Diffuse neutron scattering study of magnetic correlations in half-dopedLa0.5Ca0.5−xSrxMnO3manganites (x=0.1, 0.3, and 0.4)

Abstract

The short-range-ordered magnetic correlations have been studied in half-doped ${\text{La}}_{0.5}{\text{Ca}}_{0.5\ensuremath{-}x}{\text{Sr}}_{x}{\text{MnO}}_{3}$ ($x=0.1$, 0.3, and 0.4) compounds by polarized neutron scattering technique. On doping ${\text{Sr}}^{2+}$ for ${\text{Ca}}^{2+}$ ion, these compounds with $x=0.1$, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and $A$-type, and $A$-type antiferromagnetic ordering, respectively. Magnetic diffuse scattering is observed in all the compounds above and below their respective magnetic ordering temperatures and is attributed to magnetic polarons. The correlations are primarily ferromagnetic in nature above ${T}_{\text{N}}$, although a small antiferromagnetic contribution is also evident. Additionally, in samples $x=0.1$ and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse reflections are observed indicating correlations between magnetic polarons. On lowering temperature below ${T}_{\text{N}}$, the diffuse scattering corresponding to ferromagnetic correlations is suppressed and the long-range-ordered antiferromagnetic state is established. However, the short-range-ordered correlations indicated by enhanced spin-flip scattering at low $Q$ coexist with long-range-ordered state down to 3 K. In $x=0.4$ sample with $A$-type antiferromagnetic ordering, superlattice diffuse reflections are absent. Additionally, in comparison to $x=0.1$ and 0.3 sample, the enhanced spin-flip scattering at low $Q$ is reduced at 310 K, and as temperature is reduced below 200 K, it becomes negligibly low. The variation in radial correlation function, $g(r)$ with temperature indicates rapid suppression of ferromagnetic correlations at the first nearest neighbor on approaching ${T}_{\text{N}}$. Sample $x=0.4$ exhibits growth of ferromagnetic phase at intermediate temperatures $(\ensuremath{\sim}200\text{ }\text{K})$. This has been further explored using small-angle neutron scattering and neutron depolarization techniques.