Near-neighbour impurity effect on the spin-state transitions in LaCoO<SUB>3</SUB> at low temperature (12&lt;T&lt;300 K)

The low-temperature magnetic susceptibility behaviour of LaCoO3 prepared under different conditions as well as substituted samples such as LaCo0.95M0.05O3 (M=Al, Ga, Cr, Fe, Mn, Ni) and La0.98Sr0.02CoO3 have been investigated in the temperature range 12-300 K. Earlier interpretations of the magnetic susceptibility have been reexamined. In the case of LaCoO3 samples containing Al, Ga, Cr and Fe impurities spin-state transitions involving a temperature independent activation energy (~0.01 eV) are observed atT&lt;200 K. Analysis of the data indicates that either the excited state has an intermediate-spin (t52g e 1g) configuration or only half the Co ions are involved in the activated transition to the high-spin (t42g e2g ) configuration. Al3+, and Cr3+ increases the activation energy considerably. Substitution of L &#8800; 0 ions such as Mn3+ and Ni3+ or Co4+ (low-spin) seems to introduce ferromagnetic interactions and stabilizes the paramagnetic state. LaCoO3, when Co is substituted by Mn (5%) or La is substituted by Sr (2%) show giant magnetic moments. When Co is substituted by Ni (5%) a ferromagnetic ground state is observed

Magnetic susceptibility studies of lead oxyhalide glasses containing transition metal oxides

Magnetic susceptibility studies of lead oxyhalide glasses containing high concentrations of transition metal oxides such as MnO and Fe2O3 have been performed. While they exhibit predominantly antiferromagnetic interactions, the low temperature (&lt;100K) region is dominated by paramagnetic contributions. The behaviour in these glasses is found to be similar to that of covalent oxide glasses and is different from that of purely ionic sulphate glasses

Magnetoresistance of metallic perovskite oxide LaNiO3−δ_{3-\delta}

We report a study of the magnetoresistance (MR) of the metallic perovskite oxide LaNiO$_{3-\delta}$ as a function of the oxygen stoichiometry $\delta$ ($\delta \leq$ 0.14), magnetic field (H $\leq 6T$) and temperature (1.5K $\leq$ T $\leq$ 25K). We find a strong dependence of the nature of MR on the oxygen stoichiometry. The MR at low temperatures change from positive to negative as the sample becomes more oxygen deficient (i.e, $\delta$ increases). Some of the samples which are more resistive, show a resistivity minima at $T_{min}$ $\approx$ 20K. We find that in these samples the MR is positive at T > $T_{min}$ and negative for T < $T_{min}$. We conclude that in the absence of strong magnetic interaction, the negative MR in these oxides can arise from weak localisation effects.Comment: 10 pages in REVTeX format, 4 eps fig

Role of carboxylate ion and metal oxidation state on the morphology and magnetic properties of nanostructured metal carboxylates and their decomposition products

Sub-micron rods and spheres of cobalt succinate sesquihydrate and iron succinate trihydrate/pentahydrate respectively have been synthesized by the reverse micellar route. These precursors are an excellent source for the synthesis of metal and metal oxide nanoparticles. Cubes of (edge length ~ 150 nm) Fe3O4 and elongated particles of Fe2O3 (~ diameter of 200 nm) were obtained. The role of oxidation state of the metal ion in controlling the morphology of the nanostructured dicarboxylates has been investigated. Rods with shorter length were obtained when longer chain dicarboxylate was used as ligand. Heating in nitrogen atmosphere also provided pure Co and α-Fe nanoparticles. The Fe nanoparticles show nearly 100% superparamagnetism. Temperature-dependent magnetic studies show a Morin-like transition for Fe2O3 nanoparticles at 223 K and the Verwey transition at 115 K for Fe3O4 nanoparticles. Co3O4 nanoparticles showed antiferromagnetic ordering at 20 K

(Bi,Pb)<SUB>2</SUB>(Sr,Ln)<SUB>2</SUB>CuO<SUB>6</SUB> (Ln = La,Pr,Nd): new superconducting cuprates related to Bi<SUB>2</SUB>Sr<SUB>2</SUB>CuO<SUB>6+y</SUB>

A new series of BiPb-cuprates of the formula BiPbSrLnCuO6 (Ln = La, Pr, Nd), which are isotypic with the superconducting Bi-cuprate, Bi2Sr2CuO6+y, has been prepared. The new BiPb-cuprates are nonsuperconducting, but when doped with holes by replacing part of Ln with Sr, superconducting cuprates of the formula BiPbSr1+xLn1-xCuO6 showing a maximum Tc of 25K for Ln = La at x = 0.25 are obtained. Unlike the Bi-cuprates, the parent and the superconducting BiPb-cuprates are free from the structural modulation

Spin-state Equilibrium in Lanthanum Cobaltate: Effect of Magnetic & Non-magnetic Near-neighbour Impurities

1037-104

Slicing the perovskite structure into layers: synthesis of novel three-dimensional and layered perovskite oxides, ALaSrNb<SUB>2</SUB>M<SUP>II</SUP>O<SUB>9</SUB> (A= Na, Cs)

This article does not have an abstract

Magnetic interactions in the oxide systems LaNi<SUB>1&#8722;x</SUB>M<SUB>x</SUB>O<SUB>3</SUB> (M=Cr, Fe, or Co)

Magnetic susceptibilities of several members of the series of oxides of the general formula LaNi<SUB>1&#8722;x</SUB>M<SUB>x</SUB>O<SUB>3</SUB> (M=Cr, Fe, or Co) are reported. The oxides show evidence for interesting ferrimagnetic (Cr and Co) and antiferromagnetic (Fe) interactions

Doping dependence of transport and magnetic properties in La<SUB>1−x</SUB>Ca<SUB>x</SUB>VO<SUB>3</SUB>

We report temperature dependences of transport and magnetic properties of La<SUB>1&#8722;x</SUB>Ca<SUB>x</SUB>VO<SUB>3</SUB> controlled by charge carrier doping (x = 0.0 - 0.5). The system exhibits an insulator-to-metal transition concomitant with an antiferromagnetic-to-paramagnetic transition near x=0.2 with increasing substitution. Disorder effects are found to influence the low-temperature transport properties of both insulating and metallic compositions near the critical concentration. At higher temperature resistivity of the metallic compositions has a T<SUP>2</SUP> dependence close to the critical concentration (x=0.2 and 0.3) and thus provides an example of disordered Fermi liquid behaviour near the Mott transition. In contrast, at larger doping (x=0.4 and 0.5) the resistivity exhibits a T<SUP>1.5</SUP> dependence. The molar susceptibility for the metallic samples indicates substantial enhancements due to electron correlation