We investigated the relationship between the magnetic hysteresis loop and domain structure modulation of an artificial material, a quasi-antiferromagnet (AFM) with domains of alternating antiparallel magnetization fabricated by a strong 90° magnetic coupling between two ferromagnetic layers through an Fe-O thin layer. High-resolution Kerr images show simultaneous magnetization rotation, nucleation, and growth of stripe-type domains with maintained magnetization along the longitudinal direction of the domain. The nucleation and growth were dominant in the magnetization reversal of the quasi-AFM. By fitting not only the magnetization curve but also the domain structure to the Landau-Lifshitz-Gilbert equation, the 90° coupling coefficients were properly obtained, which enables us to design the magnetic structure of the quasi-AFM.
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