Static and dynamic properties of noncollinear magnetized ferromagnetic films

The dynamic matrix method was employed to perform theoretical calculations for investigating both static and dynamic characteristics of thick ferromagnetic films. This approach considers situations where a noncollinear equilibrium magnetization exists along the thickness due to a thickness-dependent uniaxial anisotropy and interfacial interactions in a synthetic antiferromagnet. In the former scenario, the study exposes a correlation between noncollinear static magnetization and a nonmonotonic dependence of ferromagnetic resonance frequency, where a frequency decrease is observed at low fields in the unsaturated regime. Regarding the synthetic antiferromagnet structure, the research demonstrates noncoherent magnetization rotation in the spin-flop regime, with twisted magnetization states influencing the critical and nucleation fields that define the spin-flop region. The results of the investigation were compared to the macrospin approach, where the magnetization is assumed to be uniform along the thickness. The study suggests that the contribution of noncollinear magnetic moments may mimic the role of the biquadratic interaction in the macrospin model, implying that such a biquadratic term may be overestimated in coupled ferromagnetic films with thicknesses exceeding the material's intrinsic exchange length. Finally, the model was compared with experimental data obtained from a Py/Ir/Py synthetic antiferromagnet, demonstrating that the theoretical consideration of a twisting equilibrium state of the magnetization precisely reproduces the observed dynamic and static properties of the nanostructure.