Synthesis, Electrical and Magnetic Properties of Fe304 Doped by Dy^3＋

The Dy^3＋ -doped Fe3O4 samples were synthesized by sol-gel method, and the effects of dopant on the electrical and magnetic properties were investigated. According to XRD analysis, the high concentration doping of dysprosium ions in Fe3O4 can not be obtained due to the difference of ionic radius, and Fe^3 ＋ ions are replaced by only a small amount of dysprosium ions. The magnetic property was characterized by VSM. The substitution results in the change of saturation magnetization, which may be due to the complex effects of increasing magnetization resulted from Dy^3＋ substitution and decreasing magnetization resulted from the impurity. The electrical property was characterized by four-probe method. With the increasing eoped content, magnetoresistance also increases, then decreases, and increases again. The spin-polarization of doped samples is lower than that of Fe3O4. Lower spin-polarization results in lower tunneling magnetoresistance. Fortunately, barrier was obtained by the second phase at the same time when sample was synthesized. The increase of appropriate barrier height leads to the change of tunneling magnetoresistance.

First Principle Study on the Magnetic and Electric Properties of Wurtzite Cr-phosphides and Cr-sulphides： Several Half-metallic Ferromagnets

The geometrical structures of wurtzite CrX （X=As, Sb, O, Se, and Te） were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%. The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr- phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a1g^2↑↓t1u^4↑↓t1u^1↑↓eg^2↑↓in Cr-phosphides and a1g^2↑↓t1u^4↑↓t1u^1↑t2g^3↑in Cr-sulphides, respectively.

First-principles research on influence of C dopants on magnetic and electric properties of rocksalt MgS

The 2×2× 1 rocksalt C-doped MgS supercells are optimized and their magnetic and electric properties, including the half-metallicity, the conductivity and the supercell magnetic moments, are calculated or analysed by the first- principles researches based on the density functional theory. Results show that the concentration of C-dopants may cause important influence on the magnetic and the electric properties of rocksalt MgS. C dopants are inclined to have a scattering distribution. MGC0.0625S0.9375^, aMgC0.1250S0.8750 and MgC0.1875S0.8125 have evident half-metallicity. They have wide spin energy gaps, thus high Curie temperature possibly. Their supercell magnetic moments are near to integral numbers 2.0, 4.0 and 6.0μB. The main reason for spin polarization and half-metallicity of C-doped MgS is that there are sp hybridized orbitals in ligand compound ML6 caused by covalent interaction between C-ions and Mg-ions.

Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations

s The geometrical structures of Cd0.75TM0.25Se （TM = Ti, V, Cr and Mn） are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange-correlation function based on density functional theory. Cd0.75TM0.25Se （TM =Ti and V） are found to have high spin-polarization near 100% at the Fermi level. Cd0.75TM0.25Se （TM = Cr and Mn） are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely ＋100%. The supercell magnetic moments of Cd0.75Cr0.25Se and Cdo.75Mno.25Se are 4.00 and 5.00 μB, which arise mainly from Cr-ions and Mnions, respectively. The half-metallicity of Cdo.75Cro.25Se is more stable than that of Cd0.75Mn0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr eg2↑t22g↑ and Mn e2 3 ↑t23g↑, respectively.

FERROFLUID CONTAINING SOLUBLE CONDUCTIVE POLYANILINE AND ITS FREESTANDING FILMS

Ferrofluid containing highly conductive polyaniline (PANI) was prepared, in which soluble PANI solutions dopedwith 10-camphorsulfonic acid (CSA) and dodecyl benzenesulfonic acid (DBSA) were used as the basic solution and Fe_3O_4nanoparticles (d = 10 nm) as the magnetic material. Moreover, the freestanding films of the resulting ferrofluid can beobtained by an evaporation method. The electrical and magnetic properties of the ferrofluid or its films can be adjustedthrough changing the content of PANI and Fe_3O_4. High saturated magnetization (≈ 30 emu/g) and high conductivity(≈ 250 S/cm) of the composite films can be achieved when the composite film contains 26.6 wt% of Fe_3O_4. In particular, itwas found that the composite films exhibit a super-paramagnetic behavior (Hc = 0) attributed to the size of Fe_3O_4 particles on the nanometer scale.

Dielectric and Electromagnetic Wave Absorbing Properties of Two Types of SiC Fibres with Different Compositions

The dielectric and electromagnetic properties of two types of SiC fibres with different compositions were investigated. The permittivity and electromagnetic shielding effectiveness （SE） of SiC fibre bundles were measured in 8.2-12.4 GHz by waveguide method. The reflection coefficient （RC） of unidirectional SiC fibre laminates was determined in 8-18 GHz using naval research laboratory （NRL）-arc method. Results showed that the electromagnetic wave （EMW） absorbing properties of SiC fibres were correlated with their composition, microstructure and instinct performance of electrical resistance. SiC fibres with higher content and greater size of nano-scale H-SiC showed higher permittivity, conductivity, SE and lower RC, which resulted in their better EMW absorbing ability, Le. the lower reflection to EMW.

First-Principle Calculations of the MgYA_4(A=Co and Ni)Phase with AuBe_5-Type Structure

First-principles calculations have been performed to study the structural, mechanical and magnetic properties of the MgYCo4 and MgYNi4 phases in AuBes-type structure. The obtained values of cohesive energy as well as formation energy prove that the MgYCo4 and MgYNi4 phases have a good combination of structural stability and alloying ability, which is also supported by electronic structure. It is found that the magnetic moment of the MgYCo4 phase is 19.06 ktB per unit cell mainly owed to the 3d state of Co atom, and the MgYNi4 phase exhibits no magnetism. Both the trigonal shear constant C44 and the shear modulus G of the MgYNi4 phase are larger than those of the MgYCo4 phase. Plasticity of alloys has been estimated by the C11-C12 and Young＇s modulus E, and C12-C44, shear to bulk modulus ratio G/B and Poisson＇s ratio v have been studied to predict the ductility of alloys. According to the calculated results, the MgYCo4 phase has better plasticity as well as ductility, compared with the MgYNi4 phase.