Magnetization State in Magnetic Nanoparticle Agglomerates

We examined magnetization states of agglomerates for two types of nanoparticle agglomerate systems, where primary crystallites have either blocked magnetization or are superparamagnetic at room temperature. We determined the magnetization state of the agglomerates with measuring magnetic permeability as a function of frequency and measuring magnetization as a function of temperature for zero-field cooled and field-cooled samples. Then we examined specifically the magnetization state of agglomerates made from blocked crystallites and we used magnetic flux measurements at different magnetic conditions. Our results show that in the case of superparamagnetic behavior of individual crystallites also the agglomerate can retain superparamagnetic behavior, whereas for crystallites with blocked magnetization nonuniform magnetization state of the agglomerate is possible.