A study of Fe--N alloy systems

Magnetic properties of Fe nitrides have been reexamined by ⁵⁷Fe Mössbauer spectroscopy. Hyperfine magnetic fields for α″-Fe₁₆N₂, γ′-Fe₄N, ε-Fe₃N, ζ-Fe₂N, NaCl-type FeN and ZnS-type FeN have been determined at various temperatures. Although α′-, γ″-, and ε-nitride are all ferromagnets, ζ-Fe₂N is found to be an antiferromagnet below 9 K and ZnS-type FeN is non-magnetic at 4.2 K. Contrary to the ZnS-type FeN, the NaCl-type FeN is an antiferromagnet and shows a component with a surprisingly large hyperfine magnetic field of 49 T.     

O_2在FeN_4掺杂碳纳米管上氢化特性的密度泛函理论研究

因其速率快、稳定性高,非金属N与金属共掺杂的碳材料作为新型高效ORR催化剂而引起了人们的广泛关注.采用包含色散力校正的密度泛函理论方法系统地研究了氧分子在FeN_4掺杂的碳纳米管上的吸附、氢化特性.结果表明:(1)O_2倾向于以end-on模式吸附在Fe顶位,O-O键与衬底表面成一定角度,并指向五元环,对应的吸附能为1.62 e V.(2)O_2在FeN_4-CNTs上更倾向于直接氢化为OOH,然后解离为O+OH,整个路径的限速步为OOH的解离,对应的势垒为1.19 eV.     

Investigating the surface morphology and magnetic contrast of epitaxial ferromagnetic structures

The surface morphology of nickel thin films is investigated via atomic force microscopy. The multistage film growth mechanism is found to be dependent on substrate temperature and film thickness. It is shown that conduction electron scattering from the irregularities of the outer and inner surfaces of structures are influenced by the surface morphology and determined by an integrated contribution of the surface’s fluctuation density spectrum. The morphology influence can be decreased under certain growth conditions so that the residual mean free path of conduction electrons can reach 1000 nm, exceeding the film thickness. Epitaxial nanostructures with high electron mobility have been fabricated. Investigation of their magnetic structure has shown that their magnetic domain dimensions are less than the residual mean free path of electrons determined by the surface morphology.     

稀土永磁薄膜材料

简要地介绍在纳米复合稀土永磁薄膜材料、各向异性稀土永磁薄膜材料方面的进展。在纳米复合稀土永磁薄膜材料中实现磁性交换耦合和剩磁增强效应，系统地研究了其结构与磁性的关系。制备成功高磁能积的各向异性稀土永磁薄膜材料，比较了Ti或Mo缓冲层对Nd-Fe-B薄膜的表面形貌、磁畴结构和磁性能的影响。发现薄膜的表面形貌强烈地依赖于缓冲层的厚度。由于它极大地影响薄膜的成分，溅射速率被证明是控制薄膜的显微结构、表面形貌和磁性能的一个重要因素。在微磁学模型的基础上，通过分析从5到300K的矫顽力温度依赖关系。研究了各向异性Pr-Fe-B薄膜的矫顽力机制。在晶粒表面，由于磁各向异性的降低和局域退磁场的提高导致的反转畴的形核被确定为控制各向异性Pr-Fe—B薄膜的磁化反转过程的首要机制。     

The structures and electronic properties of ferrous nitride–fulminic acid clusters

The structures and electronic properties of ferrous nitride–fulminic acid (FeN–HCNO) clusters are investigated by using PW91 functional. The results reveal that the Fe atom of an FeN molecule prefers to be absorbed on the N–O of an HCNO molecule and it shows the highest kinetic stability. The Fe–N–C–N ring structure has the highest kinetic stability, while the FeN–HCNO chain configuration shows the highest kinetic activity. The N–Fe–ONCH chain structure displays the maximum dipole magnitude (DM) value (8.246 Debye). The Fe atom of the FeN molecule adsorbed on the C atom of the HCNO molecule has the minimum DM value (0.641 Debye). The linear FeN–HCNO configuration displays the largest total spin (2.945?μ_B/atom). The hybridization of sp orbital of the FeN–HCNO clusters is very important.     

Magnetic properties of small Fe clusters: a nonorthogonal H amiltonian study

We calculate the magnetic properties of small FeN clusters(N=2～7,9,13,15) by using a parameterized Hubbard tight-binding sp d-band model Hamiltonian, with the parameters obtained from nonorthogonal Ham il tonian parameters. the average magnetic moments, and the spin-polarized charge distribution within clusters are in agreement with those obtained by first-prin ciple and tight-binding calculations. The effect of the nonorthogonal basis is discussed.     

FeN_4掺杂对富勒烯催化特性调制的第一性原理研究

因其较好的稳定性和催化活性,非金属N与金属共掺杂的富勒烯(C60)作为新型氧化还原反应(ORR)催化剂受到了人们的广泛关注.采用基于密度泛函理论的第一性原理方法系统地研究了Fe N4掺杂对C60催化特性的调制规律,揭示了O_2在Fe N4掺杂的C60上的吸附和氢化特性.结果表明:(1)O_2倾向于以side-on模式吸附在Fe的顶位上,O-O键平行于C60的球切面,与Fe形成O-Fe-O三元环结构,对应的吸附能为1.48 e V.(2)O_2的氢化反应路径可以分为两条:(i)O_2先解离为O+O,然后氢化为O+OH.O_2的解离为反应的速控步,势垒为2.82 e V.(ii)O_2先氢化形成OOH结构,然后解离.氢化为反应的速控步,势垒为2.83 e V.     

FeN4掺杂对富勒烯催化特性调制的第一性原理研究

因其较好的稳定性和催化活性,非金属N与金属共掺杂的富勒烯（C60）作为新型氧化还原反应（ORR）催化剂受到了人们的广泛关注。采用基于密度泛函理论的第一性原理方法系统地研究了FeN4掺杂对C60催化特性的调制规律,揭示了O2在FeN4掺杂的C60上的吸附和氢化特性。结果表明：（1）O2倾向于以side-on模式吸附在Fe的顶位上,O-O键平行于C60的球切面,与Fe形成O-Fe-O三元环结构,对应的吸附能为1.48 eV。（2）O2的氢化反应路径可以分为两条：（i）O2先解离为O + O,然后氢化为O + OH。O2的解离为反应的速控步,势垒为2.82 eV。（ii）O2先氢化形成OOH结构,然后解离。氢化为反应的速控步,势垒为2.83 eV。     

外加磁场对磁控溅射制备氮化硅陷光薄膜的影响

在基底与靶材之间放置磁性强弱不同的永久磁铁来研究外加磁 场对磁控溅射制备氮化硅陷光薄膜的影响. 通过X射线衍射、原子力显微镜 (AFM) 以及紫外分光光度计分别测试了外加磁场前后所制备薄膜的组织结构、表面形貌和光学性能. 结果表明, 外加磁场后, 氮化硅薄膜依然呈现非晶结构; 但是表面形貌发生明显改变, 中心磁场1.50 T下, 薄膜表面为特殊锥状尖峰结构"类金字塔"的突起, 而且这些突起颗粒垂直于基底表面; 在 可见光及近红外范围内, 中心磁场1.50 T 下的薄膜样品平均透射率最大, 平均透射率达到90% 以上, 比未加磁场的样品提高了近1 倍, 具有很好的陷光特性. 关键词： 外加磁场 磁控溅射 氮化硅薄膜 陷光效应     

A new TiW seed layer for SmCo5 films with perpendicular magnetic anisotropy

A new seed layer TiW is proposed for SmCo₅ films with perpendicular magnetic anisotropy. The influence of a TiW seed layer on the microstructure and the surface morphology of Cu underlayer are studied. The grain size and surface roughness dependence of Cu underlayer on the thickness and the annealing of the TiW seed layer are also investigated. The improvement in the perpendicular magnetic properties of SmCo₅ film from the TiW seed layer is approved. The results show that a 5 nm Ti₃W₇ seed layer improves the microstructure and surface morphology of Cu underlayer, and significantly improves the perpendicular magnetic properties of SmCo₅ film. The diffusion barrier and a high melting point of the TiW seed layer are regarded as the physical mechanism of the improvement for SmCo₅ film with perpendicular magnetic anisotropy.     

57Fe Mössbauer study of Fe nitrides

Summary Magnetic properties of Fe nitrides have been re-examined by⁵⁷Fe M?ssbauer spectroscopy. Hyperfine magnetic fields for α″-Fe₁₆N₂ are 30, 31 and 39T at 298K, but the averaged hyperfine field is 33T and nearly equal to the value of pure α-Fe. σ-Fe₂ N is an antiferromagnet below 9K having a small magnetic moment less than 0.1 μ_B, although γ′-Fe₄N and ε-Fe_3–2N are ferromagnets. ZnS-type FeN is non-magnetic at 4.2K. M?ssbauer spectra obtained from NaCl-type FeN are complex and some Fe atoms in this nitride show a surprisingly large hyperfine magnetic field of 49T. Paper presented at the ICAME-95, Rimini, 10–16 September 1995.     

The effect of magnetic field on the electrodeposition of CoFe alloys

The superimposition of a homogenous magnetic field during an electrodeposition of CoFe alloy was investigated. A magnetic field superimposed parallel to the electrode surface increases the limiting current density and the deposition rate due to the magnetohydrodynamic (MHD) effect. The deposits obtained in this field configuration appear smoother and more homogenous than the ones obtained without the magnetic field. On the contrary, a magnetic field superimposed perpendicular to the electrode surface does not influence significantly the electrochemical reaction but the morphology of the deposited layers is strongly affected. The roughness is strongly increased in this field configuration and grains grow as separated columns aligned perpendicular to the electrode surface, in the field direction. A magnetic field applied during the deposition affects the magnetic properties of the deposited layers as well. These changes are discussed with respect to the surface roughness and the internal stress state of the layer.     

Porphyrin-like porous nanomaterials as drug delivery systems for ibuprofen drug

In recent years, nanomaterial-based drug delivery carriers have become some of the most attractive to be studied. The purpose of this study is to investigate the interaction of C60 fullerene, carbon nanotube and graphene having porphyrin-like FeN4 clusters with a non-steroidal anti-inflammatory drug (ibuprofen) by means of the density functional theory. Results showed that the graphene with FeN4 clusters could remarkably increase the tendency of graphene for adsorption of ibuprofen drug. Also, our ultraviolet–visible results show that the electronic spectra of the complexes exhibit a blue shift toward lower wavelengths (higher energies). It was found that Ibp/FeN4-graphene had high chemical reactivity, which was important for binding of the drug onto the target site. In order to go further and gain insight into the binding features of considered systems with ibuprofen drug, the Atoms in Molecules analysis was performed. Our results determine the electrostatic features of the Ibp/FeN4-graphene bonding. Consequently, the results demonstrated that the FeN4-graphene could be used as potential carriers for the delivery of ibuprofen drug.     

Growth parameter dependence of magnetic property of CrAs thin film

This paper has systematically investigated the substrate temperature and thickness dependence of surface morphology and magnetic property of CrAs compound films grown on GaAs by molecular-beam epitaxy. It finds that the substrate temperature affects the surface morphology and magnetic property of CrAs thin film more potently than the thickness.     

Study of nanoconductive and magnetic properties of nanostructured iron films prepared by sputtering at very low temperatures

A combined study of the surface nanostructure and electrical characteristics of iron thin films prepared on naturally passivated silicon wafers is presented. By means of conductive-scanning force microscopy, the influence of the substrate temperature during film preparation on both surface morphology and conductivity response is investigated. In addition, magnetic properties of these films are reported and correlated with the nanostructural properties. Films prepared at 200 K show granular core–shell magnetic behaviour exhibiting exchange bias. Both conductive and magnetic data indicate that samples prepared at low temperature behave as a percolated network of nanometric metallic iron clusters (with typical sizes of 20 nm) interconnected by oxidized chains (of 10 nm in diameter), showing an excellent system for nanotechnological exchange bias applications.     

Fabrication of Anodic Aluminum Oxide Templates with Small Interpore Distances

The influence of the electropolishing and anodization voltage on surface morphology has been carefully studied for fabrication of ordered anodic aluminum oxide （AAO） templates. In accordance with that in the anodization experiment, the size of small patterns on the foil surface formed from the electropolishing treatment increases with voltage. Using a combined method of small-voltage eleetropolishing and anodization, we have fabricated well ordered templates with much smaller interpore distances compared with that under normal-voltage fabrication conditions. The Ni nanowire arrays with two small diameters are eleetrodeposited through the above templates, exhibiting different magnetic properties. This also helps us to clarify the inner structure of this kind of templates.     

Changes in the hyperfine interactions in the Fe80Nb3Cu1B16 metallic glass under tensile loading

The influence of tensile stress on the changes in hyperfine parameters obtained by Mössbauer spectroscopy of the ferromagnetic amorphous NANOPERM-type Fe₈₀Nb₃Cu₁B₁₆ alloy has been investigated. The bulk changes are obtained by Mössbauer spectroscopy in a transmission geometry using γ-rays; the surface properties are studied in a scattering geometry using conversion electrons. The Mössbauer spectra are analyzed by two distributions of hyperfine inductions, which result in high-field and low-field components corresponding with a model of clusters formed by predominantly iron atoms and intermediate phase containing mainly the Nb, Cu and B atoms. The obtained results are completed by the bulk and surface magnetic measurements, with observations of surface morphology by AFM and microstructure by SEM. The investigations yield approximately linear increase of hyperfine parameters and slight deterioration of the bulk as well as surface magnetic characteristics with tensile loading.     

Fe and N diffusion in nitrogen-rich FeN measured using neutron reflectometry

Grazing incidence neutron reflectometry provides an opportunity to measure the depth profile of a thin film sample with a resolution <1 nm, in a non-destructive way. In this way the diffusion across the interfaces can also be measured. In addition, neutrons have contrast among the isotopes, making it feasible to measure the self-diffusion. In the present work, the isotope multilayers of [FeN/⁵⁷FeN]₁₀ and [FeN/Fe¹⁵N]₁₀ were prepared using magnetron sputtering and self-diffusion of Fe and N was investigated. It was found that N diffusion is slower compared to Fe and does not follow the atomic size dependence.      

Morphology induced magnetic instabilities on oxide antiferromagnetic surfaces

The role of interfacial disorder and roughness has been pointed out several times in ferromagnetic-antiferromagnetic exchange coupled systems. However, effect of surface morphology on magnetic properties of bare antiferromagnetic material has been mostly ignored. Here we report our experimental observations of magnetic instabilities on high temperature air annealed NiO(100) surfaces through treatment of successive vacuum and oxygen annealing above Néel temperature. Preferential spin-orientations are found to be governed by surface morphology with enhanced roughness and oxygen diffusion process. Stable domain distribution has been observed on smoother surfaces, which are found to be mostly inactive to these annealing treatments.     

The growth of soft magnetic FeNiN thin films under different experimental procedures

FeNiN thin films with good soft magnetic properties were synthesized on Si (1 0 0) substrates at 473 K by RF magnetron sputtering. The dependence of phase structure and magnetic properties on nitrogen partial pressure, nickel concentrations, film thickness and substrate temperature were systematically investigated. The phase evolution from α-(Fe,Ni)N to ξ-(Fe,Ni)₂N with increase of nitrogen partial pressure was seen. The addition of Ni caused FeNiN films to turn from BCC structure to FCC structure. Clear reproducible striped domains appeared at the film surfaces when X_Ni=19.6%, which is explained by the high enough perpendicular anisotropy and the small stress in the film. All films show smooth surfaces and good soft magnetic properties compared to corresponding FeN compounds. The magnetic properties depended dramatically on the phase structure. Optimum soft magnetic properties with H_C of <1 Oe are obtained between 5.0%?X_Ni?10.0%.