title: Exchange-coupled fct-FePd/α-Fe nanocomposite magnets converted from Pd/Fe3O4 core/shell nanoparticles.
abstract: We report the controlled synthesis of exchange-coupled face-centered tetragonal (fct) FePd/α-Fe nanocomposite magnets with variable Fe concentration. The composite was converted from Pd/Fe3O4 core/shell nanoparticles through a high-temperature annealing process in a reducing atmosphere. The shell thickness of core/shell Pd/Fe3O4 nanoparticles could be readily tuned, and subsequently the concentration of Fe in nanocomposite magnets was controlled. Upon annealing reduction, the hard magnetic fct-FePd phase was formed by the interdiffusion between reduced α-Fe and face-centered cubic (fcc) Pd, whereas the excessive α-Fe remained around the fct-FePd grains, realizing exchange coupling between the soft magnetic α-Fe and hard magnetic fct-FePd phases. Magnetic measurements showed variation in the magnetic properties of the nanocomposite magnets with different compositions, indicating distinct exchange coupling at the interfaces. The coercivity of the exchange-coupled nanocomposites could be tuned from 0.7 to 2.8 kOe and the saturation magnetization could be controlled from 93 to 160 emu g(-1). This work provides a bottom-up approach using exchange-coupled nanocomposites for engineering advanced permanent magnets with controllable magnetic properties.
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871 (P.R. China), Fax: (+86) 010-62753115.
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.forename: Yunhe
authors.initials: Y
authors.lastname: Dong
authors.forename: Wenlong
authors.initials: W
authors.lastname: Yang
authors.forename: Jing
authors.initials: J
authors.lastname: Yu
authors.forename: Zhichuan
authors.initials: Z
authors.lastname: Xu
authors.forename: Yanglong
authors.initials: Y
authors.lastname: Hou
keywords: exchange interactions; intermetallic phases; magnetic properties; nanostructures; reduction