Electronic and vibrational Raman spectroscopy of Nd0.5Sr0.5MnO3 through the phase transitions

Raman scattering experiments have been carried out on single crystals of Nd_0.5Sr_0.5MnO₃ as a function of temperature in the range of 320–50 K, covering the paramagnetic insulator-ferromagnetic metal transition at 250 K and the charge-ordering antiferromagnetic transition at 150 K. The diffusive electronic Raman scattering response is seen in the paramagnetic phase which continue to exist even in the ferromagnetic phase, eventually disappearing below 150 K. We understand the existence of diffusive response in the ferromagnetic phase to the coexistence of the different electronic phases. The frequency and linewidth of the phonons across the transitions show significant changes, which cannot be accounted for only by anharmonic interactions.     

A Brillouin study of the temperature-dependence of the acoustic modes across the insulator-metal transitions in V2O3 and Cr-doped V2O3

Brillouin scattering studies have been carried out on high-quality single crystals of undoped and 0.9% Cr-doped V₂O₃. The observed modes in both the samples at ∼12 and ∼60 GHz are associated with the surface Rayleigh wave (SRW) and bulk acoustic wave (BAW), respectively. In the undoped sample, the mode frequencies of the SRW and BAW modes decrease as the temperature is lowered from room temperature to the insulator-metal transition temperature (T_IM=T_N=∼130 K). Below the transition, the modes show hardening. In the doped sample, the SRW mode shows a similar temperature-dependence as the undoped one, but the BAW mode shows hardening from room temperature down to the lowest temperature (50 K). This is the first measurement of the sound velocity below T_IM in the V₂O₃ system. The softening of the SRW frequency from 330 K to T_IM can be qualitatively understood on the basis of the temperature-dependence of C₄₄, which, in turn, is related to the orbital fluctuations in the paramagnetic metallic phase. The hardening of the mode frequencies below T_IM suggests that C₄₄ must increase in the antiferromagnetic insulating phase, possibly due to the orbital ordering.     

Characterization of isomers of the nucleus154Pm

Consideration of the expected two-quasiparticle structures and their estimated band head energies, and the selection rules for beta transition rates for the¹⁵⁴Nd →¹⁵⁴Pm →¹⁵⁴Sm decays are used to deduce the configurations for the isomers and the low-spin structures in the neutron rich doubly odd nucleus ₆₁ ¹⁵⁴ Pm₉₃. The 2.68 m high spin isomer and the 1.73 m low spin isomer are respectively assigned the spin-parity 4⁺ and 1⁺ with the configuration {p:5/2⁻ [532↑] +n:3/2⁻ [521↑]} with the 2.68 m isomer lying lower in energy, and thus forming the¹⁵⁴Pm ground state. Two-quasiparticle character of the beta-connected states in¹⁵⁴Nd decay and¹⁵⁴Pm decay is discussed.     

Microscopic structures of parity doublets in the151Pm,153Eu and155Eu nuclei

Microscopic structures of the proposed parity doublet bands in the odd-proton Z=61¹⁵¹Pm and Z=63^{153, 155}Eu nuclei are examined using the quasiparticle phonon nuclear model Hamiltonian including the residual pairing and multipole-multipole interactions. Octupole correlations between intrinsic nonrotational states are studied to check the suggested assignments of parity doublet partners in these nuclei. We conclude significant octupole correlations between a pair ofK ^π = 1/2^± doublets in each of these nuclei, with somewhat weaker correlations betweenK ^π = 3/2^± bands in both the Eu isotopes. No octupole connection between the lowestK ^π = 5/2^± bands is found; however, significant octupole collectivity, built on the low-lying 5/2^? bands, is predicted in the higher-lying 5/2⁺ bands which contain the 5/2⁺ [402] fragmented strength.     

Do we need “mock” diquoniums to explain narrow widths into BB channels?

Baryon-antibaryon widths of the “true” diquoniums are calculated using the quark-pair-creation model, otherwise very successful for the decays of ordinary baryons and mesons. The resulting widths are one order of magnitude smaller than generally believed. Combined with an earlier study of diquonium decays into mesonic channels, this would avoid the need for “mock” configurations and make it difficult to interpret structures with widths ≈ 100 MeV as diquoniums.     

The development of information storage materials — How microscopy can help?

The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.     

Peak effect studies in single crystals CeRu2 and 2H-NbS2

We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu₂ and 2H-NbS₂. 2H-NbS₂ is iso-structural and iso-electronic to 2H-NbSe₂, whose similarity with CeRu₂ as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We report on the step change in equilibrium magnetization across the peak effect in CeRu₂. We also present the vortex phase diagram of 2H-NbS₂ obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS₂ and 2H-NbSe₂.