Synthesis and magnetic properties of silica-coated FePt nanocrystals

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Colloidal FePt nanocrystals, 6 nm in diameter, were synthesized and then coated with silica (SiO(2)) shells. The silica shell thickness could be varied from 10 to 25 nm. As-made FePt@SiO(2) nanocrystals have low magnetocrystalline anisotropy due to a compositionally disordered FePt core. When films of FePt@SiO(2) particles are annealed under hydrogen at 650 degrees C or above, the FePt core transforms to the compositionally ordered L1(0) phase, and superparamagnetic blocking temperatures exceeding room temperature are obtained. The SiO(2) shell prevents FePt coalescence at annealing temperatures up to similar to 850 degrees C. Annealing under air or nitrogen does not induce the FePt phase transition. The silica shell limits magnetic dipole coupling between the FePt nanocrystals; however, low temperature (5 K) and room temperature magnetization scans show slightly constricted hysteresis loops with coercivities that decrease systematically with decreased shell thickness, possibly resulting from differences in magnetic dipole coupling between particles.
Publisher
AMER CHEMICAL SOC
Issue Date
2006-06
Language
English
Article Type
Article
Keywords

IN-OIL MICROEMULSION; NANOSIZE SILICA; IRON-OXIDE; NANOPARTICLES; COERCIVITY; NANOCOMPOSITES; FILMS

Citation

JOURNAL OF PHYSICAL CHEMISTRY B, v.110, no.23, pp.11160 - 11166

ISSN
1520-6106
DOI
10.1021/jp060974z
URI
http://hdl.handle.net/10203/90521
Appears in Collection
CBE-Journal Papers(저널논문)
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