Perpendicular magnetic anisotropy in La1−xSrxCoO2.5+δ/La2/3Sr1/3MnO3/La1−xSrxCoO2.5+δ trilayers (x=0.05–0.5)

Perpendicular magnetic anisotropy (PMA) of magnetic materials has received much attention because of its potential application to spintronics devices. In general, the tensely strained $(001)\text{\ensuremath{-}}\mathrm{L}{\mathrm{a}}_2/3\mathrm{S}{\mathrm{r}}_1/3\mathrm{Mn}{\mathrm{O}}₃$ (LSMO) layer is easy plane. Here we demonstrate that the tensile LSMO layer will exhibit an out-of-plane magnetic anisotropy if it is sandwiched between two $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_x\mathrm{Co}{\mathrm{O}}_{2.5+\ensuremath{\delta}}$ (LSCO) layers. The most remarkable observation is that the PMA enhances with the increase of the Sr content in LSCO. It is $\ensuremath{\sim}2.7\ifmmode\times\else\texttimes\fi{}{10}⁶\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}³$ for $x=0.05$ and $\ensuremath{\sim}4.3\ifmmode\times\else\texttimes\fi{}{10}⁶\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}³$ for $x=0.5$. This value is two orders of magnitude greater than that obtained by compressively straining the LSMO film $(\ensuremath{\sim}{10}⁴\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}³)$. Analysis of high resolution lattice image shows the formation of perovskite/brownmillerite-type interfaces in the multilayers: Brownmillerite-like lattice structure forms in the interfacial layers of LSCO, resulting in a coherent tilting of adjacent $\mathrm{Mn}{\mathrm{O}}₆$ octahedra. This in turn leads to, as evidenced by the analysis of x-ray linear dichroism, selective orbital occupation thus spin reorientation. There is evidence that the brownmillerite-structured LSCO is more easily formed when $x$ is high, which explains the growth of anisotropy constant with the increase of Sr content.