Yongquan Guo

Crystal structure and magnetic properties of SmCo5.85Si0.90 compound

The crystal structure and magnetic properties of SmCo7−xSix (x=0.1–0.9) compounds were studied by means of x-ray powder diffraction and magnetic measurements. Rietveld refinement of x-ray powder diffraction pattern shows that the as-cast compound SmCo7−xSix with x=0.9 crystallizes in the TbCu7-type structure with the space group P6/mmm, and the doping element Si has a distinct preference to occupy the 3g site. According to the refinement result, the composition of the compound is derived as SmCo5.85Si0.90. The compound SmCo5.85Si0.90 exhibits ferromagnetic order with the Curie temperature of about 717 K and a saturation moment of about 6.58±0.05 μB/f.u. The SmCo5.85Si0.90 compound shows a strong uniaxial magnetocrystalline anisotropy, and an anomalous increase of magnetization at low temperature is observed in an external field applied perpendicular to the easy direction of magnetization.

Effects of Cu on crystallographic and magnetic properties of Sm(Co,Cu)7

We have investigated the structural stability and magnetic properties of SMCo7-xCu, compounds with the TbCu7-type structure using x-ray powder diffraction and magnetic measurement. A large solid solution with 0.8 less than or equal to x less than or equal to 4.0 in SMCo7-xCux compounds has been observed. Both the lattice parameters and unit cell volume increase with increasing Cu content. SMCo7-xCux compounds exhibit ferromagnetic order. A strong uniaxial magnetocrystalline anisotropy with an anisotropy field as high as 20 T is obtained with x = 0.8 at 5 K. However, the saturation magnetization and Curie temperature decrease with increasing Cu content.

Structure and magnetic properties of La1-xCexFe10.4Si2.6 compounds

The stability, crystal structure and magnetic properties of La1-xCexFe13-ySiy have been investigated by x-ray powder diffraction and magnetic measurements. With increasing Ce content x, the solubility y of the Si and the stability of the NaZn13-type structure decrease. The crystal structure of La0.4Ce0.6Fe10.4Si2.6 was refined by the Rietveld method. The refined result indicates that Si atoms preferentially occupy the 96(i) positions in the NaZn13-type structure. The substitution of Ce for La in LaFe10.4Si2.6 results in a compression of the lattice cell volume and a decrease of the Curie temperature and the saturation magnetization. Taking the free ion value for the moment of the Ce3+ (mu(Ce3+) = 2.1 mu(B)), the moment of the Fe atom was derived according to the antiparallel coupling model. The calculated results indicate that the moment of the Fe atom is weakly dependent on the value of x.

Phase relations in the NdCoSi system at 800°C

Abstract Phase equilibria in the ternary Nd Cs Si system up to a Co:Nd atomic ratio of 2:1 and an Si:Nd atomic ratio of 3:5 were studied by means of X-ray powder diffraction. A total of seven ternary compounds were identified. Among the seven ternary compounds found in this system, the solid solubility of two compounds had not been reported previously: NdCo 13 , Si 4 with 2.5 ⩽ x ⩽ 4 and NdCo 11 , Si 4 with 1.2 ⩽ x ⩽ 1.8. Other new information includes the crystal structure of NdCo 13 , Si 4 . It has a tetragonal structure, related to the NaZn 13 -type, with a = 7.811−7.763A, c = 11.430−11.464A, and the atomic ordering is similar to Ce 2 Ni 17 Si 4 . A limited solid solution range has also been found for Nd 2 Co 17 , Si 4 . This isothermal section consists of 26 three-phase and four two-phase regions.

STRUCTURE AND MAGNETIC-PROPERTIES OF CEFE13-XSIX COMPOUNDS

New iron‐based rare‐earth CeFe13−xSix (2.4≤x≤2.6) intermetallic compounds which crystallized in the NaZn13‐type structure with Fm3c(O6h) space‐group symmetry have been found. The ac susceptibility and the magnetization curve measurements are reported. The substitution of silicon for iron leads to an increase of the Curie temperature and a reduction of the unit‐cell volume. The saturation magnetic moment decreases from 15.7μB/f.u. to 13.4μB/f.u. with x=2.4–2.6.

Crystal structure and magnetic properties of PrCo6.8-xCuxHf0.2 compounds

The effects of Cu substitution on the crystal structure and magnetic properties of PrCo6.8-xCuxHf0.2 (x = 0-1.0) compounds were investigated by means of x-ray powder diffraction and magnetic measurements. The as-cast PrCo6.8-xCuxHf0.2 compounds crystallize in the TbCu7-type structure with the space group P6/mmm. The Curie temperature and magnetic anisotropy field decrease with increasing Cu content. A spin reorientation behaviour has been observed in the PrCo6.8-xCuxHf0.2 compounds. The addition of Cu weakens the anisotropy of the Co sublattice, leading to an increase in the spin reorientation temperature with increasing content of Cu.

The correlation of epitaxial graphene properties and morphology of SiC (0001)

The electronic properties of epitaxial graphene (EG) on SiC (0001) depend sensitively on the surface morphology of SiC substrate. Here, 2–3 layers of graphene were grown on on-axis 6H-SiC with different step densities realized through controlling growth temperature and ambient pressure. We show that epitaxial graphene on SiC (0001) with low step density and straight step edge possesses fewer point defects laying mostly on step edges and higher carrier mobility. A relationship between step density and EG mobility is established. The linear scan of Raman spectra combined with the atomic force microscopy morphology images revealed that the Raman fingerprint peaks are nearly the same on terraces, but shift significantly while cross step edges, suggesting the graphene is not homogeneous in strain and carrier concentration over terraces and step edges of substrates. Thus, control morphology of epitaxial graphene on SiC (0001) is a simple and effective method to pursue optimal route for high quality graphene and...

Anisotropic quantum transport in a network of vertically aligned graphene sheets

Novel anisotropic quantum transport was observed in a network of vertically aligned graphene sheets (VAGSs), which can be regarded as composed of plenty of quasi-parallel, nearly intrinsic, freestanding monolayers of graphene. When a magnetic field was perpendicular to most graphene sheets, magnetoresistance (MR) curves showed a weak localization (WL) effect at low field and a maximum value at a critical field ascribed to diffusive boundary scattering. While the magnetic field was parallel to the graphene sheets, the MR maximum disappeared and exhibited a transition from WL to weak antilocalization (WAL) with increasing temperature and magnetic field. Edges as atomically sharp defects are the main elastic and inelastic intervalley scattering sources, and inelastic scattering is ascribed to electron-electron intervalley scattering in the ballistic regime. This is the first time simultaneously observing WL, WAL and diffusive boundary scattering in such a macroscopic three-dimensional graphene system. These indicate the VAGS network is a robust platform for the study of the intrinsic physical properties of graphene.

Crystal structure and magnetic properties of LaCo10Al3

The crystal structure and magnetic properties of a LaCo10Al3 intermetallic compound have been investigated by x-ray powder diffraction and magnetic measurement. The space group of the LaCo10Al3 structure is I4/mcm, which can be derived from the cubic NaZn13-type structure. Each unit cell contains four formula units of LaCo10Al3. The lattice parameters are a=8.085(1) Angstrom, c=11.624(8) Angstrom, and the calculated density is D-x = 7.07(3) g/cm(3). In each unit cell, there are five kinds of equivalent positions, i.e., 4a, 16l(1), 16k 16l(2), and 4d, which are occupied by 4La, 16Co((1)), 16Co((2)), 1G(Co+Al) and 4Co((3)) atoms, respectively. The tetragonal LaCo10Al3 intermetallic compound is ferromagnetic with a Curie temperature of 840 K. The magnetic moment per Co atom is 0.84 mu(B), which can be explained by the magnetic valence model

Crystallographic and magnetic properties of NdCo11−xSix compounds

The effects of substitution of Si for Co on the crystal structural stability and magnetic properties of NdCo11-xSix compounds have been studied. X-ray diffraction and magnetic measurement show that the single phase region can be expressed as NdCo9.8-9.2Si1.2-1.8 other than NdCo9Si2. X-ray-diffraction study indicates that the compounds adopt the tetragonal BaCd11-type structure. The magnetic properties of a series of NdCo11-xSix solid solutions have been studied by magnetic measurement. Our investigations show that the Curie temperature of NdCo11-xSix increases drastically from 528 K (x=1.8) to 833 K (x=1.2) as the Si content decreases, The Co magnetic moment reaches a maximum between NdCo9.8Si1.2 and NdCo9.6Si1.4, and decreases with the further increase in x. The substitution of Si for Co in NdCo11-xSix leads to a contraction of lattice constant a by 0.2%, c by 0.2%, and a consequent reduction of the unit-cell volume by about 0.6%. The Rietveld refinement results show that the silicon atoms preferentially occupy the 8(d) sites. The occupation of 8(d) sites by proper amount of Si will shift the Fermi level E(F) upward and to a valley with a lower local density of states in NdCo11-xSix compounds, which is favorable for the stability of the BaCd11-type structure