Dependence of Nucleation Field on the Size of Soft Phase in Magnetic Hard–Soft Exchange Coupling Nanocomposites

Abstract

Hard–soft exchange coupling nanocomposites have critical applications in various important materials. The magnetic properties of nanocomposite permanent magnetic films improve with a higher nucleation field (Hns) of the soft magnetic phase. Hns is sensitive to the thickness (ds) of the soft magnetic layer. Understanding the dependence of Hns and irreversible field (Hirr) on ds, especially at the nanometric scale, is crucial for comprehending the magnetic mechanism and facilitating the design and preparation of high-performance nanocomposite permanent magnets. However, during the high-temperature deposition process, diffusion between hard and soft magnetic phases occurs, leading to the generation of other phases. This makes it challenging to accurately reflect the relationship between Hns and ds. To address this issue, we successfully fabricated high-quality SmCo5/Fe nanocomposite bilayer films with different soft magnetic thicknesses and high textures by controlling the preparation process. We conducted a quantitative analysis of the relationship between Hns and ds within the range of 2–40 nm. Based on the experimental results, we propose a new theoretical simulation formula that enhances the understanding of the characteristics at the interface between the soft magnetic and hard magnetic phases. The theoretical simulation results show that a thin softened hard layer of about 4–6 nm thickness exists at the interfacial region, which concurrently reverses with the soft magnetic phase during the demagnetization process. Our results offer the generality and critical basis for the further study of hard–soft nanocomposite magnetic materials.