Nanosized Core-Shell Ni/Au System and its Properties

Abstract

Core-shell Ni/Au nanoparticles are synthesized by successive reduction of aqueous solutions of nickel sulfate and chloroauric acid by sodium tetrahydroborate. Results of analysis of absorption spectra show that the position of the plasmon absorption peak (507 nm) for Au-shell (1 nm) corresponds to the one for individual gold nanoparticles of the same size. Discussion of the published results about the blocking temperature TB in the core-shell systems, synthesized by different methods, and obtained results (TB = 14 ± 0.5 K for nickel core), and HRTEM and elemental analysis results allowed to show that there is linear dependence lgТВ – lgD and ТВ – V. It is estimated the average coefficient of magnetic anisotropy K ≈ 4.5∙103 J/m3). For Ni-core with special small sizes in the ferromagnetic state there is no magnetization saturation in the field up to 20 kOe. This is the typical behavior for them in the superparamagnetic state also.