Nonlinear dynamic thermometry: Temperature measurement using immobilized magnetic nanoparticles

Abstract

We present a new method for measuring the temperature of magnetic nanoparticles that can also be adapted to immobilized particles. The Néel relaxation mechanism, which dominates the dynamic magnetization process of immobilized magnetic nanoparticles, can be used as an intermediate parameter in a sensing model to obtain temperature information. In this paper, we use the nonlinear response properties of magnetic nanoparticles to derive an analytical expression for the relationship between the phase of cubic susceptibility and temperature. We also consider dipole–dipole interactions and the dependence on field amplitude. Under experimental conditions at selected frequencies and field amplitudes, we compare temperature measurements of magnetic nanoparticles obtained with the proposed thermometry model with those obtained from existing nonlinear dielectric relaxation models. The results show that the temperature measurements obtained from the proposed model are closer to the reference temperatures in the temperature range of 308–353 K, with a standard deviation of less than 0.1 K in the temperature measurement. This new method successfully applies the nonlinear properties of magnetic nanoparticles to high-precision dynamic temperature measurements. It extends the applicability range of temperature measurement methods to conditions with strong interactions or large ac field amplitudes. This new method is expected to be applicable in anti-magnetic environments, for example, in biochemical temperature measurements of magnetically labeled cells in vivo.