Role of atomic vacancies and second-neighbor antiferromagnetic-exchange coupling in a ferromagnetic nanoparticle

Abstract

Several factors may be responsible for disorder and frustration in a magnetic nanoparticle, including atomic vacancies on the surface and inside, impurity atoms, long-range magnetic exchange coupling, etc. We use Monte-Carlo simulations within the Heisenberg model to examine the role of randomly distributed atomic vacancies and long-range magnetic-exchange coupling on the temperature-dependent magnetic properties of ferromagnetic nanoparticles. In particular, we study the role of the second-neighbor antiferromagnetic exchange coupling and missing atoms inside the particle resulting in broken nearby bonds. We find that both factors may enhance the superparamagnetic behaviors of such particles.

Figures (6)

• Figure 1: (a) Magnetization and (b) susceptibility as a function of temperature for different second-neighbor antiferromagnetic couplings.
• Figure 2: Variation of critical temperature $T_c$ as a function of second-neighbor antiferromagnetic exchange coupling ($J_b'$).
• Figure 3: Finite-size effect on the behavior of (a) magnetization and (b) susceptibility as a function of temperature for various edge lengths $L$.
• Figure 4: (a) Magnetization and (b) susceptibility as a function of temperature for different fractions of atomic vacancies denoted by $f$.
• Figure 5: Variation of susceptibility peak as a function concentration of atomic vacancies.