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Li, Jing

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Tailoring magnetic properties of core/shell nanoparticles

2004-08-02 , Zeng, Hao , Sun, Shouheng , Li, Jing , Liu, J. Ping , Wang, Z. L. (Zhong Lin)

Bimagnetic FePt/MFe₂O₄ sM=Fe,Cod core/shell nanoparticles are synthesized via high-temperature solution phase coating of 3.5 nm FePt core with MFe₂O₄ shell. The thickness of the shell is controlled from 0.5 to 3 nm. An assembly of the core/shell nanoparticles shows a smooth magnetization transition under an external field, indicating effective exchange coupling between the FePt core and the oxide shell. The coercivity of the FePt/Fe₃O₄ particles depends on the volume ratio of the hard and soft phases, consistent with previous theoretical predictions. These bimagnetic core/shell nanoparticles represent a class of nanostructured magnetic materials with their properties tunable by varying the chemical composition and thickness of the coating materials.

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Interface structures in FePt/Fe₃Pt hard-soft exchange-coupled magnetic nanocomposites

2003-05-26 , Li, Jing , Wang, Z. L. (Zhong Lin) , Zeng, Hao , Sun, Shouheng , Liu, J. Ping

Self-assembly of FePt and Fe₃O₄ nanoparticles of different sizes led to various FePt–Fe₃O₄ nanocomposites. Annealing the composite under reducing atmosphere at 650 and 700 °C induced magnetically hard FePt phase and magnetically soft Fe₃Pt phase. The FePt and Fe₃Pt phases were either linked by a common interface or coexisted within one grain as domains with sizes <10 nm. This ensures the effective exchange coupling of magnetically hard and soft phases. High-resolution transmission electron microscopy studies provide detailed structural characterization for the FePt based nanocomposites.

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Interparticle interactions in annealed FePt nanoparticle assemblies

2002-09 , Zeng, Hao , Li, Jing , Wang, Z. L. (Zhong Lin) , Liu, J. Ping , Sun, Shouheng

Thermal treatment of self-assembled FePt nanoparticles reduces the interparticle distances, resulting in dramatic changes in the type and strength of interparticle interactions. Consequently, magnetic properties such as the hysteresis and magnetization reversal mechanisms are strongly affected. It is suggested that controlled annealing of self-assembled nanoparticles may offer a novel approach for producing hard magnetic nanocomposites.