Magnetic and structural properties of magnetic colloids with a well-developed system of magnetized aggregates

The dynamical magnetic properties of a system of nanoparticle aggregates possessing an intrinsic resulting magnetic moment are studied for the first time. It is established that the processes of magnetization relaxation in magnetic colloids with a well-developed system of magnetized aggregates are similar to the processes of relaxation of magnetically ordered systems with short-range order, i.e. elastic dipole glasses. With decreasing temperature of a sample below the solidification point, the system transforms into dipole glass. The aggregates can acquire additional magnetization in the external field, which leads to the novel peculiarities of the structure formation in such a system. The results of microstructure investigation of a layer of magnetized aggregates exposed to an in-plane rotating magnetic field as well as to combined rotating and constant magnetic field acting perpendicularly to the layer are presented. Being exposed to a rotating magnetic field, the initially individual aggregates agglomerate into dusters, the rotation frequency of which depends as on the rotating field frequency as on the intensity of the additionally imposed constant magnetic field. The process of structural ordering in a layer of magnetized aggregates has been numerically simulated. (C) 2020 Elsevier B.V. All rights reserved.