Interlayer coupling-driven magnetic ordering and magnetization processes in ultrathin Au/Co/Mo/Co/Au film

Interlayer magnetic coupling in an Au/Co/Mo/Co/Au system fabricated by molecular beam epitaxy was studied as a function of the thicknesses of the cobalt and molybdenum spacer layers (denoted as d_Co and d_Mo, respectively). Magnetization processes and magnetic domain structures were investigated using magneto-optical techniques. In the investigated thickness ranges, various magnetization configurations of the Co layers were observed: (A) both perpendicular, (B) perpendicular and in-plane, and (C) both in-plane. The interlayer exchange coupling field H_IEC was determined as a function of d_Mo. With increasing d_Mo, this coupling changed from antiferromagnetic with a huge coupling field of ≈0.27 T to ferromagnetic and again to antiferromagnetic. A coupling oscillation period of around 1.4 nm was deduced by comparing the experimental data with the Ruderman–Kittel–Kasuya–Yosida model. For configurations (B) and (C), oscillations of the saturation magnetic field H_SAT(d_Mo) perpendicular to the sample plane were found. Simplified and precise analytical expressions for H_SAT were proposed by considering H_IEC as well as the uniaxial magnetic anisotropy of one and both magnetic layers, respectively. Magnetic ordering was numerically modeled taking into account the dependences of layer anisotropy and exchange coupling on d_Co and d_Mo, respectively. This modeling well described the remanent magnetization map (d_Co, d_Mo) determined using the polar Kerr effect. It is also shown that H_IEC(d_Mo) induced magnetization reorientation from in-plane to out-of-plane or from out-of-plane to in-plane magnetization configurations and canted magnetization of the Co layers.