In-plane uniaxial magnetic anisotropy induced by anisotropic strain relaxation in high lattice-mismatched Dy/Sc superlattices

Abstract

We report on the magnetic and structural characterization of high lattice-mismatched [Dy${}_{2nm}$/Sc${}_{{t}_{\text{Sc}}}$] superlattices, with variable Sc thickness ${t}_{\text{Sc}}$= 2--6 nm. We find that the characteristic in-plane effective hexagonal magnetic anisotropy K${}_{6}^{6,ef}$ reverses sign and undergoes a dramatic reduction, attaining values of $\ensuremath{\approx}$13--24 kJm${}^{\ensuremath{-}3}$, when compared to K${}_{6}^{6}=\ensuremath{-}0.76$ MJm${}^{\ensuremath{-}3}$ in bulk Dy. As a result, the basal plane magnetic anisotropy is dominated by a uniaxial magnetic anisotropy (UMA) unfound in bulk Dy, which amounts to $\ensuremath{\approx}$175--142 kJm${}^{\ensuremath{-}3}$. We attribute the large downsizing in K${}_{6}^{6,ef}$ to the compression epitaxial strain, which generates a competing sixfold magnetoelastic (MEL) contribution to the magnetocrystalline (strain-free) magnetic anisotropy. Our study proves that the in-plane UMA is caused by the coupling between a giant symmetry-breaking MEL constant M${}_{\ensuremath{\gamma},2}^{2}\ensuremath{\approx}1$ GPa and a morphic orthorhombiclike strain ${\ensuremath{\varepsilon}}_{\ensuremath{\gamma},1}\ensuremath{\approx}{10}^{\ensuremath{-}4}$, whose origin resides on the arising of an in-plane anisotropic strain relaxation process of the pseudoepitaxial registry between the nonmagnetic bottom layers in the superstructure. This investigation shows a broader perspective on the crucial role played by epitaxial strains at engineering the magnetic anisotropy in multilayers.