In Situ Analysis of Phase and Magnetic Transformation Process in Fe-Pt Nanoparticles

Abstract:

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The process of phase transformation in individual Fe-Pt and Fe-Pt-Cu nanoparticles synthesized by the reverse micelle method with chemical homogeneity and mono-dispersion has been investigated by in-situ high-resolution electron microscopy (HREM) observation and in-situ nano-beam diffraction (NBD). The Fe-Pt particles, initially polycrystalline with the chemically disordered fcc (A1) phase, were reconstructed into A1 single crystals between 550 and 650°C, followed by a phase transformation from A1 to the chemically ordered fct (L10) phase between 650 and 680°C. The coalescence began almost concurrently with the phase transformation. They were transformed into round-shaped single-crystalline particles between 680 and 720°C. Similar processes were also observed in the Fe-Pt-Cu nanoparticles. The temperatures at which these processes occurred were substantially lower than those required for the Fe-Pt nanoparticles. We investigated the magnetic-field distribution of a submicron-size island comprising isolated L10 Fe-Pt nanoparticles magnetized along one direction by using in-situ electron holography at elevated temperatures. Although the magnetization decreased between 212 and 412°C to 25% of the strength at 25°C, it recovered 67% of the initial strength during cooling. However, when an island was heated to 512°C, the magnetization diminished and did not recover during cooling. The Curie temperature (Tc) was determined to be 350°C and was in good agreement with the Tc determined by bulk measurements, which was approximately 100°C lower than the Tc for bulk Fe55Pt45.

Info:

Periodical:

Materials Science Forum (Volumes 561-565)

Main Theme:

Edited by:

Young Won Chang, Nack J. Kim and Chong Soo Lee

Pages:

2111-2114

DOI:

10.4028/www.scientific.net/MSF.561-565.2111

Citation:

M. Nakanishi et al., "In Situ Analysis of Phase and Magnetic Transformation Process in Fe-Pt Nanoparticles", Materials Science Forum, Vols. 561-565, pp. 2111-2114, 2007

Online since:

October 2007

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$35.00

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