The estimation of the signal-to-noise ratio of a nanoparticle

The quality of a single-domain nanoparticle as a signal processing device is estimated with the aid of the signal-to-noise ratio (SNR) characteristic. In the absence of an external field, the magnetic moment of a uniaxial particle flips spontaneously between two anti-parallel equilibrium positions ensuing customary superparamagnetism. On imposition of an external ac field, it, together with random noise, influences the magnetic switching and the SNR can be found in the framework of micromagnetic theory. The main material parameters essentially involved in the resulting expression are, the Neel relaxation time, siv, the precessional decay time, so, and also the magnetic viscosity coefficient, eta (m). In the paper we find these quantities by measuring the complex magnetic susceptibility as a function of frequency and polarizing field. Using these data, we estimate the SNR for the nanometre-size grains of a cobalt ferrofluid.