Thermodynamic properties of magneto-anisotropic nanoparticles

The purpose of this paper is to study the thermodynamic equilibrium properties of a collection of non-interacting three-dimensional (3D) magnetically anisotropic nanoparticles in the light of classical statistical physics. Pertaining to the angular dependence (alpha) of the magnetic field with the anisotropy axis, energy landscape plots are obtained which reveal a continuous transition from a double well to a single well for alpha = pi/2 and show an asymmetric bistable shape for other values of alpha. The present analysis is related to the interpretation of equilibrium magnetization and static susceptibility of a nanomagnetic system as a function of external magnetic field, B, and temperature, T. The magnetization and susceptibility confirm the non-Langevin behaviour of magneto-anisotropic monodomain particles. The susceptibility analysis establishes the ferromagnetic-, antiferromagnetic- and paramagnetic-like coupling for various alpha. This study reveals the essential role of magneto-anisotropic energy in the interpretation of the magnetic behaviour of a collection of non-interacting single-domain nanoparticles.