Electronic structure and magnetic properties of metastable SmCo_7 compound

1 Introduction The rare-earth transition-metal intermetallic compounds have been widely investi-gated for many years, among them the Sm-Co series compounds with 1:5 and 2:17 crys-tal structures. These compounds have been used as sintered and bonded permanent magnets since the 1960s[1,2]. Interest recently has been focused on the TbCu7-type struc-ture Sm-Co intermetallic compounds with a strong uniaxial magnetocrytalline anisot-ropy and a low temperature coefficient (β = ?0.11%)[3―6] due t…     

Electronic structure and magnetic properties of （Mn,N）-codoped ZnO

The electronic structures and magnetic properties of（Mn, N）-codoped Zn O are investigated by using the firstprinciples calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn^2＋ion transfers to the N^2-ion, which leads to the high-state Mn ions（close to ＋2.5）and trivalent N3-ions. In an antiferromagnetic state, one electron transfers to the N2-ion from the downspin Mn2＋ion,while no electron transfer occurs for the upspin Mn^2＋ion. The（Mn, N）-codoped Zn O system shows ferromagnetism,which is attributed to the hybridization between Mn 3d and N 2p orbitals.     

Electronic structure and magnetic susceptibility of monoclinic α-plutonium

The electronic structure of the α-phase of plutonium has been calculated by the band methods with allowance for the spin-orbit interaction and Coulomb correlations in the complete matrix form (the LDA + U + SO method). The strong spin-orbit interaction of the 5 f electrons is manifested in the splitting of the calculated density of the 5f states, which makes a small contribution at the Fermi level on the order of the contribution from the 6d states. Using the results of the ab initio calculations, the spin and orbit contributions to the magnetic susceptibility of α-plutonium have been determined. Along with the impurity contribution, they describe well the experimental data on the susceptibility of this plutonium phase to a temperature of 300 K.     

Effect of Ni deficit on the electronic structure and magnetic properties of PrNi2−xSb2

The influence of a Ni deficit in the nickel sublattice on the electronic and magnetic properties of PrNi_2−xSb₂ compound is investigated. The band structure is calculated using the LMTO method for x=0, 0.50, 1.0 and 1.5. At T=0 K the compound is antiferromagnetic with a magnetic moment on Pr close to 2.0 μ_B.     

Structural,electronic and magnetic properties of the Mn-Ni(110) c(2×2) surface alloy

<正>Using first-principles total energy method,we study the structural,the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy.Paramagnetic,ferromagnetic,and antiferromagnetic surfaces in the top layer and the second layer are considered.It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases.The buckling of the Mn-Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26 A(1 A=0.1 nm) and the weak rippling is 0.038 A in the third layer,in excellent agreement with experimental results.It is proved that the magnetism of Mn can stabilize this surface alloy.Electronic structures show a large magnetic splitting for the Mn atom,which is slightly higher than that of Mn-Ni(100) c(2×2) surface alloy(3.41 eV) due to the higher magnetic moment.A large magnetic moment for the Mn atom is predicted to be 3.81μB.We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate,which confirms the experimental results.The magnetism of Mn is identified as the driving force of the large buckling and the work-function change.The comparison with the other magnetic surface alloys is also presented and some trends are predicted.     

Electronic structure and magnetic and electromagnetic wave absorption properties of BaFe12-xCoxO19 M-type hexaferrites

Crystal, electronic structures and the magnetic and electromagnetic wave absorption properties of BaFe_12-xCo_xO₁₉ (x = 0–2) M-type hexaferrites prepared by a co-precipitation technique were studied. The analyses of X-ray diffraction patterns indicated that the samples mainly crystallized in the P6₃/mmc hexagonal structure, with the additional constitution of Y-type hexaferrite as x > 0. The replacement of Co²⁺ for Fe³⁺ in BaFe_12-xCo_xO₁₉ changed the lattice constants and caused lattice distortions. Particularly, Co²⁺ doping also reduced magnetization and hard magnetic property of BaFe_12-xCo_xO₁₉. This is ascribed to magnetic moment of Co²⁺ smaller than that of Fe³⁺ and to the decrease of magnetocrystalline anisotropy. Having studied electromagnetic wave absorption properties in the frequency range f = 0.1–18 GHz, we found BaFe_12-xCo_xO₁₉ showing high reflection loss (RL) values at frequencies of 0.1–15 GHz, but fairly low RL values at higher frequencies. These features suggest that BaFe_12-xCo_xO₁₉ can be suitable to electronic devices working at GHz frequencies.     

Effect of Dy-Co on physical and magnetic properties of X-type hexaferrites (Ba2−xDyxCu2Fe28−yCoyO46)

Sol–gel method is used to make a sequence of Barium based “X-type hexagonal ferrite (X-HF)” Ba_2−xDy_xCu₂Fe_28 −yCo_yO₄₆. “X-type hexagonal ferrites” with concentrations of “x = 0.0, 0.02, 0.06, 0.1 and y = 0.0, 0.1, 0.3, 0.5” are taken and the substitution impact of trivalent Dy³⁺ and divalent Co²⁺ is observed on the physical and magnetic properties of X-HFs. The XRD result, the refinement of which is accomplished using CelRef software validates the existence of pure single phase in these ferrites. Morphological structure of the crystal grains is calculated using electron microscopy and it is found that the grain has varying size in the range of 0.75–1.001 mm. FTIR analysis is done with and without the sintering process to examine the changes relevant to the structure and the chemistry of the material and the phases existed in the material. Thermogravimetric analyzer is used to measure the TGA and DSC quantities. All FTIR, DSC, and TGA results show that they are in good harmony with the results outcomes from XRD. “Vibrating sample magnetometer (VSM)” is used to quantify the magnetic properties of the sample under observation. It is observed that with an increase in the concentration of Dy-Co, M_r (Remanence) value decreases this could be reasoned by spin canting effect. The value of coercivity (H_c) changes from 317 to 158 G which follows the inverse relation between grain size and coercivity. The future use of the material may be in the microwave absorption devices.     

Electronic structure and optical properties of III–VI crystals

The polarized spectra of the full set of optical functions of GaS, GaSe, InSe, GaTe, InS, and TlSe crystals are determined in a wide range of fundamental-absorption energies. The ?₂ and -Im?^?1 spectra are decomposed into elementary components. The main parameters of the components were determined and the main features of the spectra and transition components are established. The results obtained are explained on the basis of the theoretical band calculations.     

Electronic structure and optical properties of boron-sulfur symmetric codoping in 4 × 4 graphene systems

The electronic structure and optical properties of boron-doped, sulfur-doped, andboron-sulfur-codoped graphene systems have been studied by using first-principlescalculations. Energy band structure and density of states are presented to describe theelectronic properties. The doping can open the band gap and change the optical propertiesof graphene. For all optical properties of doped graphene systems, parallel(E _∥) polarization and perpendicular(E _⊥) polarization are presented. Theoptical properties under two kinds of polarizations are reflected in the range of peakheight and the change of some extraordinary features.     

Role of Al atom on structural and magnetic properties of β-SiC:Cr

The electronic structure, magnetic properties and also the bonding mechanism of the pure SiC and compounds SiC:Cr and SiC:Cr:Al have been studied using the Quantum SPRESSO Software within the density-functional theory (DFT). β-SiC, which is a nonmagnetic semiconductor, has more applications in industry. For the magnetic property, it is alloyed with transition metal. One of the transition metal is chromium. The calculations showed that its alloy at both Si site and C site (SiC:Cr) changes the physical properties of the host material and contributes in the molecular bond. It is seen that if the Al atom was doped in the compounds, SiC:Cr will produce hole carriers and the magnetic properties will thus increase to the considerable values due to the mediation effect. The magnetic property will create the up and down spin band gap to filter carriers. The charge density distribution illustrates that the Al atom has the atomic behavior in the compounds Sic:Cr:Al and does not contribute in the molecular bond. For comparison, the calculations were performed for the pure β-SiC.     

Beneficial effect of Co substitution on the structure and magnetic properties of mechanically alloyed (Pr,Tb)–Fe–(C,B) magnets

The effect of Co substitution on the structure and magnetic properties of mechanically alloyed Pr₁₄Tb₂Fe_76−xCo_xC₆B₂ and Pr₁₆Fe_76−xCo_xC₆B₂ (x=0–20$x=0–20$) alloys has been studied systematically. The main phase in the alloys is Pr₂Fe₁₄C-type carbide, coexisting with a small amount of α-Fe and rare-earth-rich phases. In addition to the increasing of the Curie temperature of the Pr₂Fe₁₄C-type phase, Co substitution can affect the magnetic properties by adjusting the α-Fe fraction of the alloys. The increase of both coercivity and remanence has been realized in a certain composition range. This increase may be attributed mainly to the enhancement of the effective anisotropy constant _Keff$K_{\mathrm{eff}}$ of the magnets due to the reduced α-Fe fraction with a small Co addition. The highest coercivity _iH_c of 20.3 kOe and the optimum energy product (BH)_max of 10.3 MG Oe have been obtained for the Pr₁₄Tb₂Fe_69.5Co_6.5C₆B₂ alloy.     

Structural, electronic and magnetic properties of the Mnben Ni(110) c(2×2) surface alloy

Using first-principles total energy method, we study the structural, the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy. Paramagnetic, ferromagnetic, and antiferromagnetic surfaces in the top layer and the second layer are considered. It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases. The buckling of the Mn–Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26á(1á=0.1 n13) and the weak rippling is 0.038 AA in the third layer, in excellent agreement with experimental results. It is proved that the magnetism of Mn can stabilize this surface alloy. Electronic structures show a large magnetic splitting for the Mn atom, which is slightly higher than that of Mn–Ni(100) c(2×2) surface alloy (3.41 eV) due to the higher magnetic moment. A large magnetic moment for the Mn atom is predicted to be 3.81 μ_B. We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate, which confirms the experimental results. The magnetism of Mn is identified as the driving force of the large buckling and the work-function change. The comparison with the other magnetic surface alloys is also presented and some trends are predicted.     

Role of electrolyte pH on structural and magnetic properties of Co–Fe films

Co–Fe films were electrodeposited on polycrystalline Titanium substrates from the electrolytes with different pH levels. X-ray diffraction (XRD) was used to study the crystal structure of the films. The XRD patterns showed that the films grown at the pH levels of 3.70 and 3.30 have a mixed phase consisting of face-centred cubic (fcc) and body-centred cubic, while those grown at pH=2.90 have only fcc structure. It was observed that the film composition, by energy dispersive x-ray spectroscopy, contain around 88 at% Co and 12 at% Fe for all films investigated in this study. Morphological observations indicated that all films have grainy structure with the slight change of grain size depending on the electrolyte pH. Magnetoresistance measurements, made at room temperature, showed that all films exhibited anisotropic magnetoresistance, which is affected by the electrolyte pH. From the magnetic measurements made by vibrating sample magnetometer, the saturation magnetization increases as the electrolyte pH decreases. Furthermore, all films have in-plane easy-axis direction of magnetization.     

Influence of silicon and atomic order on the magnetic properties of (Fe80Al20)100– x Si x nanostructured system

Mechanically alloyed (Fe₈₀Al₂₀)_100???x Si _x alloys (with x?=?0, 10, 15 and 20) were prepared by using a high energy planetary ball mill, with milling times of 12, 24 and 36 h. The structural and magnetic study was conducted by X-rays diffraction and Mössbauer spectrometry. The system is nanostructured and presents only the BCC disordered phase, whose lattice parameter remains constant with milling time, and decreases when the Si content increases. We found that lattice contraction is influenced 39% by the iron substitution and 61% by the aluminum substitution, by silicon atoms. The Mössbauer spectra and their respective hyperfine magnetic field distributions show that for every milling time used here, the ferromagnetism decreases when x increases. For samples with x?≥?15 a paramagnetic component appears. From the shape of the magnetic field distributions we stated that the larger ferromagnetic phase observed in the samples alloyed during 24 and 36 h is a consequence of the structural disorder induced by mechanical alloying.