Phys. Rev. B 81, 184418 (2010)

M. Ziese, I. Vrejoiu and D. Hesse 

Abstract

The structural, magnetic, and magnetotransport properties of SrRuO₃ films grown on SrTiO₃ (001) substrates were investigated with the aim to determine the crystalline symmetry, crystalline orientation, and magnetocrystalline anisotropy of an ultrathin (5 nm) SrRuO₃film. 60- and 40-nm-thick SrRuO₃ films were extensively studied by transmission electron microscopy as well as magnetic and magnetotransport techniques, respectively. These studies showed orthorhombic symmetry with a slight monoclinic distortion and a well-defined long-range order of crystallographic domains with the [001]_o axis parallel to terraces on the slightly vicinal SrTiO₃substrate. The magnetocrystalline anisotropy is very strong. The easy axis lies in the (001)_o plane under a temperature-dependent angle of about 35° with respect to the [110]_o direction that is along the film normal. Below 70 K indications for a spin reorientation transition were detected. The angular-dependent anisotropic magnetoresistance shows distinctive characteristics of the monoclinic symmetry that can be used as a fingerprint. Transmission electron microscopy images of the 5 nm thin SrRuO₃ film show a coherently strained state. Using the fingerprints from the angular magnetoresistance it could be clearly shown that this ultrathin SrRuO₃ film, although grown in step flow growth as well, has still monoclinic symmetry, but lacks long-range order of the crystallographic domains. A fraction of 30–40 % of misaligned domains (rotated in plane by 90°) was estimated from the magnetoresistance curves.