The review is devoted to the analysis of physical processes occurring at different stages of production and application of nanocrystalline soft magnetic materials based on Fe–Si–B doped with various chemical elements. The temperature dependences of the kinematic viscosity showed that above a critical temperature, the viscosity of multicomponent melts at the cooling stage does not coincide with the viscosity at the heating stage. Above the critical temperature, the structure of the melt is more homogeneous, the amorphous precursor from such a melt has greater plasticity and enthalpy of crystallization and, after nanocrystallization, the material has a higher permeability. The most effective inhibitor elements are insoluble in α-Fe and form a smoothed peak of heat release during crystallization. On the other hand, the finest nanograins and the highest permeability are achieved at a narrow high-temperature peak of heat release. The cluster magnetic structure of a nanocrystalline material is the cause of magnetic inhomogeneity, which affects the shape of the magnetic hysteresis loop and core losses.

The work investigated the temperature dependences of the kinematic viscosity for multicomponent melts of nanocrystalline soft magnetic alloys. It is shown that there is a linear relationship between the reduced activation energy of viscous flow E_a·(RT)⁻¹ and the pre-exponential factor ν₀. This ratio is universal for all quantities, the temperature dependence of which is expressed by the Arrhenius equation. It is shown that the activation energy of a viscous flow is linearly related to the cluster size on a natural logarithmic scale, and the melt viscosity increases with decreasing cluster size. The change in the Arrhenius plot in the anomalous zone on the temperature dependence of viscosity can be interpreted as a liquid–liquid structure transition, which begins with the disintegration of clusters and ends with the formation of a new cluster structure.

The influences of the atomic size and mass on the kinematic viscosity and self-diffusion coefficient of metal liquids have been studied. The analysis was performed with experimental data on the kinetic properties of metals at the melting temperature. Regression analysis shows that the kinematic viscosity and self-diffusion coefficient increase with an increase in the size of atoms and a decrease in their mass. Note that the atomic mass is more closely related to the kinetic properties of a metal liquid in comparison with the atomic size. It is proposed to use the size–mass factor (which is equal to the ratio of the size of an atom to a square root of its mass) to analyze the kinetic properties of a liquid. The relationship between the kinetic properties and the size–mass factor is characterized by a adjusted determination coefficient, the value of which is above 0.90. It is shown that the kinematic viscosity of a liquid and the self-diffusion coefficient decrease with an increase in the cluster size. It was determined from the dimensionless kinetic parameters that the dimensionless excess entropy at the melting temperature is close to the calculated values for the solidification point of a simple liquid.

The temperature dependences of the kinematic viscosity during heating and cooling have been investigated in Co-B melts with a boron content of up to 30.8 at. A liquid–liquid structural transition was found, which is accompanied by an increase in the activation energy and cluster size, as well as a significant decrease in the density of the melt. The liquid–liquid structural transition was associated with the formation of clusters with a short-range order of Co₂₃B₆ in the intermediate temperature region. At low and high temperatures, clusters of the order of an atomic size are active participants in the viscous flow. It was shown that with an increase in the cluster size, the activation energy increases and the viscosity of melts decreases. The formation of large Co₂₃B₆ clusters during the cooling of melt with low boron content leads to undercooling and the appearance of the transition temperature region with high activation energy, although this region does not exist during the heating stage.