248 research outputs found
Crystal field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3
Inelastic neutron scattering experiments have been carried out to determine
the crystal field states of the Kondo lattice heavy fermions CeRuSn3 and
CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space
group Pm-3n) in which the Ce atoms occupy two distinct crystallographic sites
with cubic (m-3) and tetragonal (-4m.2) point symmetries. The INS data of
CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV which
is accounted by a model based on crystal electric field (CEF) excitations. On
the other hand, the INS data of isostructural CeRhSn3 reveal three CEF
excitations around 7.0, 12.2 and 37.2 meV. The neutron intensity sum rule
indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3+
state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds
are deduced. We estimate the Kondo temperature T_K = 3.1(2) K for CeRuSn3 from
neutron quasielastic linewidth in excellent agreement with that determined from
the scaling of magnetoresistance which gives T_K = 3.2(1) K. For CeRhSn3 the
neutron quasielastic linewidth gives T_K = 4.6 K. For both CeRuSn3 and CeRhSn3,
the ground state of Ce3+ turns out to be a quartet for the cubic site and a
doublet for the tetragonal site.Comment: 12 pages, 13 figures, 2 tables, to appear in Phys. Rev.
Mechanistic approach of Goss abnormal grain growth in electrical steel: Theory and argument
The first Si-Fe electrical steel was produced in 1905, and the grain-oriented steel was discovered in 1930 after Goss demonstrated how optimal combinations of heat treatment and cold rolling could produce a texture giving Si-Fe strip good magnetic properties when magnetised along its rolling direction. This technology has reduced the power loss in transformers greatly and remains the basis of the manufacturing process today. Since then many postulations reported on the mechanism on abnormal grain growth (AGG) which is the key for Si-Fe superior magnetic properties, however, none have provided a concrete understanding of this phenomenon. Here, we established and demonstrated a new theory that underlines the fundamental mechanistic approach of abnormal grain growth in 3% Si-Fe steel. It is demonstrated, that the external heat flux direction applied during annealing and Si atom positions in the solid solution disordered α-Fe cube unit cell that cause lattice distortions and BCC symmetry reduction are the most influential factors in the early stage of Goss AGG than what was previously thought to be dislocation related stored energy, grain boundary characteristics and grain size/orientation advantages
Physical properties of noncentrosymmetric superconductor LaIrSi3: A {\mu}SR study
The results of heat capacity C_p(T, H) and electrical resistivity \rho(T,H)
measurements down to 0.35 K as well as muon spin relaxation and rotation
(\muSR) measurements on a noncentrosymmetric superconductor LaIrSi3 are
presented. Powder neutron diffraction confirmed the reported noncentrosymmetric
body-centered tetragonal BaNiSn3-type structure (space group I4\,mm) of
LaIrSi3. The bulk superconductivity is observed below T_c = 0.72(1) K. The
intrinsic \Delta C_e/\gamma_n T_c = 1.09(3) is significantly smaller than the
BCS value of 1.43, and this reduction is accounted by the \alpha-model of BCS
superconductivity. The analysis of the superconducting state C_e(T) data by the
single-band \alpha-model indicates a moderately anisotropic order parameter
with the s-wave gap \Delta(0)/k_B T_c = 1.54(2) which is lower than the BCS
value of 1.764. Our estimates of various normal and superconducting state
parameters indicate a weakly coupled electron-phonon driven type-I s-wave
superconductivity in LaIrSi3. The \muSR results also confirm the conventional
type-I superconductivity in LaIrSi3 with a preserved time reversal symmetry and
hence a singlet pairing superconducting ground state.Comment: 11 pages, 8 figures, 2 table
Prompt gamma activation studies on archaeological objects at a pulsed neutron source
The potential of Prompt Gamma Activation Analysis (PGAA) for
non-destructive quantitative investigation of archaeological objects at a pulsed neutron spallation source was studied. Experiments were performed on the ROTAX
time-of-flight diffractometer of the ISIS neutron source on a chalcolithic copper axe, a limestone sample from the ancient Quarry of Masarah (Egypt), a Roman bronze fibula and two fragments of glass from the Roman Villa Adriana. For reference and comparison, measurements were also performed at the PGAA station of the Budapest research reactor. It is found that the performance of a PGAA analysis
at a pulsed source, with a make-shift set-up on an instrument designed for diffraction studies, cannot match the achievable results at a dedicated PGAA facility at a reactor source. However, the possibility of performing different investigations, e.g., neutron diffraction for structure analysis and PGAA for elemental analysis, at a single facility on one and the same object remains attractive and offers useful applications in the field of cultural heritage
Magneto-elastic coupling and competing entropy changes in substituted CoMnSi metamagnets
We use neutron diffraction, magnetometry and low temperature heat capacity to
probe giant magneto-elastic coupling in CoMnSi-based antiferromagnets and to
establish the origin of the entropy change that occurs at the metamagnetic
transition in such compounds. We find a large difference between the electronic
density of states of the antiferromagnetic and high magnetisation states. The
magnetic field-induced entropy change is composed of this contribution and a
significant counteracting lattice component, deduced from the presence of
negative magnetostriction. In calculating the electronic entropy change, we
note the importance of using an accurate model of the electronic density of
states, which here varies rapidly close to the Fermi energy.Comment: 11 pages, 9 figures. Figures 4 and 6 were updated in v2 of this
preprint. In v3, figures 1 and 2 have been updated, while Table II and the
abstract have been extended. In v4, Table I has updated with relevant neutron
diffraction dat
Neutron diffraction study of Bronze Age tools from second millennium BC dwellings in Italy
Neutron diffraction was utilized to characterise XX to XIII century BC bronze axes (Ancient to Late Bronze Age from “Terramare” and other Bronze Age settlements near Modena, Italy. Archaeometric metallurgy issues have been
addressed by means of phase and texture analysis from measurements carried out at the ROTAX and GEM beam lines of the neutron spallation source ISIS of the Rutherford Appleton Laboratory (UK). Neutron data provide accurate composition and structural information from the bulk of the alloy, with good grain statistics, without limitations due to surface alterations and with few limitations as to sample
size. Bronze composition results are in good agreement with data obtained by micro-sampling and traditional analytical techniques thus confirming the validity of the method used for a totally non-destructive determination of the alloy composition from precise lattice parameter measurements. Phase analysis from diffraction profiles provides identification and quantification of surface alteration and corrosion products, free of interference with the analysis of the bulk alloy. Furthermore, texture analysis techniques may yield information on the ancient production methods of the artefacts
Neutron diffraction study of Bronze Age tools from second millennium BC dwellings in Italy
Neutron diffraction was utilized to characterise XX to XIII century BC bronze axes (Ancient to Late Bronze Age from “Terramare” and other Bronze Age settlements near Modena, Italy. Archaeometric metallurgy issues have been
addressed by means of phase and texture analysis from measurements carried out at the ROTAX and GEM beam lines of the neutron spallation source ISIS of the Rutherford Appleton Laboratory (UK). Neutron data provide accurate composition and structural information from the bulk of the alloy, with good grain statistics, without limitations due to surface alterations and with few limitations as to sample
size. Bronze composition results are in good agreement with data obtained by micro-sampling and traditional analytical techniques thus confirming the validity of the method used for a totally non-destructive determination of the alloy composition from precise lattice parameter measurements. Phase analysis from diffraction profiles provides identification and quantification of surface alteration and corrosion products, free of interference with the analysis of the bulk alloy. Furthermore, texture analysis techniques may yield information on the ancient production methods of the artefacts
Neutron diffraction study of Bronze Age tools from second millennium BC dwellings in Italy
Neutron diffraction was utilized to characterise XX to XIII century BC bronze axes (Ancient to Late Bronze Age) from "Terramare" and other Bronze Age settlements near Modena, Italy. Archaeometric metallurgy issues have been addressed by means of phase and texture analysis from measurements carried out at the ROTAX and GEM beam lines of the neutron spallation source ISIS of the Rutherford Appleton Laboratory (UK), Neutron data provide accurate composition and structural information from the bulk of the alloy, with good grain statistics, without limitations due to surface alterations and with few limitations as to sample size. Bronze composition results are in good agreement with data obtained by micro-sampling and traditional analytical techniques thus confirming the validity of the method used for a totally non-destructive determination of the alloy composition from precise lattice parameter measurements. Phase analysis from diffraction profiles provides identification and quantification of surface alteration and corrosion products, free of interference with the analysis of the bulk alloy. Furthermore, texture analysis techniques may yield information on the ancient production methods of the artefacts. © Società Italians di Fisica
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