Evidence for impurity-induced frustration in La2CuO4

Zero-field muon spin rotation and magnetization measurements were performed in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by M=Mg2+ spinless impurity. It is shown that while the doping dependence of the sublattice magnetization (M(x)) is nearly the same for both compounds, the N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the Zn-doped compound. This difference, not taken into account within a simple dilution model, is associated with the frustration induced by the Zn2+ impurity onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin stiffness is derived and found to be reduced by Zn doping more significantly than expected within a dilution model. The effect of the structural modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure

Evidence for impurity-induced frustration in La2CuO4

Zero-field muon spin rotation and magnetization measurements were performed in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by M=Mg2+ spinless impurity. It is shown that while the doping dependence of the sublattice magnetization (M(x)) is nearly the same for both compounds, the N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the Zn-doped compound. This difference, not taken into account within a simple dilution model, is associated with the frustration induced by the Zn2+ impurity onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin stiffness is derived and found to be reduced by Zn doping more significantly than expected within a dilution model. The effect of the structural modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure

Mutual independence of critical temperature and superfluid density under pressure in optimally electron-doped superconducting LaFeAsO1−x_{1-x}Fx_{x}

The superconducting properties of LaFeAsO$_{1-x}$F$_{x}$ in conditions of optimal electron-doping are investigated upon the application of external pressure up to $\sim 23$ kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature $T_{c}$ and the low-temperature saturation value for the ratio $n_{s}/m^{*}$ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of $\sim 30$ % is reported for $n_{s}/m^{*}$ at the maximum pressure value while $T_{c}$ is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of non-magnetic impurities on multi-band superconductivity into account. In particular, the unique possibility to modify the ratio between intra-band and inter-bands scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model.Comment: 8 pages (Main text: 5 pages. Paper merged with supplemental information), 5 figure

Kernel chemical composition and flour quality of wheat in response to nitrogen sources and doses.

The chemical composition of wheat kernels (Triticum aestivum L.) directly affects the quality of flour by modifying its functional and technological properties, determining its use by the industry. Field trials were conducted with wheat genotypes BRS 208 and BRS Pardela to evaluate the impact of different forms of urea (conventional, with urease inhibitor, and polymer-protected) and doses of nitrogen applied in topdressing (0, 40, 80 and 120 kg ha-1) in kernel chemical composition and flour technological quality. The experimental design was randomized block with 3x4 factorial structure, with four replications. The data were submitted to analysis of variance (ANOVA) with regression for nitrogen doses, and comparison of means for genotypes and forms of urea by Tukey's test (p&#8804;0.05). Although the genotypes evaluated presented significant differences regarding kernel chemical composition and quality of flour, similar responses were observed for the variables evaluated, forms of urea, and doses of nitrogen. Application of urea with urease inhibitor increased starch content in the kernels, and polymer-protected urea reduced flour yield. A positive linear regression was observed between nitrogen doses and protein (R2=0.706) and ash (R2=0.990; p<0.01), and negative with lipid content (R2=0.836; p<0.01). However, the application of increasing doses of nitrogen reduced kernel volume density (R2=0.864; p<0.01) and brightness of flour (L*; R2=0.977; p<0.01). In addition to breeding, the application of adequate doses using various sources of mineral nitrogen could be used as an additional procedure to obtain raw materials with the desired chemical composition profile. Keywords. Grain quality, polymer-protected urea, Triticum aestivum L., urease inhibitor (NBPT) Resumo: A composição química dos grãos de trigo (Triticum aestivum L.) afeta diretamente a qualidade da farinha obtida, modificando suas propriedades funcionais e tecnológicas, determinando seu uso pela indústria. Diante disso, experimentos a campo foram conduzidos com dois genótipos de trigo (BRS 208 e BRS Pardela) para avaliar o efeito de formas de ureia (convencional, com inibidor de urease e protegida por polímero) e doses de nitrogênio em cobertura (0, 40, 80 e 120 kg ha-1) na composição química do grão e qualidade tecnológica da farinha de trigo. O delineamento experimental foi em blocos casualizados, esquema fatorial 3x4, com quatro repetições. Os dados foram submetidos a análise de variância (ANOVA), regressão (doses de nitrogênio), e comparação de médias (genótipos e formas de ureia) pelo teste de Tukey (p&#8804;0,05). Apesar dos genótipos avaliados apresentarem diferença significativas em relação a composição química do grão e qualidade da farinha, ambos apresentaram respostas similares as variáveis avaliadas, formas de ureia e doses de nitrogênio. Aplicação de ureia com inibidor de urease aumentou o teor de amido no grão, e a ureia protegida reduziu o rendimento de farinha. Observou-se regressão linear positiva entre doses de nitrogênio e teor de proteína (R2=0,706) e cinzas (R2=0,990; p<0,01), e negativa com o teor de lipídios nos grãos (R2=0,836; p<0,01). Outrossim, a aplicação de doses crescentes de nitrogênio reduziu o peso hectolitro do grão (R2=0,864; p<0,01) e luminosidade da farinha (L*; R2=0,977; p<0,01). Em adição ao melhoramento genético, a aplicação de doses adequadas utilizando diferentes fontes de nitrogênio mineral pode ser recomendado como procedimento para obtenção de matéria-prima de qualidade. -chave. Inibidor de urease (NBPT), qualidade do grão, Triticum aestivum L., ureia protegida por polímer

Doses de nitrogênio em cobertura e formas de ureia no desempenho agronômico de genótipos de trigo.

O objetivo foi avaliar o efeito de doses de adubação nitrogenada em cobertura, provenientes de diferentes formas de ureia, em genótipos de trigo em sistema de semeadura direta. Os três genótipos avaliados foram: cultivares BRS 208 e BRS Pardela e linhagem IWT 04008, em Londrina-PR, totalizando três experimentos. O delineamento experimental utilizado foi de blocos casualizados em esquema fatorial 3 x 4, com quatro repetições, avaliando-se três formas de ureia em cobertura (ureia convencional, ureia com inibidor de urease e ureia protegida) com quatro doses de nitrogênio (N) (0, 40, 80 e 120 kg ha-1) aplicadas 20 dias após a emergência. Os dados obtidos nos experimentos foram analisados conjuntamente para avaliar o efeito de genótipo. As cultivares BRS 208 e BRS Pardela são mais produtivas do que a linhagem IWT 04008. O incremento das doses de N aumenta o ciclo até o espigamento e até a maturação, a massa seca da folha bandeira, o número de espigas m-2, o teor de nitrogênio do grão a porcentagem de acamamento, porém reduz a massa de mil grãos, o rendimento e o peso do hectolitro. Com a ocorrência de chuva logo após a aplicação, as formas de ureia em cobertura não interferem nas características agronômicas do trigo