Sakharov , V.K., R.A. Booth and S.A. Majetich, “High-frequency permeability of Ni and Co particle assemblies”, Journal of Applied Physics, Vol. 115(17), pp. 17A517, 2014. DOI: 10.1063/1.4866234
A coaxial transmission line was constructed, characterized, and calibrated for the frequency dependent measurement of complex relative permeability (μr ) and complex permittivity (εr ). The permeability of Ni powder with a grain size of < 1 μm was measured as a function of packing density to verify the system performance. 8–10 nm diameter Co nanoparticles were synthesized, dried to a powder, and measured. The real part of the permeability for the Co nanoparticles decreased over time as a result of oxidation, and decreased the overall magnetic volume due to the formation of an antiferromagnetic CoO shell. Similarly, the imaginary part of the permeability decreased as a function of oxidation. This was attributed to the insulating CoO shell reducing eddy current losses in the nanoparticle composite.
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