Ni80Fe20 permalloy nanoparticles with narrow size distribution and homogeneous composition have been prepared by the polyol processing at 180 °C for 2 h and their particle sizes can be tunable in the size range of 20∼440 nm by proper addition of K2PtCl4
agent. X-ray diffraction results show that the NiFe nanoparticles are of face centered cubic structure. The addition of K2PtCl4 does not affect the composition of NiFe NPs but decreases the particle size remarkably. Both saturation magnetization and coercivity of the
as-prepared NiFe nanoparticles decrease with decreasing particle size. Annealed at 280 °C, however, the saturation magnetization of various sized NiFe nanoparticles increases drastically and approaches to the bulk for the ∼440 nm NiFe particles, and a maximum coercivity (∼270 Oe)
happens at a critical size of ∼50 nm. The magnetic property dependency of these NiFe nanoparticles on annealing has been discussed by considering the surface chemistry.
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