μSR on an induced‐moment spin glass system: Hg1-xFexSe

Zero and longitudinal field μSR have been used to examine the singlet ground state magnetism of the diluted magnetic semiconductor Hg_1-xFe_xSe. For x\geq 0.05\ μSR experiments indicate spin glass behaviour which is limited to sample regions with locally enhanced Fe²⁺ content. Longitudinal field spectra in the glassy state reveal a static local field \sim 50 mT due to induced moments of Fe²⁺. These are proposed to originate from a distribution of bound magnetic polaron energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Valence fluctuations in ternary europium compounds

We outline the possibility to study europium valence fluctuations with the μSR method and report on μSR experiments on the intermetallic compounds EuPdAs and NdPdAs. Above a magnetic transition at 15 K the temperature dependence of the relaxation rate in the trivalent neodymium system behaves like a typical localized moment system. In the valence fluctuating europium compound the zero field relaxation rate levels off at 1.0\ μs^-1 above 40 K. Furthermore, the relaxation enhancement in transverse field experiments is much smaller than expected for a pure dipolar coupling. Therefore an isotropic hyperfine coupling of typical strength is assumed and a valence fluctuation rate of 0.8 μs^-1 at 200 K is derived. Below the magnetic transition at 5 K a disordered spin freezing is concluded in EuPdAs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Raman scattering from three phases in LiIO3

We studied the temperature dependence of the Raman spectrum of LiIO₃, from room temperature up to t ～ 350°C. Two discontinuous changes in the spectrum are observed as temperature increases. The first one is reversible and occurs in a temperature range between 215°C and 260°C, depending upon sample origin (single crystal or powder) and thermal history. The second occurs at t ? 290°C and becomes irreversible once the samples are heated above 340°C. Each phase has a characteristic spectrum, distinct from that of the other two. Although the occurence of these phase changes are in complete agreement with studies made with X-ray diffraction and differential thermal analysis (DTA), it is at variance with previous Raman and infrared work which report no qualitative change in spectrum at the α ? γ phase transition. We believe this disagreement comes about because our measurements are the first ones so far to have actually passed through the transition.     

Pressure dependence of the Raman modes of LiIO3

The pressure dependence of the Raman modes of LiIO₃ at room temperature was studied up to 78 kbar in a gasketed sapphire-anvil cell. Nonlinear frequency increases were observed in all modes involving translation of the light Li⁺ atom. This behavior is more marked in the lowest frequency A mode, which involves translations along the c-axis. Other modes slow smaller linear frequency increases, with increasing pressure. The TO-LO splittings of all but the highest frequency modes are seen to be independent of pressure. This indicates that charge transfer between ions is negligible. For modes derived from internal vibrations of IO₃^- ions an increase in this splitting with increasing pressure is observed, indicating some intra-ion redistribution of charge. Mode Grüneissen parameters are obtained for representative modes of all allowed symmetries in each of the three frequency ranges in which the Raman spectrum of the material can be divided.     

μ+SR on ( La_1.85-x Ndx) Sr0.15 CuO_4

Below 30 K, magnetic order was found in La_1.85-x Nd_x Sr_0.15 CuO_4 with x ranging between 0.30 and 0.60. This order occurs in the low temperature tetragonal phase. Below 5 K, the interaction of Nd and Cu moments modifies the magnetic order in the Cu–O planes leading to an increase of the muon spin rotation frequency and the transverse damping rate. Even down to 0.1 K, considerable spin dynamics is observable. This revised version was published online in August 2006 with corrections to the Cover Date.     

Polarons in organic conjugated polymers

An unified treatment of the electronic structure of organic conjugated polymers based on a renormalization approach is presented. The changes in the electronic structures of trans-polyacetylene, poly-(p-phenylene), polypyrrole and polythiophene, brought about by the presence of polarons in these systems, are studied. For all systems, two localized states, which can be interpreted as the symmetric and antisymmetric combinations of soliton wavefunctions, are created at the central gap.     

Level structures of 95,97Mo — A comparative study

High-spin states of ^95,97Mo (Z=42, N=53,55) nuclei have been investigated through ⁸²Se(¹⁸O, xn) reaction at Eb=60 MeV. The level scheme in ⁹⁵Mo has been observed upto ≏ 10 MeV in the present experiment. The level structure shows mainly single particle character. In ⁹⁷Mo, the ground state level sequence has been extended to ≏ 4.5 MeV while the previous information had been up to 2.4 MeV. A negative parity band built on 1437 keV (11/2⁻) excited state has been extended to 5.5 MeV. The structure seems to show a coexistence of single particle and collective modes of excitation. Properties of both the nuclei have been compared with shell model calculations using OXBASH.     

High spin rotational bands in 65Zn

The nucleus ₃₀ ⁶⁵ Zn was studied using the ⁵²Cr(¹⁶O, 2pn)⁶⁵Zn reaction at a beam energy of 65 MeV. The level scheme is extended up to an excitation energy of 10.57 MeV for spin-parity (41/2?) with several newly observed transitions placed in it.     

Strong Convergence in Hilbert Spaces via Γ-Duality

We analyze a primal-dual pair of problems generated via a duality theory introduced by Svaiter. We propose a general algorithm and study its convergence properties. The focus is a general primal-dual principle for strong convergence of some classes of algorithms. In particular, we give a different viewpoint for the weak-to-strong principle of Bauschke and Combettes and unify many results concerning weak and strong convergence of subgradient type methods.