Fe-Doped All-Boron Fullerene B_(40) with Tunable Electronic and Magnetic Properties as Single Molecular Devices

Systematic theoretical calculations are performed to investigate the dopant effect of Fe on stability, electronic and magnetic properties of the newly synthesized all-boron fullerene B40. The results reveal that as a typical ferromagnetic element, Fe atoms can either be chemically externally adsorbed on, or internally encapsulated in the cage of B40, with the binding energies ranging from 3.07 to 5.31 eV/atom. By introducing the dopant states from the doped Fe atom, the energy gaps of the Fe-doped B40-based metallofullerenes are decreased. Our spin-polarized calculations indicate that Fe-doped metallofullerenes have attractive magnetic properties: with alternative binary magnetic moments between 4.00μB and 2.00μB, depending on the resident sites of the doped Fe atom. The findings of the tunable electronic properties and binary magnetic moments of the Fe-doped B40-based metallofullerenes imply that this type of metallofullerene may be applied in single molecular devices.     

First principles study on the electronic structure and magnetism of Fe1-xCoxSi alloys

Electronic and magnetic properties of Fe1-xCoxSi alloys were investigated by using a full-potential linear augmented-plane-wave method based on density functional theory. Electronic structure calculation demonstrates that half-metallic property appears in the Fe-rich region of 0 〈 x ≤ 0.25, while the alloys turn out to be a magnetic metal for x 〉 0.25. The concentration dependence of the magnetic moment of the alloys can be understood by the fixed Fermi level at minority band in Fe-rich region, as well as at the majority band in Co-rich region. In Fe-rich alloys, the electronic structure and the magnetic properties at Fe site depend mainly on the spin-polarization of nearest neighbouring Co atoms, while in Co-rich alloys, these features at Co site arise mainly from the neighbours of Fe atoms.     

Strain-tuned magnetic properties in (Ga,Fe)Sb:First-principles study

In view of the importance of enhancing ferromagnetic(FM) coupling in dilute magnetic semiconductors(DMSs),the effects of strain on the electronic structures and magnetic properties of(Ga,Fe)Sb were examined by a first-principles study.The results of the investigation indicate that Fe_(Ga) substitution takes place in the low-spin state(LSS) with a total magnetic moment of 1μB in the strain range of-3% to 0.5%,which transitions to the high-spin state(HSS) with a total magnetic moment of 5μB as the strain changes from 0.6% to 3%.We attribute the changes in the amount and distribution of the total moment to the influence of the crystal field under different strains.The FM coupling is strongest under a strain of about0.5%,but gradually becomes weaker with increasing compressive and tensile strains.The magnetic coupling mechanism is discussed in detail.Our results highlight the important contribution of strain to magnetic moment and FM interaction intensity,and present an interesting avenue for the future design of high Curie temperature(T_C) materials in the(Ga,Fe)Sb system.     

The interplay between the lattice and magnetism in La(Fe_11.4Al_1.6)C_0.02 studied by powder neutron diffraction

The crystallographic structure and magnetic properties of La(Fe 11.4 Al 1.6 )C 0.02 are studied by magnetic measure- ment and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe 11.4 Al 1.6 )C 0.02 crystallizes into the cubic NaZn 13 -type with two different Fe sites: Fe I (8b) and Fe II (96i), and that Al atoms preferentially occupy the Fe II site. A ferromagnetic state can be induced at a medial temperature of 39 K–139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe 11.4 Al 1.6 )C 0.02 has no net magnetization in the paramagnetic (T > T N = 182 K) or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe–Fe bond length indicates that the ferromagnetic state prefers longer Fe–Fe distances.     

Electron transport properties of magnetic granular films

In this paper,we present a review of electron transport properties of magnetic granular films.Magnetic granular films are nanocomposite materials which consist of magnetic nanoparticles embedded in a nonmagnetic matrix or assembling of magnetic nanoparticles.According to the style of the nonmagnetic matrix,microstructure and the electron transport mechanism of the films,the magnetic granular films were divided into three groups:(1) magnetic metal-metal granular films,(2) magnetic metal-insulator granular films and(3) magnetic nanocluster-assembled granular films.Moreover,we also systematically review the magnetic properties,transport properties and magnetoresistance effect of size-monodispersed Co and Fe nanocluster-assembled films.     

Synthesis of high-TC ferromagnetic Mn-doped ZnO nanorods by thermal evaporation

This paper reports that a large amount of Mn-doped ZnO nanorods have been synthesized through thermal evaporation. The morphologies and properties are studied with x-ray diffraction, a scanning electron microscope, transmission electron microscope and Raman spectroscope. The results indicate that the manganese atoms occupy the zinc vacancies in the wurtzite lattice of ZnO without forming secondary phases. The exact manganese content has been studied by the x-ray fluorescence spectrum. Meanwhile, the magnetic moment versus temperature result proves that the as-prepared Mn-doped ZnO nanorods show ferromagnetic properties at temperatures as high as 400 K. These studies provide a good understanding of the origin of magnetic properties in diluted magnetic semiconductors.     

Magnetic Microstructure of Sintered Nd-Fe-B Magnets Made from Casting Strips

The magnetic microstructures of two Dy-AI substituted sintered Nd-Fe-13 magnets with the different nominal compositions of Nd12.2Vy0.6Fe80.4Al0.7B6 (at.%) (composition-A,C-A) and Nd13.7Dy0.6Fe78.8Al0.7B6.2(at.%)(composition-B,C-13) prepared by strip casting technique have been revealed by using a magnetic force microscope. The magnetic properties of sintered C-B magnets are worse than that of C-A sintered magnets. In particular, the value of density products (BH)max for sintered C-A magnets is about 32% higher than that of C-B magnets, which is reflected by their quite different magnetic microstructures. We believe that for the C-B samples, the inappropriate composition and thus the redundant Nd2Fe17(B) phase of the casting strips make its final magnetic microstructures worse than the C-A, and then deteriorates the performance of the C-B magnets.     

Magnetocaloric effects in RT X intermetallic compounds(R = Gd–Tm,T = Fe–Cu and Pd,X = Al and Si)

The magnetocaloric effect(MCE) of RT Si and RT Al systems with R = Gd–Tm, T = Fe–Cu and Pd, which have been widely investigated in recent years, is reviewed. It is found that these RT X compounds exhibit various crystal structures and magnetic properties, which then result in different MCE. Large MCE has been observed not only in the typical ferromagnetic materials but also in the antiferromagnetic materials. The magnetic properties have been studied in detail to discuss the physical mechanism of large MCE in RT X compounds. Particularly, some RT X compounds such as Er Fe Si,Ho Cu Si, Ho Cu Al exhibit large reversible MCE under low magnetic field change, which suggests that these compounds could be promising materials for magnetic refrigeration in a low temperature range.     

Unique Magnetic Moment and Electronic Properties for Fe（MgO）n（n=1-8） Clusters： First-Principles Calculations

The geometries and electronic properties of Fe（MgO）n are systematically investigated by the density functional theory. The results show that the doped Fe atom is prone to bond with the O atom, and Fe almost does not disturb the frame of （MgO）n. The second-order energy difference, the fragmentation energies and the electron amnities show that Fe（MgO）4 and Fe（MgO）6 possess relatively higher stabilities. The HOMO-LUMO gaps of Fe（MgO）n decrease obviously as compared with （MgO）n. Almost equal unpaired electrons of the 3d state of the Fe atom in Fe（MgO）n result in a nearly equal magnetic moment of Fe（MgO）n.     

Controlled adsorption of cytochrome c to nanostructured gold surfaces

Herein, we present a novel method based on the use of the symmetrical T4 bacteriophage capsid as a scaffold for preparing the gold-coated iron ternary core/shell nanostructure. Results showed that the thick gold shell was obtained to effectively protect Fe core from oxidation. Magnetic measurements showed that the nanocomposites were superparamagnetic at room temperature with a blocking temperature of about 35?K. At 3?K, its coercivity of 1142.86 Oe was larger than the existing experimental values. The magnetic property of Au/T4 was also tested, demonstrating the source of the magnetic sample arising from the Fe core only. The absorption spectrum of the Fe@Au/T4 complex was measured and compared with gold/virus. Different thickness gold shells were controlled in the synthesis by tuning the Au salt addition. On the basis of results and discussion, we further speculated the general growing mechanism of the template-supported Fe@Au process.     

A simple method to prepare the magnetic Ni@Au core‐shell nanostructure for the cycle surface enhanced Raman scattering substrates

We have developed a simple and efficient approach to synthesize Ni@Au core‐shell nanostructures using the simple redox transmetalation reaction. The as‐synthesized nanomaterial with clean and reproducible properties was used as the surface enhanced Raman scattering (SERS) substrate. In addition, these nanostructures are stable for at least a 30‐day period, and the long‐term stability is of the great importance in practical application. The magnetic behavior serves as an added advantage of its easy separation from the analytes. So that it can be reused. This novel multifunctional hybrid nanostructure will open up an exciting opportunity in multiple uses SERS measures. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative study of core–shell iron/iron oxide gold covered magnetic nanoparticles obtained in different conditions

In this study, we report the synthesis and characterization of the core–shell Fe covered with Au shells nanoparticles with mean diameters between 5 and 8 nm. The inverse micelles method was utilized to produce the samples. X-ray diffraction studies show that both core–shell systems have the expected crystalline structure. High resolution transmission electron microscopy and atomic emission spectroscopy techniques give additional information concerning the structure and composition of nanoparticles. An intermediate shell of amorphous oxidized iron was found between the magnetic Fe core and the external gold shell. The magnetic behavior of different core–shell samples shows no hysteresis loop indicating the superparamagnetic behavior of Fe@Au systems. The superparamagnetic behavior is also evidenced from FC and ZFC dependences of the magnetization versus temperature. By using the temperature dependence of the thermoremanent magnetization combined with magnetization versus applied magnetic field, the effective anisotropy constant was determined. The Fe/Au interface contribution to the effective anisotropy constant was calculated and discussed in relation with the combined shape and stress anisotropies.     

Clusters and magnetic anchoring points in (Ga,Fe)N condensed magnetic semiconductors

The stability and magnetic properties of Fe clusters in the (Ga,Fe)N magnetic semiconductor is investigated by using first-principles density functional theory and local spin density+Hubbard U theoretical methods. The present results reveal the existence of ferrimagnetic clusters formed by three or four peripheral Fe atoms neighboring a central Fe atom acting as a robust magnetic anchoring point. These clusters have magnetic moments 2 or 3 times that of a single Fe atom and, when connected by sharing peripheral Fe atoms, can form stable, ordered magnetic regions where all of the central atoms are ferromagnetically coupled. The formation of these ferrimagnetic clusters is proposed here to be at the origin of the ferromagnetic behavior observed in (Ga,Fe)N samples showing chemical phase separation.     

Correlation between ferromagnetic state and thermally stable layer of Fe on the W(001) surface

The variations of electronic and magnetic properties of ultrathin Fe overlayers on a W(001) surface as a function of Fe film thickness (1.0–4.0 ML) has been investigated using X-ray magnetic circular dichroism (XMCD) in conjunction with ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED). We found that the ferromagnetic property of Fe film started to build up over 2.0 ML, as we confirmed the spin and angular moment contribution to the magnetic moment using XMCD experiments. We also confirmed that a thermally stable layer is over 2.0 ML of Fe film as we change the annealing temperature taken after Fe deposition at 300 K and at 400 K using UPS. We will systematically demonstrate that the occurrence of ferromagnetic property of Fe film on a W(001) surface is closely correlated to a thermally stable layer of Fe film on a W(001) surface.     

Block spin ground state and three-dimensionality of (K,Tl)(y)Fe(1.6)Se2

The magnetic properties and electronic structure of (K,Tl)(y)Fe(1.6)Se(2) is studied using first-principles calculations. The ground state is checkerboard antiferromagnetically coupled blocks of the minimal Fe(4) squares, with a large block-spin moment ～11.2 μ(B). The magnetic interactions could be modeled with a simple spin model involving both the inter- and intrablock, as well as the nearest-neighbor and next-nearest-neighbor couplings. The calculations also suggest a metallic ground state except for y=0.8 where a band gap ～400-550 meV opens, showing an antiferromagnetic insulator ground state for (K,Tl)(0.8)Fe(1.6)Se(2). The electronic structure of the metallic (K,Tl)(y)Fe(1.6)Se(2) is highly three dimensional with unique Fermi surface structure and topology. These features indicate that the Fe-vacancy ordering is crucial to the physical properties of (K,Tl)(y)Fe(2-x)Se(2).     

Polarized neutron reflectometry of the influence of Fe/Si,Fe/FeSi2 and Au/Fe interfaces on the magnetic properties of epitaxial Fe films

The magnetic and structural properties of epitaxial Fe films grown on Si(1 1 1) are investigated by polarized neutron reflectometry (PNR) at room temperature. The influence of different types of interfaces, Fe/Si, Fe/FeSi₂ and Au/Fe on the magnetic properties of Fe films deposited by molecular beam epitaxy onto Si(1 1 1) are characterized. We observe a drastic reduction of the magnetic moment in the entire Fe film deposited directly on the silicon substrate essentially due to strong Si interdiffusion throughout the whole Fe layer thickness. The use of a silicide FeSi₂ template layer stops the interdiffusion and the value of the magnetic moment of the deposited Fe layer is close to its bulk value. We also evidence the asymmetric nature of the interfaces, Si/Fe and Fe/Si interfaces are magnetically very different. Finally, we show that the use of Au leads to an enhancement of the magnetization at the interface.     

形貌可控的Fe3O4纳米粒子的水热合成及磁性能研究

Fe3O4是一种重要的磁性材料.由于其独特的光、电、磁、热等性能而备受关注.在本文中,我们采用水热溶剂热法合成了Fe3O4磁性纳米粒子.利用X-射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）和振动样品磁强计（VSM）对产物的结构、形貌及磁性能进行了研究.结果表明,通过前驱物的适当选择,可以实现Fe3O4纳米粒...     

Magnetic anisotropy and magnetization dynamics of Fe nanoparticles embedded in Cr and Ag matrices

Static and dynamical magnetic properties of Fe nanoparticles (NPs) embedded in non-magnetic (Ag) and antiferromagnetic (Cr) matrices with a volume filling fraction (VFF) of 10% have been investigated. In both Fe@Ag and Fe@Cr nanocomposites, the Fe NPs have a narrow size distribution, with a mean particle diameter around 2 nm. In both samples, the saturation magnetization reaches that of Fe bulk bcc, suggesting the absence of alloying with the matrices. The coercivity at 5 K is much larger in Fe@Cr than in Fe@Ag as a result of the strong interaction between the Fe NPs and the Cr matrix. Temperature-dependent magnetization and ac-susceptibility measurements point out further evidence of the enhanced interparticle interaction in the Fe@Cr system. While the behaviour of Fe@Ag indicates the presence of weakly interacting magnetic monodomain particles with a wide distribution of blocking temperatures, Fe@Cr behaves like a superspin glass produced by the magnetic interactions between NPs.     

An in-situ study of structure and magnetic properties of Fe films on the sulphur passivated Ge(100) surface at 150°C

Ultra-thin Fe films have been grown on the sulphur passivated Ge(100) surface at 150°C. The growth, structure and the magnetic properties of the thin films were studied with LEED, AES, angle resolved AES and in-situ magneto-optical Kerr effect measurements. For the first five monolayers of Fe, no long-range order was observed . However, angle resolved AES data suggest that local order occurs with a small fraction of the Fe atoms adsorbed on bcc sites. For thicker Fe films, the growth becomes ordered. A comparison of the present study and with a previous study of the growth of Fe on sputter cleaned Ge(100)(2×1) surface, shows that sulphur passivation effectively prevents Fe–Ge intermixing. During the Fe deposition process, most of the sulphur atoms migrate to the growing surface, thus acting as surfactants. The presence of sulphur at the surface also affects the growth and magnetic properties of the thin films.