Magnetization of superparamagnetics in the state of mechanical anisotropy

TL;DR

This paper investigates how strong magnetic anisotropy in nanoparticles influences the magnetization behavior of magnetic fluids, especially under mechanical anisotropy, revealing significant deviations from classical models.

Contribution

It demonstrates that mechanical anisotropy alters the magnetization curve, making it deviate from Langevin behavior and approach a hyperbolic tangent shape, with notable effects on Curie law in powders.

Findings

Magnetization curve shifts between Langevin and hyperbolic tangent forms.

Increased anisotropy causes the curve to resemble a hyperbolic tangent.

Mechanical anisotropy significantly affects the Curie law in powders.

Abstract

The internal energy of magnetic anisotropy for some nanoparticles dominates over the thermal energy even at room temperature. Strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of the magnetic fluid. This influence is substantial if the system of nanoparticles is in a state of mechanical anisotropy in which the anisotropy axes of the particles have the same direction. In this work, it is shown that the magnetization curve of the magnetic fluid in a state of mechanical anisotropy is significantly different from that of Langevin. It is located between the Langevin and hyperbolic tangent curves and with increasing anisotropy takes progressively the hyperbolic tangent shape. It is also shown that in case of powder samples, the mechanical anisotropy leads to substantial quantitative changes in the Curie law.