Effect of bismuth on the electrical properties of Pb0.8Sn0.2Te thin films

D.C. conductivity and Hall coefficient studies were made on bismuth doped Pb_0.8Sn_0.2Te thin films in the temperature range 77–300 K. Hall coefficient and Hall mobility are found to decrease with the increase in doping density of bismuth. Films doped with even 0.3 at.% Bi changed fromp-type ton-type due to the donor action of bismuth in these films. Analysis of mobility-temperature data revealed that the lattice and defect scattering mechanisms are predominant in these films. Defect limited mobility is calculated for all the films and it is found to decrease with increase in doping concentration of bismuth suggesting the increase in defect density.     

Pb0.8Sn0.2Te晶体高压相变的X射线衍射研究

 利用X射线粉末衍射方法，在室温高压下观察到了Pb_0.8Sn_0.2Te晶体的压致相变现象。实验是在DAC高压装置上完成的，压力从零逐步加至25.2 GPa。在常温常压下，Pb_0.8Sn_0.2Te具有fcc结构。从实验结果看到，有两个结构相变存在，分别在压力为6.1 GPa和14.9 GPa附近。我们认为，前一个结构相变与Pb_0.8Sn_0.2Te晶体的金属化有密切关系。实验分别从10.0 GPa和25.2 GPa降压至零，发现相变均是可逆的。     

Low-temperature hot-electron energy relaxation in Hg0.8Cd0.2Te in extreme-quantum-limit magnetic fields

Energy relaxation time of hot electrons in Hg_0.8Cd_0.2Te at a lattice temperature of 1.5 K is calculated for quantizing magnetic flux densities of 4 and 6 T considering acoustic scattering via deformation potential and piezoelectric couplings. Band nonparabolicity, nonequipartition of phonons, screening of the scattering rates due to carrier space charge, and low-temperature broadening of the Landau level are incorporated. The calculated results agree qualitatively with experimental data.     

Theory of magnetic susceptibility of the narrow-gap semiconductors Pb(Sn)Te

The nonoscillating singular part of the susceptibility of Pb_1?xSn_xTe alloys is calculated. The dependence on the composition x, temperature and the carrier concetration is explained by the existence of the valence band, separated from the conduction band with a small energy gap.     

Effect of annealing treatment on the magnetic properties of mechanochemical synthesized La0.8Pb0.2MnO3 manganites

In this paper, we have investigated the effect of annealing on structural and magnetic properties of La_0.8Pb_0.2MnO₃ (LPMO) polycrystalline samples. Mechanochemical procedure has been used to produce LPMO nanocrystalline samples from oxide precursors. From the AC susceptibility measurements we found that the magnitude of susceptibility increases and the paramagnetic–ferromagnetic (PM–FM) transition width decreases by annealing the ball milled powders. Also, reentrant spin glass (RSG) behavior has been found in high temperature annealed samples. It seems that, due to the evaporation of PbO in high temperature annealed samples, vacancies created in perovskite structure and portion of the Mn³⁺–O–Mn⁴⁺ network is broken. So the FM double-exchange interaction is weakened due to the magnetic dilution and the antiferromagnetc (AFM) phase fraction increases in high temperature annealed samples. The competition between FM double-exchange interaction and AFM super-exchange interaction produces spin frustration and is responsible for the occurrence of RSG.     

Ferromagnetism of (Pb,Sn, Mn) Te under high pressure

Results of measurements of the magnetic susceptibility in the p-type diluted magnetic semiconductor [(PbTe)_1-x(SnTe)_x]_1-y(MnTe)_y with x = 0.72, y = 0.03 are presented. The temperature of the ferromagnetic ordering T_c increases (for hole concentration 3×10²⁰ cm^-3) < p < 7 × 10²⁰ cm^-3 or decreases (p > 7 × 10²⁰ cm^-3) as hydrostatic pressure is applied. The pressure causes an increase in the concentration of carriers responsible for the interactions between Mn ions. The observed shift of T_c with pressure is interpreted on the basis of the RKKY interaction mechanism and points out the importance of the band structure behavior in consideration of magnetic properties of the semiconductor.     

Anisotropic superconducting properties of FeSe0.5Te0.5 single crystals

We investigated the anisotropic electrical transport and magnetic properties of FeSe$_{0.5}$Te$_{0.5}$ single crystals grown by the self-flux method. The in-plane resistivity shows a metallic-like temperature dependence, while the out-of-plane resistivity shows a broad hump with a maximum at around 64 K. The magnetization loops for $H/\!/c$-axis and $H/\!/ab$-plane are also different, for example, there is a typical second peak for $H/\!/c$-axis. The in-plane critical current density is larger than the out-of-plane one. The coherence length and penetration depth were estimated by the Ginzburg-Landau theory. The anisotropic parameter $\gamma $ depends on the applied magnetic field and the temperature. The coupling of superconducting FeSe(Te) layers and the flux pinning mechanism relevant to anisotropy are also discussed.     

Studying the magnetic properties of CoSi single crystals

The magnetic properties of CoSi single crystals have been measured in a range of temperatures T = 5.5–450 K and magnetic field strengths H ≤ 11 kOe. A comparison of the results for crystals grown in various laboratories allowed the temperature dependence of magnetic susceptibility χ(T) = M(T)/H to be determined for a hypothetical “ideal” (free of magnetic impurities and defects) CoSi crystal. The susceptibility of this ideal crystal in the entire temperature range exhibits a diamagnetic character. The χ(T) value significantly increases in absolute value with decreasing temperature and exhibits saturation at the lowest temperatures studied. For real CoSi crystals of four types, paramagnetic contributions to the susceptibility have been evaluated and nonlinear (with respect to the field) contributions to the magnetization have been separated and taken into account in the calculations of χ(T).     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

利用光学金相显微镜对TEA-CO2脉冲强激光辐照的Hg0.8Cd0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J,能量密度为937.5 J/cm2的强激光辐照下,晶片表面呈现出熔融迹象和大量的微裂纹,微裂纹密度从激光辐照区中心向外逐渐减少,裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加,晶片表面熔融更加剧烈,裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

 利用光学金相显微镜对TEA-CO₂脉冲强激光辐照的Hg_0.8Cd_0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J，能量密度为937.5 J/cm²的强激光辐照下，晶片表面呈现出熔融迹象和大量的微裂纹，微裂纹密度从激光辐照区中心向外逐渐减少，裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加，晶片表面熔融更加剧烈，裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

On the activation energy of the electron liquid in Hg0.8Cd0.2Te

Recently we have shown that a magnetic field induced electron (Wigner) condensation takes places in Hg_0.8Cd_0.2Te. The correlated electrons behave like a viscous liquid with activated mobility [1]. We present the activation energy of the mobility at magnetic fields up to B = 20 T. The experimental data show that the strong increase of the activation energy with B at low fields slow down and even seems to saturate at magnetic fields above 20 T. Qualitatively this behaviour is expected for a magnetic field induced electron liquid.     

Structural and magnetic properties of CeZnAl_3 single crystals

We have synthesized single crystals of CeZnAl_3,which is a new member of family of Ce-based intermetallics CeTX_3(T=transition metal, X=Si, Ge, Al), crystallizing in the non-centrosymmetric tetragonal BaNiSn_3-type structure. Magnetization,specific heat and resistivity measurements all show that CeZnAl_3 orders magnetically below around 4.4 K. Furthermore,magnetization measurements exhibit a hysteresis loop at low temperatures and fields, indicating the presence of a ferromagnetic component in the magnetic state. This points to a different nature of the magnetism in CeZnAl_3 compared to the other isostructural CeTAl_3 compounds. Resistivity measurements under pressures up to 1.8 GPa show a moderate suppression of the ordering temperature with pressure, suggesting that measurements to higher pressures are required to look for quantum critical behavior.     

Effect of Pb on structural and magnetic properties of Ba-hexaferrite

Lead was doped in barium hexaferrite by co-precipitation method and the Pb-doped Ba-hexaferrite with compositions of Ba_1−xPb_xFe₁₂O₁₉ was investigated for the first time at x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0. The molar ratio (Fe³⁺/Ba²⁺) of the solutions was kept 12 while pH was maintained at 13 by using NaOH (M=5) as precipitating agent. Prepared samples were sintered at 965±5 °C for three hours. Structural and morphological studies were done by X-ray diffractometer (XRD) and the scanning electron microscope (SEM). SEM micrographs confirmed the formation of hexagonal plate like structures and particle size was observed to be increased with the increase in Pb concentration. The hysteresis loops obtained from the magnetometer showed that with the increase in Pb concentration, the coercivity decreased while magnetic induction and remanence increased, which in turn increased the maximum energy product (BH)_max. Lower coercivity and the moderate increase in saturation magnetization obtained from Pb doping makes the material useful for magnetic recording media and other frequency based applications.