Interpolation Formula for Magnetization of the Magnetic Nanofluid

Author: Simon Chkhaidze
Co-authors: A. Ugulava, G. Mchedlishvili, R. Abramishvili
Keywords: superparamagnetism, magnetic nanoparticles, nanomaterials
Annotation:

Magnetic nanoparticles are characterized by two vector quantities - the anisotropy axis and the magnetic moment. In the limit of low fields (at the beginning of the magnetization process), the anisotropy axes of the particles of the magnetic nanofluid are randomly directed, and in the case of strong fields they are polarized along the magnetic field (mechanical anisotropy). In the first limiting case, the system is magnetized following the Langevin curve, and in the second, by a special curve close in shape to the curve of the hyperbolic tangent. To study the transient between two limiting cases, we applied an interpolation theory that should take into account the gradual increase in the polarization of the axes of nanoparticles in the magnetization process. The main idea of this work is the representation of the magnetic nanofluid in the transient process in the form of a set of two magneto-thermodynamic subsystems with a variable number of particles (a two-component model): subsystems of nanoparticles with chaotically oriented axes and subsystems with oriented axes. In the process of magnetization, transitions from the first subsystem to the second subsystem occur, i.e. reduction of chaotic particles and an increase in oriented ones. The equilibrium condition between subsystems for intermediate values of the magnetic field is considered to be the equality of the partial potentials of the subsystems. Within the framework of this model, the interpolation formula for the magnetization of a magnetic fluid is obtained. It is shown that the magnetization curve of the interpolation theory lies between two known curves - the Langevin curve and the hyperbolic tangent curve. The Curie constant of the magnetic nanofluid, calculated on the basis of the interpolation formula, does not exceed its usual value, following from the Langevin theory.