DISSOLUTION OF IRON TO COPPER IN Fe60Cu40 ALLOY BY MECHANICAL ALLOYING AND SUBSEQUENT DECOMPOSITION

A metastable alloy with composition Fe₆₀Cu₄₀ can be prepared in single phase of a fcc structure by mechanical alloying, although Fe-Cu system is virtually immiscible in its equilibrium state at ambient temperature. The M?ssbauer spectra of this supersaturated solid solution could be fitted by two subspectra whose hyperfine magnetic fields are 200 kOe and 250kOe. In this metastable alloy, the iron atoms at the interface are easy to form clusters characterized as α-Fe at a temperature below 250℃, whereas the iron atoms in the body will cluster together at a higher temperature above 350℃ and behave as γ-Fe, and then transform to ferromagnetic bcc iron occurs.     

FMR studies in Al2+ implanted Fe60Al40 alloy

The Al²⁺ implanted layer (∼ 200 nm) in Fe₆₀Al₄₀ has been investigated by FMR. The magnetization is found to be 6400 G in the absence of anisotropy which agrees well with the value reported on cold worked Fe₆₀Al₄₀. Smaller line width for a sample implanted with the highest fluence of 1×10¹⁵ ion/cm² indicates better chemical and magnetic homogeneities. The g-factor is 2.06.     

Near-harmonic structure and level similarities in Fe56, Fe58 and Ni60

Near-harmonic structure is known to exist in Fe⁵⁸, and an investigation was undertaken to determine whether this structure is also present in Fe⁵⁶, and Ni⁶⁰. In the case of Fe⁵⁶, no second 2⁺ state with the desired energy or de-excitation characteristics had been reported by previous investigators and a search for a small excitation of such a level from the decay of Mn⁵⁶ is described. The results are inconclusive although some evidence for its existence is presented. Our investigation of the Mn⁵⁶-Fe⁵⁶ decay reveals the presence of an additional beta branch to a 2⁺ level at 3.34 Mev in Fe⁵⁶. The results of the angular correlation measurements on the cascade gamma rays from this and other levels are given. The stopover transitions are found to be mostlyM 1 radiation and hence not of the near-harmonic type. In the case of Ni⁶⁰, the measured angular correlation functions for the 0.85–1.33 and 1.76–1.33 Mev cascades initiated from the decay of Cu⁶⁰ are reported. For the former cascade, the results indicate that the stopover transition is largely E2 radiation, but the experimental difficulties prevent a more quantitative statement. The presence of this type of radiation, together with a stopover to crossover intensity ratio of 15, imply the existence of near-harmonic structure in Ni⁶⁰. The angular correlation function for the latter cascade is found to be nearly identical to that of the corresponding cascade in Fe⁵⁸ which lends weight to the contention that there exist level similarities in these nuclei. Additional evidence for these similarities is also presented.     

A STUDY OF THE CRYSTALLIZATION OF AMORPHOUS Cu60Zr40 ALLOY

The crystallization of the amorphous Cu₆₀Zr₄₀ alloy has been studied by differential scanning calorimetry (DSC), scanning Auger microprobe (SAM) and transmission electron microscopy (TEM). The DSC trace showed that the sample exhibited a glass transition at 750 K and a strong exothermic effect beginning from 782 K. An enrichment of the element Zr and significant oxygen contamination in a zone near the surface to a depth of about 10 nm were revealed by SAM in the analysis of surface competition and depth profiles of the Cu₆₀Zr₄₀ sample. Also, the change of concentration ratio of Ca to Zr in amorphous matrix at the clean Cu₆₀Zr₄₀ surface as a function of annealing temperature was examined in detail, and it was found that the concentration of Zr at the surface is slightly higher than that in the bulk until 780K and that the concentration ratio of Cu to Zr in matrix has an abrupt increase in the temperature range of 780-800K. The observations by high resolution TEM revealed the appearance of cluster-like regions of approximately 1.5-2.0 nm in size just before crystallization and they distributed randomly throughout the sample. This phenomenon is analogous to the results obtained using field ion microscopy (FIM) by the present authors. The microstructural changes of the sample daring heating show the gradual crystallization of the amorphous matrix.     

Crystallographic structure of ultrathin Fe films on Cu(100)

We report the observation of bcc-like crystal structures in 2-4 monolayer (ML) Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The nonpseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness, is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.     

Self-organization processes in the cellular structure formation of Ni-W alloys

The self-organization processes, the growth steadiness, and the stability of the cellular structure morphology of Ni-W alloy single crystals with a tungsten concentration of 25–40% have been investigated. The temperature gradient in the crystallization front, the oriented crystallization rate, doping with aluminum, titanium, chromium, and molybdenum, and the tungsten concentration have been considered as nonequilibrium factors. The nonlinear dependence of the structure characteristics on the growth parameters, including the temperature gradient, the oriented crystallization rate, and the tungsten concentration, has been determined. Dendrite features of the cellular morphology of the crystallization front are the result of the self-organization processes and promote the steady growth of single crystals with a high degree of structural perfection. A mechanism of the morphological transition from hexagonal to square cells has been proposed.     

Surface structure of ultrathin Fe films on Cu(001) revisited

The structure and magnetism of ultrathin Fe films epitaxially grown on a Cu(001) surface are investigated by grazing scattering of fast H and He atoms or ions. By making use of a new variant of ion beam triangulation based on the detection of the number of emitted electrons, we obtain direct information on the structure of the film surface. We observe for room temperature growth a dominant and defined fcc-like structure. Complex surface reconstructions as reported in recent STM and LEED studies are observed only for cooling and H2 dosing.     

Structural separation of amorphous Fe40Ni40P14B6 alloy during natural ageing

Both the transmission and depth selective conversion electron Mössbauer spectroscopy (DCEMS) were applied usefully to study structural transformations in the bulk and in the surface layer ～50 and 100 nm thick during three years natural ageing of an amorphous alloy. The primary crystallization was revealed in the surface layer ～100 nm thick on the rough side of amorphous ribbon.     

Fe含量和粒径对Fe/Cu颗粒膜结构和磁性的影响

采用共蒸发法制备不同组分的Fe/Cu颗粒膜,将样品分两组进行退火和不退火处理. 根据测量及分析,确定了不同成分的Fe/Cu颗粒膜的相组成和晶体结构;找出了 Fe/Cu颗粒膜矫顽力与粒径的关系,利用此关系由自发形核理论可知,提高功率,快速蒸镀薄膜,可得到细密颗粒的Fe/Cu颗粒膜,从而降低矫顽力,减少磁滞损耗.     

Self-organization of the stripe domain structure in oblique-evaporated quantum wells in vacuum

The dependence of the domain structure of oblique-evaporated quantum wells on their thickness and the angle of inclination of the easy-magnetization axis with respect to the normal to the quantum well plane has been studied. It is found that the self-organization of domain structures is mainly related to the quantum character of the cooperative phenomenon.     

19芯Fe/Cu复合包套二硼化镁超导线制备及其超导性能研究

采用In-Situ PIT方法,以工业级低纯度B粉(92%)和镁粉(99%)为原料制备了19芯Fe/Cu复合包套MgB2超导线。断面扫描电镜观测表明,超导线内部超导芯分布排列均匀,Fe层都能完好包围MgB2芯体,Fe与Cu层结合紧密,填充因子0.17。750℃热处理1h后,样品超导转变温度Tc(onset)=33.5K,转变宽度ΔTc=4.8K。X光衍射检测发现,MgB2超导相中不存在其它Mg-B化合物杂项,但含有少量MgO和FeB2。多芯化后,超导芯中FeB2略有增加。四引线Ic测试发现,19芯样品在4.2K,4T时,临界电流密度为5622A/cm2,比单芯样品14400 A/cm2降低约2/3。     

Local atomic structure of ultra-thin Fe films grown on Cu(100)

Ultra-thin epitaxial Fe films grown by thermal deposition on Cu(100) are analyzed by scanning tunneling microscopy. Evidence is presented that the morphological characteristics and magnetic properties are a direct consequence of FCC-to-BCC transitions reminiscent of those occurring in bulk Fe. In contrast to the assumption of a ferromagnetic FCC phase in previous models of the Fe/Cu(100) system, we observe a tightly twinned and strained BCC-like phase termed nanomartensite in films below 5 ML thickness, which encompasses almost the entire film volume of 3 ML films. In addition, the surface of 7–8 ML films reconstructs by forming non-close-packed structures with BCC-like bond angles. The formation of these BCC-like phases is the reason for the expansion of the interlayer spacing observed in these films and correlates perfectly with their ferromagnetic ordering. PACS 68.55.-a; 64.70.-p; 81.30.-t     

Self-organization of atomic order and electronic structure in LaSrMnO films

A linear relationship between the critical temperatures T_max and T_min in the temperature dependences of the resistance of La_0.6Sr_0.2Mn_1.2O₃ single-crystal films that have a mesoscopic irregularity (metallic clusters in an insulating matrix) is found. A correlation between the atomic order and electronic structure of the films is studied by taking X-ray diffraction patterns and optical absorption spectra. It is shown that a rise in T_max and a simultaneous decrease in T_min cause correlated local changes in cluster areas of the structure. Namely, the volume occupied by a family of Mn-O planes with large interplanar spacings (d=2.04–2.08 Å) shrinks, while the volume occupied by a family of closer spaced (d=1.90–1.99 Å) planes grows. In the electronic subsystem, the density of states at ?ω=1.5 and 2.4 eV, which are due to Mn³⁺ and Mn⁴⁺ ions, increases, and the contribution from Mn²⁺ states at ?ω=0.9 eV decreases. As the charge states associated with Mn³⁺ and Mn⁴⁺ ions become dominant, the Mn-O binding energy grows. As a result, the contribution of the structural states with smaller d increases, thereby raising the density of states in the electronic subsystem at energies between 0.5 and 2.7 eV. The effect of self-organization in the multicomponent LaSrMnO system shows up in the transition from the heavily distorted rhombohedral to the less distorted orthorhombic structure.     

Influence of annealing on the structure and optical properties of Zn40Se60 thin films

Thin films of Zn₄₀Se₆₀ were prepared by the vacuum thermal evaporation technique. The influence of annealed temperature on the structural and optical properties was investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical transmission. The XRD studies show that the as-deposited film is amorphous in nature, but the crystallinity improved with increasing the annealing temperature. Furthermore the particle size and crystallinity increased whereas the dislocation and strains decreased with increasing the annealing temperature. SEM studies showed that the annealing temperature induced changes in the morphology of the as-deposited sample. Various optical constant have been calculated for as-deposited and annealed films. The mechanism of the optical absorption follows the rule of direct transition. It was found that, the optical energy gap (E_g) decreased with increasing the annealing temperature. These results can be interpreted by the Davis and Motte model. On the other hand the maximum value of the refractive index (n) is shifted toward the long wavelength by increasing the annealing temperature.     

Structural segregation in amorphous Fe40Ni40P14B6 under heat treatment and natural ageing

Transmission and depth selective conversion electron Mössbauer spectroscopy (DCEMS) were applied usefully to study structural transformation in the bulk and in the surface layer in a≈50 and 100 nm thick amorphous alloy that was subjected to annealing and natural ageing. Analysis of the hyperfine field distributionsP(H) shows the segregation of the amorphous matrix.     

Coupled perpendicular magnetization in Fe/Cu/Fe trilayers

Ultrathin epitaxial Fe films on Cu(1 0 0) with perpendicular magnetization have been used as templates for the preparation of FCC Fe/Cu/Fe trilayers. The magnetic anisotropy and the coupling of these films have been studied by in-situ magneto optical Kerr effect measurements and Kerr microscopy. The magnetic coupling of both Fe layers is found to be dominated by magnetostatic interaction. Adsorbate-induced spin reorientation in the top layer also causes spin reorientation in the bottom layer. The governing role of the Fe-vacuum interface for the magnetism of the whole trilayer is demonstrated.