Superconductivity at 5.2 K in ZrTe3 polycrystals and the effect of Cu, Ag intercalation

We report the occurrence of superconductivity in polycrystalline samples of ZrTe3 at 5.2 K temperature at ambient pressure. The superconducting state coexists with the charge density wave (CDW) phase, which sets in at 63K. The intercalation of Cu or Ag, does not have any bearing on the superconducting transition temperature but suppresses the CDW state. The feature of CDW anomaly in these compounds is clearly seen in the DC magnetization data. Resistivity data is analysed to estimate the relative loss of carriers and reduction in the nested Fermi surface area upon CDW formation in the ZrTe3 and the intercalated compounds.Comment: 5 pages, 8 figure

Residual resistivity ratio and its relation to the positive magnetoresistance behavior in natural multilayer LaMn2Ge2; relevance to artificial multilayer physics

Results of low temperature magnetoresistance ($\Delta\rho/\rho$) and isothermal magnetization (M) measurements on polycrystalline ferromagnetic (T_C close to 300 K) natural multilayers, LaMn_{2+x}Ge_{2-y}Si_y, are reported. It is found that the samples with large residual resistivity ratio, $\rho(300K)/\rho(4.2K)$, exhibit large positive magnetoresistance at high magnetic fields. The Kohler's rule is not obeyed in these alloys. In addition, at 4.5 K, there is a tendency towards linear variation of $\Delta\rho/\rho$ with magnetic field with increasing $\rho(300K)/\rho(4.2K$); however, the field dependence of $\Delta\rho/\rho$ does not track that of M, thereby suggesting that the magnetoresistance originates from non-magnetic layers. It is interesting that these experimental findings on bulk polycrystals are qualitatively similar to what is seen in artificially grown multilayer systems recently.Comment: 5 pages, 3 figures, separate figures. This work is a follow-up of our earlier paper in APL, Ref. : APL Vol 71, pp 2385 (1997

An insight into spin-chain magnetism through Moessbauer spectroscopic investigations in Eu-doped Ca3Co2O6 and Ca3CoRhO6

We report the results of 151Eu Moessbauer effect and magnetization measurements in the Eu-doped Ca3Co2O6 and Ca3CoRhO6, which are of great current interest in the fields of spin-chain magnetism and geometrical frustration. We find that there is a pronounced increase in the line-width of the Moessbauer spectra below a certain characteristic temperature which is well-above the one at which three-diensional ordering features set in. This unusual broadening of the spectra indicates the existence of a characteristic temperature in these 'exotic' magnetic systems, attributable to the onset of incipient one-dimensional magnetic order. This is inferred from an intriguing correlation of this characteristic temperature with the paramagnetic Curie temperature (a measure of intrachain coupling strength in these cases)

Transport and magnetic anomalies due to A-site ionic size mismatch in La0.5_{0.5}Ca0.5−x_{0.5-x}Ba_{x}MnO3_3

We present results of electrical resistivity, magnetoresistance and ac and dc magnetic susceptibility on polycrystalline samples of the type La(0.5)Ca(0.5-x)Ba(x)MnO(3) synthesized under identical heat treatment conditions. The substitution of larger Ba ions for Ca results in a non- monotonic variation of the curie temperature as the system evolves from a charge ordered insulating state for x=0 to a ferromagnetic metallic state for x=0.5. An intermediate compositino, x=0.1, interestingly exhibits ferromagnetic. insulating behaviour with thermal hysteresis in ac chi around the curie tem- perature (120K). The x=0.2 and 0.3 compounds exhibit semiconducting like behavior as the temperature is lowered below 300K, with a broad peak in rho around 80-100K: These compositions exhibit a weak increase in rho as the temperature lowered below 30K, indicative of electron localization effects. These compositions also undergo ferromagnetic transitions below about 200 and 235K respectively, though these are non-hysteretic; above all, for these compositions, MR is large and conveniently measurable over the entire tempera- ture range of measurement below Tc. This experimental finding may be of interest from the application point of view. We infer that the A-site ionic-size mismatch plays a crucial role in the deciding these properties.Comment: 5 pages, 6 Figures, Resubmitted with extended abstract on 26 Nov, 199