Fractal pore distribution and magnetic microstructure of pulse-electrodeposited nanocrystalline Ni and Co

Abstract

The crystalline and magnetic microstructures of nanocrystalline Ni and Co samples, with volume-averaged grain sizes between 10 and 60 nm, obtained by pulsed electrodeposition have been studied by means of small angle neutron scattering (SANS), small angle x-ray scattering (SAXS), and magnetization measurements. According to density measurements the porosity of the samples amounts to values between 0.5 and 3 %. SAXS and nuclear SANS contributions are dominated by pore scattering and reveal that the pores are distributed according to a fractal correlation function. The magnetic SANS contributions measured at zero field indicate that both n-Ni and n-Co have magnetic domains with sizes exceeding 150 nm, i.e., the domains must confine several crystallite grains. The present results of the domain sizes in n-Ni are similar to earlier literature data. For the case of n-Co the present results differ considerably from literature data, where only single-grain domains were found in n-Co samples synthesized by other methods. We attribute the difference in domain sizes in n-Co to the preparation method which in the present case yields samples of relatively high density. The field dependence of the SANS signal observed in n-Ni and n-Co shows that large domains are saturated at smaller fields than the smaller domains. The field dependence of the SANS signal is compared with the field dependence of the magnetization.