Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites

We report on the magnetic, resistive, and structural studies of perovskite La$_{1/3}$Sr$_{2/3}$CoO$_{3-\delta}$. By using the relation of synthesis temperature and oxygen partial pressure to oxygen stoichiometry obtained from thermogravimetric analysis, we have synthesized a series of samples with precisely controlled $\delta=0.00-0.49$. These samples show three structural phases at $\delta=0.00-0.15$, $\approx0.25$, $\approx0.5$, and two-phase behavior for other oxygen contents. The stoichiometric material with $\delta=0.00$ is a cubic ferromagnetic metal with the Curie temperature $T_{\rm C}=274$ K. The increase of $\delta$ to 0.15 is followed by a linear decrease of $T_{\rm C}$ to $\approx$ 160 K and a metal-insulator transition near the boundary of the cubic structure range. Further increase of $\delta$ results in formation of a tetragonal $2a_p\times 2a_p \times 4a_p$ phase for $\delta\approx 0.25$ and a brownmillerite phase for $\delta\approx0.5$. At low temperatures, these are weak ferromagnetic insulators (canted antiferromagnets) with magnetic transitions at $T_{\rm m}\approx230$ and 120 K, respectively. At higher temperatures, the $2a_p\times 2a_p \times 4a_p$ phase is $G$-type antiferromagnetic between 230 K and $\approx$360 K. Low temperature magnetic properties of this system for $\delta<1/3$ can be described in terms of a mixture of Co$^{3+}$ ions in the low-spin state and Co$^{4+}$ ions in the intermediate-spin state and a possible spin transition of Co$^{3+}$ to the intermediate-spin state above $T_{\rm C}$. For $\delta>1/3$, there appears to be a combination of Co$^{2+}$ and Co$^{3+}$ ions, both in the high-spin state with dominating antiferromagnetic interactions.Comment: RevTeX, 9 pages, 7 figures, to be published in Physical Review

Assessment of Ratooning Ability and Heterotic Effects for Yield and Yield Contributing Traits in Intraspecific Hybrids of Upland Cotton

The development of high yielding cotton hybrids is essential to meet the current cotton demands. On the other hand, the cotton ratooning allows to obtain maximum seed yields with early maturity of plant. Therefore, the present study was aimed to investigate the per se performance, ratooning ability and heterosis effects for yield and yield contributing traits in 28 novel hybrids through line x tester analysis by considering four varieties as lines and seven varieties as testers. Significant variability was observed for all investigated traits excluding the number of monopodial branches and boll weight traits in parents and their 28 hybrids. Among the parents, TSH 0499 and TSH 04/115 exhibited a fair performance for yield and yield contributing traits and SURABHI, TSH 0250 and VS 9-S11-1 expressed superior ratooning ability. Therefore, these parents have a potential to be exploited for the development of the efficient cotton hybrids. Among the tested F1 hybrids, TSH 0499 x TCH 1777, BGDS 1063 x TCH 1819, TSH 0499 x TCH 1819 and TSH 04/115 x SVPR 4 hybrids recorded superior performance for number of bolls, boll weight, lint index and seed cotton yield in first crop, respectively. The hybrids ARBC 19 x TSH 0250, TSH 0499 x SURABHI , TSH 0499 x TSH 0250 and TSH 0499 x TCH 1705-101 displayed good ratooning performance for number of bolls, boll weight, lint index and seed cotton yield, respectively. All the hybrids expressed a range of significantly positive and negative heterosis for tested traits. However, the observed negative heterosis for seed index is desirable since the hybrids produce more lint. The results of this study would give insights into the understanding of genetic variance present in the intra-hirsutum hybrids

Influence of Pressure on Magnetic Properties of La1−x\text{}_{1-x} Srx\text{}_{x}CoO3−δ\text{}_{3-δ}(x=0.5, 0.67, 1)

Influence of pressure on the phase transition temperature T$\text{}_{C}$ and on the spontaneous magnetisation M$\text{}_{0}$ of highly Sr substituted and oxygen nonstoichiometric La$\text{}_{1-x}$Sr$\text{}_{x}$CoO$\text{}_{3-δ}$ samples was investigated. An increase in T$\text{}_{C}$ and M$\text{}_{0}$ with pressure in investigated samples was found, indicating strengthening of ferromagnetic double exchange interactions, and the expansion of volume of ferromagnetic phase as a~result of enhancement in ferromagnetic interactions in both cluster-glass and long range ferromagnetic states. We did not observe clear correlation between changes in pressure coefficient dT$\text{}_{C}$/dP and changes in the formal oxidation state of the Co ion

Influence of Hydrostatic Pressure on Magnetic Properties of (Sr,La)(Ru,Cr,Mn)O3\text{}_{3}

An influence of hydrostatic pressure, P, on phase transition temperature, T$\text{}_{C}$, and spontaneous magnetisation, M$\text{}_{0}$, of selected perovskite ruthenates (SrRuO$\text{}_{3}$, La$\text{}_{0.2}$Sr$\text{}_{0.8}$RuO$\text{}_{3}$, SrRu$\text{}_{0.9}$Mn$\text{}_{0.1}$O$\text{}_{3}$, and SrRu$\text{}_{0.9}$Cr$\text{}_{0.1}$O$\text{}_{3}$) was determined to 12 kbar. A decrease in T$\text{}_{C}$ with pressure was found for all of the studied samples. The M$\text{}_{0}$(P) remains unchanged for most of the samples, except for the La$\text{}_{0.2}$Sr$\text{}_{0.8}$RuO$\text{}_{3}$ sample. The weakening of ferromagnetic interactions with increasing pressure is consistent with complex band structure effects related to the modulation of the Ru-O hybridisation by the change of structural distortion