238 research outputs found
Electron paramagnetic resonance of Ce3+ and Nd3+ impurity ions in YBa2Cu3O6.13
The electron paramagnetic resonance (EPR) spectra of Ce3+ and Nd3+ impurity ions in unoriented powders of the YBa2Cu3O6.13 compound are observed and interpreted for the first time. It is demonstrated that, upon long-term storage of the samples at room temperature, the EPR signals of these ions are masked by the spectral line (with the g factor of approximately 2) associated with the intrinsic magnetic centers due to the significant increase in its intensit
Synthesis, crystal structure and chemical stability of the superconductor FeSe_{1-x}
We report on a comparative study of the crystal structure and the magnetic
properties of FeSe1-x (x= 0.00 - 0.15) superconducting samples by neutron
powder diffraction and magnetization measurements. The samples were synthesized
by two different methods: a 'low-temperature' one using powders as a starting
material at T =700 C and a "high-temperature' method using solid pieces of Fe
and Se at T= 1070 C. The effect of a starting (nominal) stoichiometry on the
phase purity of the obtained samples, the superconducting transition
temperature Tc, as well as the chemical instability of FeSe1-x at ambient
conditions were investigated. It was found that in the Fe-Se system a stable
phase exhibiting superconductivity at Tc~8K exists in a narrow range of
selenium concentration (FeSe0.974(2)).Comment: 7 pages, 7 figures, 1 tabl
Effect of light Sr doping on the spin-state transition in LaCoO_3
We present an inelastic neutron scattering study of the low energy
crystal-field excitations in the lightly doped cobalt perovskite
La_0.998Sr_0.002CoO_3. In contrast to the parent compound LaCoO_3 an inelastic
peak at energy transfer ~0.75 meV was found at temperatures below 30 K. This
excitation apparently corresponds to a transition between a ground state
orbital singlet and a higher excited orbital doublet, originating from a
high-spin triplet split by a small trigonal crystal field. Another inelastic
peak at an energy transfer ~0.6 meV was found at intermediate temperatures
starting from T > 30 K. This confirms the presence of a thermally induced
spin-state transition from the low-spin Co^3+ to a magnetic high-spin state in
the non-disturbed LaCoO_3 matrix. We suggest that hole doping of LaCoO_3 leads
to the creation of a magnetic polaron and hence to the low-to-high spin state
transition on the relevant Co sites.Comment: 4 pages, 2 figures; based on a talk given at ICM'06, Kyoto; to appear
in JMM
Phase Diagram of the Dzyaloshinskii-Moriya Helimagnet Ba2CuGe2O7 in Canted Magnetic Fields
The evolution of different magnetic structures of non-centrosymmetric
Ba2CuGe2O7 is systematically studied as function of the orientation of the
magnetic field H. Neutron diffraction in combination with measurements of
magnetization and specific heat show a virtually identical behaviour of the
phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0)
plane. The existence of a recently proposed incommensurate double-k AF-cone
phase is confirmed in a narrow range for H close to the tetragonal c-axis. For
large angles enclosed by H and the c-axis a complexely distorted non-sinusoidal
magnetic structure has recently been observed. We show that its critical field
Hc systematically increases for larger canting. Measurements of magnetic
susceptibility and specific heat finally indicate the existence of an
incommensurate/commensurate transition for H /sim 9 T applied in the basal
(a,b)-plane and agree with a non-planar, distorted cycloidal magnetic
structure.Comment: 14 pages, 13 figure
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