Dependence of exchange coupling interaction on micromagnetic constants in hard/soft magnetic bilayer systems

To elucidate the dependence of exchange coupling behavior of hard/soft magnetic bilayer systems on various micromagnetic constants, the coupling length (λ) and the nucleation field (HN) were systematically measured on five thin-film libraries made of soft magnetic/hard magnetic bilayers. Hysteresis loops of CoPt Fex Co1-x (0≤x≤1), CoPt Ni, CoPt Fe, Sm2 Co7 (Fe,Co, or Ni), and Sm2 Co7 Ni were measured using a magneto-optical Kerr effect setup. The one-dimensional model proposed by Leineweber and Kronmüller [J. Magn. Magn. Mater. 176, 145 (1997)] and micromagnetic simulations were used to interpret the behavior of λ and HN obtained by the high-throughput investigation. We found that the dominant factors determining λ and HN are the hard layer magnetic constants and the saturation magnetization (M) of the soft layer. HN and λ display a direct correlation with the domain-wall width of the hard layer and have an anticorrelation with M of the soft layers. They were found to not be substantially dependent on exchange stiffness (A) and anisotropy (K) constants within the group of soft layer materials studied here.