Biquadratic exchange coupling in epitaxial Co₂MnSi/Cr/Fe trilayers

Interlayer exchange coupling (IEC) behavior in epitaxial Co₂MnSi (20 nm)/Cr/Fe (7 nm) trilayers has been investigated against Cr spacer thickness (t_Cr = 0.3-6.3 nm). High-quality trilayer samples have grown on a Cr (5 nm)/Au (30 nm)/Cr (15 nm) buffer layer on a MgO substrate by ultrahigh vacuum (UHV) compatible dc sputtering method. A simple numerical simulation model has been used to explain magnetization process, which shows good agreement with the experimental M - H curves. The values of bilinear and biquadratic coupling energy (J₁ and J₂) and the cubic anisotropy energy of Co₂MnSi and Fe (K_CMS and K _Fe) have been determined uniquely from the simulations. As a result, we have found a dominating contribution of biquadratic (90°) coupling and absence of bilinear (180°) coupling in all the samples with nonferromagnetic coupling. It has also been found that, the energetical competition between 90° coupling energy and anisotropy energy largely affects the magnetization process due to different easy directions of bottom Co₂MnSi <110> and Fe <100>.