  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.
