连续波锁模Pr3+:YLF激光器

本文报导了采用氩离子激光器来泵浦Pr³⁺:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转.     

Spin-reorientations in DyFe10Cr2: A57Fe Mössbauer study

We have used⁵⁷Fe Mössbauer spectroscopy carried out on a magnetically aligned powder sample of DyFe₁₀Cr₂ to investigate its magnetic structure at low temperatures. Previous susceptibility measurements by Stefanski [1] demonstrated the occurrence of a spin-reorientation in DyFe₁₀Cr₂ at 190 K. Subsequent work by Yang et al. [2] confirmed this reorientation, at 175 K, and also demonstrated a second spin-reorientation at 75 K. By invoking the example of the RFe₁₁Ti series of compounds, Yang et al. claimed that the reorientation at 175 K is axis-cone type and the 75 K reorientation is cone-plane type. Our measurements confirm the nature of these reorientations.     

<Superscript>57</Superscript>Fe Mössbauer study of the chainpur meteorite

The Chainpur meteorite is one of 23 ordinary chondrites classified as LL3-type (low-Fe & low-metal). It was observed as a shower of stones falling on May 9, 1907 in Uttar Pradesh, India. We report here the characterization of the Fe-bearing phases in this chondrite using ⁵⁷Fe Mössbauer spectroscopy carried out at 298 K, 120 K, 50 K and 13 K. The paramagnetic doublets of olivine and pyroxene dominate the room temperature spectrum, accounting for around 70 % of the spectral area. Moreover, a doublet present with a spectral area of 5 % and assigned to a superparamagnetic Fe ³⁺ phase is a consequence of terrestrial weathering. On the basis of the measured ⁵⁷Fe electric quadrupole splitting of the olivine component at room temperature we estimate the mean Fe:Mg ratio in this meteoritic olivine to be around 35:65 % although there is clearly a wide range of composition. The effects of magnetic ordering of the major components olivine and pyroxene are observed at 13 K.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

155Gd Mössbauer investigation of the magnetic order and spin-reorientation in Gd3Ag4Sn4

In a recent study of the magnetic order in Gd₃Ag₄Sn₄ by neutron powder diffraction and ¹¹⁹Sn Mössbauer Spectroscopy we showed that both the Gd(2d) and Gd(4e) sublattices order antiferromagnetically at 28.8(2) K. We also demonstrated that the ‘magnetic event’ around 8 K is in fact a ‘plane to axis’ spin-reorientation of the Gd magnetic structure. Here, we extend our study with ¹⁵⁵Gd Mössbauer Spectroscopy. The initial magnetic ordering at 30(2) K is clear for both sites and substantial changes in the hyperfine fields are observed at 8 K when the magnetic structure reorients.     

Novel ternary iron-rich,rare-earth iron silicides: R3(Fe1−x Si x )22 (x ∼ 0.16)

In our search for new ternary rare-earth (R) iron silicon intermetallic compounds, a novel ternary phase with the chemical formula R₃Fe_18.5Si_3.5 has been identified with the RFeSi ratio in the range of 12–1574–7810–12. We have studied compounds with R=Gd, Tb, Dy, Ho, Er, Tm and Lu. All of the samples, except for R=Lu, form the new ternary phase3–22. X-ray diffraction data suggest that for R=Gd and Tb, the crystal structure is the rhombohedral Th₂Zn₁₇-type structure and for R=Dy, Ho, Er and Tm, the hexagonal Th₂Ni₁₇-type structure. We suggest that a 1/4 replacement of the R sites by Fe(Si) dumbbells in the CaCu₅-type structure leads to the new3–22 phase, which is an ordered version of the TbCu₇-type structure.⁵⁷Fe Mössbauer spectroscopy has been used to determine the hyperfine parameters of the⁵⁷Fe nuclei in the3–22 compounds. At 295 K, the average hyperfine field of the new3–22 phase ranges from 19.8 T (R=Ho) to 22.2 T (R=Gd). Thermogravimetric analysis (TGA) of these compounds gives Curie temperatures in the range 467 K (Tm)–549 K (Gd). Furthermore, our Mössbauer analysis enables us to investigate the preferential site occupancy shown by Si in these structures.