L1-FePt/Fe nanocomposite thin films are promising candidates for excellent performance permanent magnets, owing to the large magnetocrystalline anisotropy of FePt (K=7×10 erg/cc [1]) and high saturation magnetization of Fe. The theoretical energy product of FePt/Fe nanocomposite thin films could be up to 90 MGOe [2]. However, the maximum energy product has been obtained in FePt/Fe nanocomposite thin films is 52.8 MGOe [3]. It is well known that a uniform and nanoscale soft magnetic phase which completely exchange-coupled with the hard magnetic phase is the key issue to get high energy product. In addition, it is widely believed that grain size, especially of soft magnetic phase, is a critical parameter for the exchange coupling effect. Therefore, considerable attentions have been focused on the design of FePt/Fe nanocomposite thin films. It has been proved that the energy product of multilayer FePt/Fe thin films is higher than that one of bilayer FePt/Fe thin films and could be further improved by optimization of microstructure and modulation periods [4-5]. In the present work, the effects of modulation periods on magnetic and structural properties of FePt/Fe multilayer thin films were investigated.
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