F. S. Liu

Structure and magnetic properties of Mn-doped ZnO nanoparticles

We report the crystal structure and magnetic properties of the Zn1-xMnxO compounds synthesized by a combustion method. The Zn1-xMnxO compounds with x=0-0.1 crystallize in the wurtzite ZnO structure. The lattice parameters a and c of Zn1-xMnxO increase linearly with the Mn content, indicating that Mn2+ ions substitute for Zn2+ ions. Scanning electron microscopy shows that the average particle radius of Zn0.95Mn0.05O is about 40 nm. From the Curie-Weiss behavior of susceptibility at high temperature, it was found that the Mn-Mn interaction is dominated by antiferromagnetic coupling with effective nearest-neighbor exchange constant J about -32 K and the large negative value of the Curie-Weiss temperature

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.

Crystal structure and magnetic properties of SmCo7-xHfx compounds

The crystal structure and magnetic properties of SmCo7-xHfx (x=0.05,0.1,0.2,0.3) compounds were studied by means of x-ray powder diffraction and magnetic measurements. The as-cast compounds SmCo7-xHfx with x=0.1 and 0.2 crystallize in the TbCu7-type structure with the space group P6/mmm. According to the structure refinement, the doping element Hf prefers to occupy the 2e site. The compounds have high Curie temperatures (1080 K for x=0.1, 1075 K for x=0.2), large saturation magnetization (104 emu/g for x=0.1, 102 emu/g for x=0.2 at 5 K), and large magnetic anisotropy fields (244 kOe for x=0.1, 282 kOe for x=0.2 at 5 K) with strong uniaxial magnetocrystalline anisotropy

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.

Thermoelectric properties of (Zn0.98M0.02)4Sb3 (M = Al, Ga and In) at low temperatures

Thermoelectric properties of substitutional compounds (Zn0.98M0.02)4Sb3 (M = Al, Ga and In) were investigated at temperatures from 5 to 310 K. The results indicate that substitution of M for Zn in Zn4Sb3 leads to a decrease in electrical resistivity ρ, thermopower S and thermal conductivity λ. The decrease in ρ and S of (Zn0.98M0.02)4Sb3 would originate from increased electron contribution caused by introduction of donor levels due to substitution of M3+ for Zn2+. Nevertheless, our experiments revealed that as the dopant changed from Al to Ga and then to In, the resistivity of (Zn0.98M0.02)4Sb3 increased monotonically, which could be caused by reduced mobility due to the increase in the ionic radius from Al to In. Meanwhile, λ of (Zn0.98M0.02)4Sb3 at low temperatures (especially at T 250 K due to the large reduction in its resistivity, indicating that the thermoelectric properties of β-Zn4Sb3 can be enhanced by Al doping.

Visible and infrared emissions from c-axis oriented AlN : Er films grown by magnetron sputtering

Visible and infrared photoluminescence was observed from AlN:Er films grown by reactive radio-frequency magnetron sputtering under different powers. X-ray diffraction indicates that the films have a c-axis oriented hexagonal wurtzite structure with an average crystallite size of about 59-83 nm and a strain of about (1.12-1.69) x 10(-3). Green emissions (similar to 540 and 558 nm) from the AlN: Er films are due to the intra-4f(n) transition of Er3+ from H-2(11/2) and S-4(3/2) to I-4(15/2), and infrared (similar to 1535 nm) emissions correspond to I-4(13/2) to I-4(15/2) transitions. Increasing the sputtering power results in larger grain size, lower strain, and enhancement of the luminescence intensity. (c) 2006 American Institute of Physics.

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.

Structure and visible photoluminescence of Sm3+, Dy3+and Tm3+ doped c-axis oriented AlN films

Visible photoluminescence (PL) has been observed from rare earth (Tm, Sm and Dy)-doped AlN films grown by radio-frequency magnetron reactive sputtering. X-ray diffraction indicates that the films are c-axis- oriented hexagonal wurtzite type structure with an average crystal size of about 80 - 110 nm. Room-temperature PL spectra indicate that the blue emission is due to the transition of D-1(2) to F-3(4) and (1)G(4) to H-3(6) intra 4f electron of Tm3+, the yellow emissions of AlN: Sm are due to (4)G(5/2) to the H-6(J) (J = 5/2, 7/2, 9/2, 11/2) and the reddish emissions of AlN:Dy correspond to the F-4(9/2) to H-6(J) (J = 15/2, 13/2, 11/2 and 9/2) and F-6(11/2) transitions.

Effects of iron substitution on magnetic properties of SmCo6.8-xFexHf0.2 compounds

The effects of iron substitution on the crystal structure and magnetic properties of SrHCo6.8-xFexHf0.2 (x = 0.1, 0.3, 0.5, and 0.7) compounds were investigated by means of x-ray powder diffraction and magnetic measurements. The as-east SMCo6.8-xFexHf0.2 compounds crystallize in the TbCu7-type structure with the space group P6/mmm. The lattice parameters a and c increase with the Fe content. The SMCo6.8-xFexHf0.2 compounds exhibit ferromagnetic order with a strong room temperature uniaxial magnetocrystalline anisotropy. The Curie temperature and saturation magnetization increase with the Fe content. The magnetic anisotropy field of the compounds reaches a maximum value at x = 0.5. The anomalous concentration dependence of the anisotropy field is explained by considering the contribution of individual site anisotropy in combination with the preferential occupation of 3d ions on different sites.

Enhancement of superconducting transition temperature via Ba doping in RuSr2-xBaxGdCu2O8 (x <= 0.1)

The crystal structure and superconducting properties of RuSr2−xBaxGdCu2O8 (0⩽x⩽0.1) have been investigated. X-ray powder diffraction (XRD) patterns show that the solid solution range is 0⩽x⩽0.1. The superconducting transition temperature was raised up to 35 K (zero) and 62 K (onset) for x=0.07, from 16 K (zero) and 45 K (onset) for x=0.0, and then TC decreases with x when x>0.07. Rietveld refinement for XRD data of RuSr2−xBaxGdCu2O8 show that the apical Cu–O(1) bond length increases with an increase of x, while the Ru–O(1) bond length decreases, This may account for the enhancement of the superconducting transition temperature.