values of propagation lengths and penetration depths are calculated in the infra-red and visible regions. Experiments using a double-prism configuration have been performed to demonstrate the relative coupling efficiency as a function of prism-gap height and angle of incidence, respectively, for infra-red SEWs. Approximate calculations of propagation lengths for infra-red SEWs on rough surfaces are presented.     

Periodic Anderson model for the description of noncollinear magnetic structure in low-dimensional 3d-systems

Distribution of magnetic moments in the low-dimensional metallic structures has been studied theoretically on the basis of periodic Anderson model. Calculation of noncollinear magnetic order was performed in the Hartree-Fock approximation using tight binding real space recursion method. Iteration process includes self-consistent determination of population numbers for the electrons with different directions of the magnetic moments at given atom relatively to the fixed axis. Energies of all states corresponding to the different directions of magnetic moments at the atom under consideration have been calculated, and the state with minimal energy being accepted for the next step.

Analytical transformations based on the generalised “zeros and poles method” were performed for the Green function that allows to avoid some time-consuming numerical procedures. It gives the possibility to develop efficient algorithm for the calculation of noncollinear magnetic structure of complex space nonhomogeneous systems.

Calculations performed for the parameters corresponding to Fe and Cr show the qualitatively different dependencies of the magnetic moment magnitude and the energies of d-electrons on the angles, which define the direction of magnetic moments.     

316L不锈钢表面沉积Pd／Fe磁性薄膜的研究

采用真空电弧离子镀技术在316L不锈钢表面沉积Pd／Fe薄膜，通过XRD衍射、SEM电镜及EDS分析了薄膜的组织结构、磁性能及电化学行为。结果显示：沉积态Pd／Fe薄膜经过500℃×15min真空扩散热处理后，薄膜由无序的fcc结构相转变成具有铁磁性的L10型fct结构的有序Pd／Fe舍金相，表面光滑均匀且致密，结合强度高，充磁后表面剩磁值达到12Gs，并且提高了材料的耐腐蚀性能。     

金属间化合物YFe12-xMx（M=V,Cr）的结构和磁性研究

采用线性缀加平面波展式结合改进的局域轨道方法(APW+lo),基于密度泛函理论(DFT),优化、计算和分析了Y、Fe、V、Cr和YFe12-xMx(M=V、Cr;x=0～5)体系的结构和能量。系统的总磁矩和原子磁矩的计算表明,YFe12-xMx的磁矩主要来源于Fe,但是随着M浓度的增加而减小,这是因为M的加入不仅会降低体系中Fe的浓度,而且还将影响Fe之间相互作用导致Fe磁矩下降。利用计算获得的系统总的电子态密度和Fe的电子态密度对计算结果进行了分析。     

不同表面除胶工艺对碳纤维本体结构和表面结构的影响

采用丙酮浸泡、瞬时高温处理及氮气保护下高温处理3种工艺对碳纤维表面进行除胶处理,利用场发射扫描(FESEM)、X射线光电子能谱(XPS)、X射线衍射(XRD)、激光拉曼光谱(LRS)等分析测试手段对不同除胶工艺处理的碳纤维性能进行了对比分析。结果表明,3种除胶工艺都不会破坏碳纤维的本体结构,但对碳纤维表面上浆剂的去除具有不同的效果。丙酮浸泡工艺效果不明显,瞬时高温处理在除胶的同时会破坏碳纤维的表面结构。氮气保护下高温处理工艺的设计避免了上浆剂高温裂解产物的残留,防止了碳纤维高温条件下表面性能的破坏,除胶效果最好。     

Distribution of magnetic moments and hyperfine fields for Fe/Cr multilayers with different interface roughness

Distribution of d-electron magnetic moments has been calculated within the Periodic Anderson Model (PAM) for Fe/Cr superlattices with various interface roughness. Special random algorithms were developed for the modelling of stepped interfaces with different average size of the steps as well as for the modelling of interface alloying. Self-consistent calculation of magnetic moment distribution for alloyed interfaces show strong correlation with hyperfine fields (hff) on Fe nuclei, measured by the Mössbauer spectroscopy. It allows one to correlate the hff with specific environment of interfacial Fe atoms and leads to the essential correction of the empirical approach for the interpretation of Mössbauer spectra. New criterion for the testing of smoothness of the interface using Mössbauer data is suggested.