Magnetic response of thermally blocked magnetic nanoparticles in a pulsed magnetic field

In order to detect fast changes of the Brownian relaxation time due to reaction kinetics on the surface of magnetic particles or particle-clustering processes, we have developed a method that uses pulsed magnetic fields and detects the relaxation of the magnetic response on the time scale of milliseconds. We compared measurements in the frequency domain with the time domain measurement using particle suspensions with three different median sizes. The results obtained with the two methods agreed well. Time domain determination of Brownian relaxation was then used to study the reaction kinetics of the clustering process when sodium chloride solution was added to a magnetic nanoparticle suspension.