Giant Enhancement of Magnetic Anisotropy in Ultrathin Manganite Films via Nanoscale 1D Periodic Depth Modulation

The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites $(\mathrm{La},\mathrm{Sr}){\mathrm{MnO}}_{3}$ has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ (LSMO) films grown on (001) ${\mathrm{SrTiO}}_{3}$ substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along $⟨110⟩$ directions, with a 50-fold enhanced anisotropy energy density of $5.6\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{erg}/{\mathrm{cm}}^{3}$ within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the $c$-axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations.