Interpolation theory of magnetic nanofluids magnetization

Author: Archil Ugulava
Co-authors: S. Chkhaidze, G. Mchedlishvili
Keywords: ferromagnetism, superparamagnetism, nanoparticles
Annotation:

The internal energy of the magnetic anisotropy of some nanoparticles predominates over the thermal energy even at room temperature. It is known that the magnetic anisotropy axis of the magnetic nanofluids of nanoparticles, which in the absence of a magnetic field are oriented at random, at a sufficiently strong magnetic field, are polarized along the magnetic field and the so-called mechanical anisotropy state originates. In this paper, it is shown that the magnetization curve of the subsystem of polarized particles in the case when the anisotropy energy exceeds thermal energy has a special shape similar to the shape of a hyperbolic tangent. In the present model of a magnetic nanofluid it consists of two components (subsystems) with a variable number of particles: a subsystem of particles with randomly directed axes and subsystem of particles with polarized axes. The change of the magnetic field value causes the change of the number of particles in the subsystems followed by the change the magnetization of the whole magnetic nanofluids. For a given value of the magnetic field interpolation formula of magnetic nanofluids magnetization is found from the condition that the chemical potentials of subsystems are equal. It is shown that the magnetization curve obtained on the basis of a two-component model of magnetic nanofluids, is located between the Langevin curve and the hyperbolic tangent and with increasing anisotropy takes progressively the hyperbolic tangent shape. It is also shown that in strong magnetic anisotropy saturated state of magnetization of nanoparticles occurs much earlier than it follows from the Langevin theory. This significantly increases the Curie constant.