1,367 research outputs found
Electrical and magnetic properties of the complete solid solution series between SrRuO3 and LaRhO3: Filling t2g versus tilting
A complete solid solution series between the t2g^4 perovskite ferromagnet
SrRuO3 and the diamagnetic t2g^6 perovskite LaRhO3 has been prepared. The
evolution with composition x in (SrRuO3)(1-x)(LaRhO3)(x) of the crystal
structure and electrical and magnetic properties has been studied and is
reported here. As x increases, the octahedral tilt angle gradually increases,
along with the pseudocubic lattice parameter and unit cell volume. Electrical
resistivity measurements reveal a compositionally driven metal to insulator
transition between x = 0.1 and 0.2. Ferromagnetic ordering gives over to glassy
magnetism for x > 0.3 and no magnetic ordering is found above 2 K for x > 0.5.
M_sat and Theta_CW decrease with increasing x and remain constant after x =
0.5. The magnetism appears poised between localized and itinerant behavior, and
becomes more localized with increasing x as evidenced by the evolution of the
Rhodes-Wohlfarth ratio. mu_eff per Ru is equal to the quenched spin-only S
value across the entire solid solution. Comparisons with Sr(1-x)Ca(x)RuO3
reinforce the important role of structural distortions in determining magnetic
ground state. It is suggested that electrical transport and magnetic properties
are not strongly coupled in this system
Raman response of Stage-1 graphite intercalation compounds revisited
We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6
graphite intercalation compounds (GIC) to unravel their intrinsic finger print.
Four main components were found between 1200 cm-1 and 1700 cm-1, and each of
them were assigned to a corresponding vibrational mode. From a detailed line
shape analysis of the intrinsic Fano-lines of the G- and D-line response we
precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and
asymmetry (q) from each component. The comparison to the theoretical calculated
line width and position of each component allow us to extract the
electron-phonon coupling constant of these compounds. A coupling constant
{\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone
are not sufficient to explain the superconductivity within the electron-phonon
coupling mechanism in CaC6 and KC8.Comment: 6 pages, 3 figures, 2 table
Kinetics and mechanism of the formation of manganese(III) from manganese(II) and (VII) in aqueous perchlorate solution
The reaction 4MnIIfMnVxI = 5MnIII obeyed the rate equation, rate = k[Mnu]2[MnvII]. In lithium perchlorate media the [H+]-dependence was found to be k = k~H+]+ko. Activation energies and entropies were compared with standard values for formation of intermediate species in an examination of possible mechanisms
Kinetics of the aqueous manganese(III)+ iron(II) reaction by platinum-electrode polarography
The rate equation âd[FeII]/dt=kobs[FeII][MnIII] was established by measurements of the iron(II) diffusion current. For 0.3â15°C in 0.54-3 M HClO4 the variation of kobs was consistent with the relation kobs=(ko[H+]+k1Kh)/([H+]+Kh), where Kh is the manganese(III) hydrolysis constant. Values of k0 are just less than k1 as in the comparable oxidation of vanadium(IV). It is concluded from further comparisons of rates that the activated complexes are outer-sphere
The effect of Mg location on Co-Mg-Ru/Îł-Al2O3 FischerâTropsch catalysts
© 2016 The Author(s) Published by the Royal Society. All rights reserved.The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer-Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3-xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3-xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3-xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-Time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature
Two-electronic component behavior in the multiband FeSeTe superconductor
We report X-band EPR and Te and Se NMR measurements on
single-crystalline superconducting FeSeTe ( = 11.5(1)
K). The data provide evidence for the coexistence of intrinsic localized and
itinerant electronic states. In the normal state, localized moments couple to
itinerant electrons in the Fe(Se,Te) layers and affect the local spin
susceptibility and spin fluctuations. Below , spin fluctuations become
rapidly suppressed and an unconventional superconducting state emerges in which
is reduced at a much faster rate than expected for conventional - or
-wave symmetry. We suggest that the localized states arise from the
strong electronic correlations within one of the Fe-derived bands. The
multiband electronic structure together with the electronic correlations thus
determine the normal and superconducting states of the FeSeTe
family, which appears much closer to other high- superconductors than
previously anticipated.Comment: 5 pages, 4 figure
Jahn-Teller orbital glass state in the expanded fcc Cs3C60 fulleride
The most expanded fcc-structured alkali fulleride, Cs3C60, is a Mott insulator at ambient pressure because of the weak overlap between the frontier t1u molecular orbitals of the C603â anions. It has a severely disordered antiferromagnetic ground state that becomes a superconductor with a high critical temperature, Tc of 35 K upon compression. The effect of the localised t1u3 electronic configuration on the properties of the material is not well-understood. Here we study the relationship between the intrinsic crystallographic C603â orientational disorder and the molecular JahnâTeller (JT) effect dynamics in the Mott insulating state. The high-resolution 13C magic-angle-spinning (MAS) NMR spectrum at room temperature comprises three peaks in the intensity ratio 1:2:2 consistent with the presence of three crystallographically-inequivalent carbon sites in the fcc unit cell and revealing that the JT-effect dynamics are fast on the NMR time-scale of 10â5 s despite the presence of the frozen-in C603â merohedral disorder disclosed by the 133Cs MAS NMR fine splitting of the tetrahedral and octahedral 133Cs resonances. Cooling to sub-liquid-nitrogen temperatures leads to severe broadening of both the 13C and 133Cs MAS NMR multiplets, which provides the signature of an increased number of inequivalent 13C and 133Cs sites. This is attributed to the freezing out of the C603â JT dynamics and the development of a t1u electronic orbital glass state guided by the merohedral disorder of the fcc structure. The observation of the dynamic and static JT effect in the Mott insulating state of the metrically cubic but merohedrally disordered Cs3C60 fulleride in different temperature ranges reveals the intimate relation between charge localization, magnetic ground state, lifting of electronic degeneracy, and orientational disorder in these strongly-correlated systems
Spin frustration and magnetic ordering in theS=12molecular antiferromagnetfccâCs3C60
We have investigated the low-temperature magnetic state of face-centered-cubic (fcc) Cs3C60, a Mott insulator and the first molecular analog of a geometrically frustrated Heisenberg fcc antiferromagnet with S=1/2 spins. Specific heat studies reveal the presence of both long-range antiferromagnetic ordering and a magnetically disordered state below TN=2.2 K, which is in agreement with local probe experiments. These results together with the strongly suppressed TN are unexpected for conventional atom-based fcc antiferromagnets, implying that the fulleride molecular degrees of freedom give rise to the unique magnetic ground state
Detection and Crystal Structure of Hydrogenated Bipentacene as an Intermediate in Thermally Induced Pentacene Oligomerization
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