Low-temperature electrical conductivity of LaNi1-xFexO3

We report the electrical conductivity between 2 and 300 K for LaNi1-xFexO3 across the composition-controlled metal-insulator (m-i) transition. Using a method first suggested by Mobius, we identify the critical concentration x(c) to be 0.3 for the m-i transition. The negative temperature coefficient of resistivity observed at low temperatures in the metallic phase follows a temperature dependence characteristic of disorder effects. The semiconducting compositions (x greater than or equal to 0.3) do not show a simple activation energy but exhibit variable-range hopping at high temperatures confirming that the m-i transition in this system is driven by increasing disorder effects

Organically Templated Mixed-Valent Iron Sulfates Possessing Kagome and Other Types of Layered Networks

We have been interested in developing strategies for designing new open-framework architectures. One such strategy is the case of the sulfate tetrahedron and its utilization as a primary buildingunit, in place of the silicate or the phosphate tetrahedron commonly employed for the purpose

High-pressure magnetic susceptibility of the intermediate valence system EuPd2Si2

The pressure dependence (0-7 kbar) of the magnetic susceptibility is reported for the intermediate valence system EuPd2Si2 in the temperature interval 77-300K. It is found that the thermally induced valence transition becomes more gradual on application of pressure The characteristic fluctuation temperature Tf, also seems to be pressure dependent

Ce CORE level X-ray photo electron spectroscopy of CeX2Si2 (X = Fe, Co, Ni and Cu)

Ce(3d) and (4d) core level XPS spectra of CeX = Fe, Co, Ni and Cu) suggest that the mean valence of Ce was as well as 4f hybridization strength decrease systematically from Fe to Cu. This observation is in agreement with the results of Bremstrahlung Isochromat Spectroscopy (BIS), but in disagreement with LIII-edge data reported earlier

X-RAY SPECTROSCOPIC STUDY OF TMNIX INTERMETALLIC COMPOUNDS

Chemical shifts in the L<SUB>3</SUB> absorption edge of thulium in TmNi<SUB>x</SUB> (x = 1,2,3,5 and 8.5) intermetallics were measured and the effective charge on the thulium ion in these compounds was estimated. A linear relation exists between the chemical shifts and the effective charges. It is noted that the chemical shift is a function of only the number of nearest neighbours (coordination number) of thulium in these samples. The probable reasons for the origin of a kink in the L<SUB>3</SUB> absorption curve of thulium in the TmNi<SUB>x</SUB> system are discussed

Frustrated Ising chains on the triangular lattice in Sr3NiIrO6

Inelastic neutron scattering study on the spin-chain compound Sr$_3$NiIrO$_6$ reveals gapped quasi-1D magnetic excitations. The observed one-magnon band between 29.5 and 39 meV consists of magnon modes of the Ni$^{2+}$ ions. The fitting of the spin wave spectrum reveals strongly coupled Ising-like chains along the $c$-axis that are weakly coupled into a frustrated triangular lattice in the $ab$-plane. The magnetic excitations survive up to 200 K well above the magnetic ordering temperature of $T_N \sim 75$ K, also indicating a quasi-1D nature of the magnetic interactions in Sr$_3$NiIrO$_6$. Our microscopic model is in good agreement with ab initio electronic structure calculations and explains the giant spin flip field observed in bulk magnetization measurements.Comment: 10 pages, 7 figure

X-ray absorption spectroscopic study of a mixed valence system, EuPd2Si2

L3 X-ray absorption spectroscopic study of Eu firmly establishes that the compound, EuPd2Si2, is a mixed valence system. It is found that the relative intensities of the absorption peaks corresponding to divalent and trivalent europium ions in EuPd2Si2 are a strong function of temperature.© Elsevie

3d and 4d core level X-ray photoelectron spectroscopy of mixed-valence CePd3

3d and 4d core-level XPS spectra for CePd3, a mixed-valence system, have been measured. Each spectrum exhibits two sets of structures, each corresponding to one of the valence states of cerium. Thus the usefulness of XPS, which has so far not been used extensively to investigate the mixed-valence cerium systems, is pointed out

Transport and magnetic properties of Sr2FeMoxW1−xO6Sr_2FeMo_xW{1−x}O_6

We have investigated transport and magnetic properties of a series of doubleperovskite alloys in the system $Sr_2FeMo_xW_{1−x}O_6$. These compounds exhibit a metal–insulator transition as a function of doping, x. The compounds with x in the range $1.0\geq x \geq 0.3$ show metallic behaviour in the resistivity while compounds with x in the range $0.2 \geq x \geq 0$ are insulating. All compounds with $1.0 \geq x \geq 0.2$ are ferrimagnetic, while $Sr_2FeWO_6$ (x = 0) is antiferromagnetic. The magnetization (M) is shown to increase slowly with decreasing x in the range $1.0 \geq x \geq 0.3$ due to an enhanced crystallographic ordering; however,M decreases rapidly with decreasing x thereafter (x < 0.3), probably due to composition fluctuations near the critical concentration, xc. Our data suggest primarily $Fe^{3+}–(Mo, W)^{5+}$ ordering for $x \geq 0.3$, while compositions with smaller x possibly contain both $Fe^{3+}$ and $Fe^{2+}$ species inhomogeneously due to the presence of the $W^{6+}$ state. All samples with $x \geq 0.3$ show a significant amount of negative magnetoresistance, as has been observed earlier for $Sr_2FeMoO_6$ (x = 1.0)