1. Synthesis, structural characterization and magnetic properties of Fe/Pt coreshell nanoparticles.
- Author
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Pisane, K. L., Singh, Sobhit, and Seehra, M. S.
- Subjects
NANOPARTICLES ,MAGNETIC properties ,MAGNETIC entropy ,BIOMACROMOLECULES ,ADIABATIC demagnetization - Abstract
Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with D
o =3.0 nm and distribution width λD =0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size=3.1 nm. Measurements of magnetization M vs. T (2K-350K) in magnetic fields up to 90 kOe show a blocking temperature TB =13K below which hysteresis loops are observed with coercivity HC increasing with decreasing T reaching HC =750Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies fm =10 Hz-5 kHz is measured to determine the change in TB with fm using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency fo =5.3×1010 Hz and anisotropy constant Ka =3.6×106 ergs/ cm3 . A fit of the M vs. H data up to H=90 kOe for T>TB to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness. [ABSTRACT FROM AUTHOR]- Published
- 2015
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