Thermodynamic properties of small magnetic particles

Abstract

We investigate the equilibrium magnetic properties of a simple cubic small ferromagnetic particle under an external magnetic field. Although the particle is small, it can not be considered as a single-domain unit. The magnetic moments are represented by unitary spin vectors and we consider ferromagnetic interactions between nearest-neighbor spins. The coupling between spins is given in terms of the classical Heisenberg Hamiltonian and we also include a Zeeman contribution and a single-ion uniaxial anisotropy. The size of the particle changes from one to twelve lattice spacings. We employ in our study mean-filed calculations and Monte Carlo simulations. The magnetization and susceptibility curves as a function of temperature show that an uniaxial anisotropy can mimic a ferromagnetic or an antiferromagnetic coupling, depending on the angle between the external magnetic field and the easy axis.

Laser spectroscopy of finite size and covering effects in magnetite nanoparticles

“…This approach enables to obtain rather accurate quantitative results and is widely used in nanophysics now. In particular, a number of calculations for magnetically uniform clusters have been carried out [27][28][29][30][31]. The investigation of the surface effects in the magnetic NPs FePt was presented by Labaye et al [32]; the authors considered the effect of the surface anisotropy on an isolated single-domain spherical NP using atomic Monte Carlo simulation of the low-temperature spin ordering.…”

“…This approach enables one to obtain rather accurate quantitative results and is widely used in nanophysics now. In particular, a number of calculations for magnetically uniform clusters have been carried out [27][28][29][30][31].…”