Stabilization of high spin FCC Fe in (Fe/Pd)n multilayers

Polycrystalline (Fe/Pd)_n multilayers are grown onto sapphire substrates at room temperature in a UHV system. The number of periods n=40 and the thickness of Pd layers of t_Pd=4 nm are kept constant, whereas the thickness of the Fe layers is varied from 1.5 to 5 nm. Structural properties are studied by in situ reflection high energy diffraction (RHEED), scanning tunnelling microscopy (STM) and ex situ by X-ray diffraction at small angles and large angles. Analyzing the experimental data using the program SUPREX we obtain interplanar distances of d_Fe=2.03±0.01 Å for an Fe layer thickness larger than about 2.5 nm as expected for (1 1 0) planes of BCC Fe. For Fe layers with thicknesses less than about 2.5 nm the interplanar distance is d_Fe=2.1±0.01 Å, which is close to the distance between (1 1 1) planes of FCC Fe with a lattice parameter of a=3.64 Å. Magnetic susceptibility measurements at temperatures between 1.5 and 300 K for (Fe/Pd)_n multilayers with FCC Fe yield a magnetic moment per Fe atom of μ=2.7±0.1 μ_B, which is about 20% larger compared to μ=2.2 μ_B for BCC Fe. We show that the occurrence of the large magnetic moment originates from FCC Fe being in the high spin (HS) state rather than from polarization effects of Pd at Fe/Pd interfaces.     

First-principles study of structural, electronic and magnetic properties in Cd1−xFexS diluted magnetic semiconductors

In this paper, we report theoretical investigations of structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Cd_1−xFe_xS with x=0.25, 0.5 and 0.75 in zinc blende (B3) phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the density functional theory and the generalized gradient approximation. The analysis of band structures, density of states, total energy, exchange interactions and magnetic moments reveals that both the alloys may exhibit a half-metallic ferromagnetism character. The value of calculated magnetic moment per Fe impurity atom is found to be 4 μ_B. Moreover, we found that p-d hybridization reduces the local magnetic moment of Fe from its free space charge value of 4 μ_B and produces small local magnetic moments on Cd and S sites.     

First-principles study on the electronic structures of iron phthalocyanine monolayer

The electronic band structure and magnetic properties of iron phthalocyanine (FePc) monolayer were investigated by using the first-principles all-electron full-potential linearized augmented plane wave energy band method. It is found that the ferromagnetic FePc monolayer is energetically more stable than the paramagnetic one. The exchange interaction, which splits the majority and minority bands, influences strongly on the electronic structure near the Fermi level (E_F). Magnetic moment of the central Fe atom is calculated to 1.95 μ_B. The range of the positive polarization of Fe site is larger in the out-of-plane than in the in-plane direction. The FePc ligand remains paramagnetic. The presence of states at E_F indicates the metallic character of FePc monolayer both for the paramagnetic and ferromagnetic states. However, the large density of states at E_F of the majority spins in the ferromagnetic state is expected to cause a phase transition to insulating antiferromagnetic state from the metallic ferromagnetic one.     

Microstructure, magnetic and optical properties of sputtered polycrystalline ZnO films with Fe addition

Microstructure, magnetic and optical properties of polycrystalline Fe-doped ZnO films fabricated by cosputtering with different Fe atomic fractions (x_Fe) have been examined systematically. Fe addition could affect the growth of ZnO grains and surface morphology of the films. As x_Fe is larger than 7.0%, ZnFe₂O₄ grains appear in the films. All the films are ferromagnetic. The ferromagnetism comes from the ferromagnetic interaction activated by defects between the Fe ions that replace Zn ions. The average moment per Fe ion reaches a maximum value of 1.61 μ_B at x_Fe = 4.8%. With further increase in x_Fe, the average moment per Fe ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Fe ions. The optical band gap value decreases from 3.245 to 3.010 eV as x_Fe increases from 0% to 10%. Photoluminescence spectra analyses indicate that many defects that affect the optical and magnetic properties exist in the films.     

非晶态(Fe1-xVx)84B16合金的磁性和电性

用单辊急冷法制备了非晶态(Fe_1-xV_x)₈₄B₁₆(x=0,0.02,0.04,0.06,0.10)合金的薄带,分别用磁天平和四端引线法测量了饱和磁化强度和高温电阻率的温度关系。得到平均每个磁性原子的磁矩随V含量的增加近似线性下降,计算出每个Fe原子和每个V原子的平均磁矩分别为2.08μ_B和-5.08μ_B。居里温度T_c从x=0时的622K下降到x=0.10时的478K。利用自旋波激发公式:σ(T)=σ(0)(1-BT^* 关键词：     

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_100−xV_x samples with 34.4?x?55.1 were investigated by Mössbauer spectroscopy and magnetic measurements in the temperature interval 4.2-300 K. Four magnetic quantities, viz. hyperfine field, Curie temperature, magnetic moment and susceptibility, were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, 〈B〉=12.1 T, average magnetic moment per Fe atom, 〈μ〉=0.89 μ_B, and Curie temperature, T_C=315.3 K. The quantities were shown to be strongly correlated with each other. In particular, T_C is linearly correlated with 〈μ〉 with a slope of 406.5 K/μ_B, as well as 〈B〉 is so correlated with 〈μ〉, yielding 14.3 T/μ_B for the hyperfine coupling constant.     

First-principle study of the structural, electronic, and magnetic properties of amorphous Fe-B alloys

The structural, electronic, and magnetic properties of amorphous Fe_100−xB_x alloys (x=9, 17, 25, 27.3, 33.3, 36.3) are investigated using first-principles calculations. In these amorphous alloys, the short-range order is manifested as a series of Fe- or B-centered polyhedra such as tricapped trigonal prism, icosahedron, and bcc-like structural unit. The electron densities of states of the amorphous alloys resemble those of crystalline Fe borides, which further confirm the similarity of the local order in the amorphous and crystalline phases. All B atoms carry small negative moments of about −0.1μ_B, while small negative moments are also found on very few Fe sites for the Fe-rich compositions (x=9, 17). The average magnetic moment per Fe atom decreases nonlinearly with increasing B composition, which can be associated with the nonlinear relationship between mass density and composition.     

DFT-GGA study of NO adsorption on the LaO (001) surface of LaFeO3

In order to demonstrate the adsorption of the nitrogen monoxide molecule (NO) on the LaO (001) surface of LaFeO₃, we perform simulations based on density functional theory. The generalized gradient approximation (GGA) for the exchange-correlation energy functional indicates that the electronic state of the LaFeO₃ bulk is an anti-ferromagnetic insulator with a local magnetic moment of 4.1 μ_B at each Fe atom. Using the ultrasoft pseudo-potential method with spin-polarized GGA, fully optimized internal parameters as well as charge and spin density are determined for the NO-adsorbed structure prepared in a slab model. The calculated adsorption energy of NO is around ? 1.4 eV on the LaO (001) surface of LaFeO₃. This value decreases down to ? 4.46 eV at an oxygen vacancy site, where the nitrogen atom of NO is embedded in the 1st LaO layer forming a bond with Fe in the 2nd FeO layer.     

Hydrogen induced change of the atomic magnetic moments in Fe/V-superlattices

We have studied the change of the magnetic saturation of (Fe_n/V_m)₃₀ superlattices (30 periods with n monolayers of Fe and m monolayers of V) upon loading with hydrogen using a highly sensitive Faraday balance and in situ loading with hydrogen. We find that the measured magnetic saturation moment for all samples increases with the hydrogen. The measured magnetic saturation moment for all samples increases with the hydrogen concentration. For the superlattice (Fe₃/V₁₁)₃₀ we find the maximum increase, corresponding to a change of the atomic magnetic moments of +0.35 μ_B/Fe atom. We attribute this remarkable effect to a change of the Fe and V magnetic moments at the interfaces caused by the charge transfer from the hydrogen atoms to the vanadium d bands.     

Magnetic and 57Fe Mössbauer studies of collinear spin rotation in Ho2Fe14B

Magnetic properties of Ho₂Fe₁₄B compounds have been studied by the ⁵⁷Fe Mössbauer effect and magnetization measurements. The axes of easy and hard magnetizations lie along the [001] and the [100] directions in the tetragonal structure, respectively, above T_sc = 58 K. From the comparison of the Mössbauer results with the magnetization measurements, it became clear that the Fe and the Ho moments tilt collinearly from the c-axis to the [110] direction throughout the temperature range of 4.2–58 K, and the canting angle reaches to 22° at 4.2 K. The Mössbauer spectra are consistently resolved with six subspectra above T_sc and with twelve below T_sc, together with reasonable site-assignments. We have estimated the mean Ho moment at 10.0μ_B, using the mean Fe moment of 2.3μ_B derived from the average hyperfine field or using the magnetization of Y₂Fe₁₄B as the Fe-sublattice magnetization of Ho₂Fe₁₄B.     

超薄Fe(4?)膜磁特性极化中子反射研究

Ultrathin Fe film 200  V/4  Fe/900  V/MgO（100） has been prepared by molecular beam epitaxy （MBE）. The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity mea 关键词： 超薄Fe膜 磁特性 极化中子反射 分子束外延     

Influence of hydrogen absorption on magnetic properties of Zr(Fe1−xVx)2 ternaries

Measurements of magnetization, susceptibility and Mössbauer effect were made on Zr(Fe_1?xV_x)₂ ternaries and their hydrides. Absorbed hydrogen leads to a large increase (20–30%) in volume without a change in the crystal structure. Ferromagnetism in the Fe-rich region is enhanced by hydrogen absorption, whereas hydrogenation leads to suppression of superconductivity in the V-rich range. The Fe moments in the Zr(Fe_1?xV_x)₂ hydrides are remarkably larger than those in the corresponding host compounds. The Fe moment in the β-ZrFe₂ hydride extrapolated reaches to 2.9μ_B, which exceeds the saturation value in bcc Fe. The hyperfine fields of ⁵⁷Fe in both Zr(Fe_0.8V_0.2)₂ and the hydride distribute widely, indicating that the Fe moments are very sensitive to the local environment arround the Fe atoms. Arguments are presented that it is possible to interprete the Fe moment increase by hydrogenation in terms of a decrease in occupancy of the 3d-band state due to electron transfers from Fe to hydrogen and/or vanadium.     

Adsorption of potassium on iron

Adsorption of K on Fe(110), (100) and (111) surfaces was studied by means of LEED, AES, thermal desorption and work function measurements. The monolayer capacity is about 5.5 × 10¹⁴ K-atoms/cm² in all three cases. With Fe(111) an ordered 3 × 3 overlayer was found at fairly low coverages. The work function decreases to a minimum and the initial dipole moments were determined to μ₀ = 7.0 Debye for Fe(110), μ₀ = 4.4 Debye for K/Fe(100) and μ₀ = 3.9 Debye for K/Fe(111). The heat of adsorption decreases from its initial value (Fe(110): 57; Fe(100): 54; Fe(111): 52 kcal/mole) continuously with increasing coverage which parallels the continuous decrease of the dipole moment of the adsorbate complex.     

Hydrogen absorption and its effect on the magnetic properties of rare-earth iron intermetallics

X-ray diffraction studies of the hydrogen absorption in several YFe and CeFe intermetallic compounds showed that no structural changes occur upon hydrogen absorption in Y₆Fe₂₃, YFe₃, YFe₂. The lattice constants of the hydrides were found to be appreciably larger than those of the pure intermetallic compounds. The magnetic properties of the hydrides were determined and compared with the original compounds. In all cases the magnetic moment per Fe atom proved to be much larger in the hydride phases. Hydrogen absorption can lead to a decrease as well as to an increase of the magnetic ordering temperature (T_c). These changes in T_c could adequately be explained in terms of the observed increases in lattice constant and the data available for the pressure derivative of T_c of these compounds.     

First-principles study on the half-metallicity of zinc-blende CrP(1 1 0) surface

We have investigated the half-metallicity and magnetism at the (1 1 0) surface of CrP by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). From the calculated local density of states (LDOS), we found that the (1 1 0) surface of CrP preserves the half-metallicity, but the band gaps (∼1.1 eV) of the minority states for the surface Cr and P atoms are much reduced from the bulk value (∼1.9 eV). The magnetic moment of the P is coupled antiferromagnetically to that of the Cr. The magnetic moment of surface Cr atom is calculated to be 3.31μ_B which is increased by 10% compared to the bulk value, 3.00μ_B.     

Electronic structure and half-metallicity in Heusler alloys Fe2YB (Y=Ti, V, Mn, Cr)

The electronic structure and magnetic properties of B-based Heusler alloys Fe₂YB (Y=Ti, V, Cr and Mn) have been studied theoretically. These alloys are all ferrimagnets except for Fe₂VB. The latter has 24 valence electrons and is a paramagnetic semimetal. Fe₂CrB is predicted to be half-metals at equilibrium lattice constant. The spin polarization of Fe₂MnB is also quite high. The calculated total moments are 1.00 μ_B for Fe₂CrB and 2.04 μ_B for Fe₂MnB. In Fe₂CrB and Fe₂MnB, the total moments are mainly determined by the partial moment of Cr or Mn. The Fe moment is relatively small and antiparallel to that of Cr or Mn. Under uniform lattice distortion, the half-metallicity of Fe₂CrB is more stable than Fe₂MnB, which is related to the detailed DOS structure of them near E_F.     

Magnetism of single-walled silicon carbide nanotubes doped by boron,nitrogen and oxygen

We calculated, using spin polarized density functional theory, the electronic properties of zigzag (10,0) and armchair (6,6) semiconductor silicon carbide nanotubes (SiCNTs) doped once at the time with boron, nitrogen, and oxygen. We have looked at the two possible scenarios where the guest atom X (B, N, O), replaces the silicon X_Si, or the carbon atom X_C, in the unit cell. We found that in the case of one atom B @ SiCNT replacing a carbon atom position annotated by B_C exhibits a magnetic moment of 1 μ_B/cell in both zigzag and armchair nanotubes. Also, B replacing Si, (B_Si), induce a magnetic moment of 0.46 μ_B/cell in the zigzag (10,0) but no magnetic moment in armchair (6,6). For N substitution; (N_C) and (N_Si) each case induce a magnetic moment of 1 μ_B/cell in armchair (6,6), while N_Si give rise to 0.75 μ_B/cell in zigzag (10,0) and no magnetic moment for N_C. In contrast the case of O_C and O_Si did not produce any net magnetic moment in both zigzag and armchair geometries.     

CEMS interface study of Fe(100)/Pd film structures

The magnetic hyperfine fieldsB _hf near the interface in epitaxial Fe(100)/Pd thin film structures were analyzed using in-situ⁵⁷Fe conversion electron Mössbauer spectroscopy.B _hf is enhanced by about 12% in the 2nd Fe monolayer and approaches the Fe bulk value after a few oscillations within 8–10 Fe monolayers. This oscillating behavior can be described by a superposition of an exponential short-range and an RKKY-like long-range exchange interaction.     

Magnetism in FeAl,CoAl, CoGa and NiAl

Isothermal magnetization vs field data from 1.6 to 300°K for Ni_0.48Al_0.52, Ni_0.50Al_0.50, Co_0.48Al_0.52 and Co_0.50Al_0.50 can be described in terms of contributions from magnetic clusters, from “antistructure” transition metal atoms on Al sites, and from a field- and temperature-independent susceptibility. The moment of antistructure Ni is 0.3μ_B in both nickel alloys. In both cobalt aluminides as well as in Co_0.47Ga_0.53, the antistructure Co moment is 1μ_B. The moment of antistructure Fe in Fe_0.49Al_0.51 is 2.2μ_B.     

The magnetic moment of iron in GdFe intermetallic compounds

Using the multiplet splitting in Fe containing compounds as observed in photoemission the magnetic moment of Fe in GdFe₂, GdFe₃, and Gd₂Fe₁₇ was determined to be (1.76±0.02)μ_B independent of composition. Charge transfer as a cause of this reduction in the Fe moment compared to Fe metal has been excluded. Valence band spectra support a model in which a reduced exchange splitting of the Fe 3d states is responsible for the smaller moment.