The effect of viscosity on the phase of the nanoparticle magnetization induced by a harmonic applied field

The temperature of magnetic nanoparticles can be estimated with excellent accuracy using the ratio of the harmonics of the magnetization induced by a harmonic magnetic field. The harmonics can be measured in vivo with high sensitivity. The method has been generalized to measure any physical property influencing the nanoparticle Brownian motion, including temperature, viscosity and bound state. We present theory and preliminary data suggesting that the phase of the harmonics can also be used to estimate the viscosity. The use of the phase should allow more sensitive measurements and alternative ways of separating dynamic from static effects.