Magnetization of nanomagnet assemblies: Effects of anisotropy and dipolar interactions

Abstract

We investigate the effect of anisotropy and weak dipolar interactions on the magnetization of an assembly of nanoparticles with distributed magnetic moments, i.e., assembly of magnetic nanoparticles in the one-spin approximation, with textured or random anisotropy. The magnetization of a free particle is obtained either by a numerical calculation of the partition function or analytically in the low and high field regimes, using perturbation theory and the steepest-descent approximation, respectively. The magnetization of an interacting assembly is computed analytically in the range of low and high field, and numerically using the Monte Carlo technique. Approximate analytical expressions for the assembly magnetization are provided which take account of the dipolar interactions, temperature, magnetic field, and anisotropy. The effect of anisotropy and dipolar interactions are discussed and the deviations from the Langevin law they entail are investigated, and illustrated for realistic assemblies with the lognormal moment distribution.

arXiv comment21 pages, 5 eps figures

References in corpus (11)

• Surface contribution to the anisotropy of magnetic nanoparticles
• Surface effects in nanoparticles: application to maghemite $\gamma$-Fe_{2}O_{3}
• Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles
• Hysteretic properties of a magnetic particle with strong surface anisotropy
• Classical and quantum magnetization reversal studied in nanometer-sized particles and clusters
• Field dependence of the temperature at the peak of the ZFC magnetization
• Thermodynamic perturbation theory for dipolar superparamagnets
• Boundary and finite-size effects in small magnetic systems
• Linear and nonlinear superparamagnetic relaxation at high anisotropy barriers
• Fragility of the spin-glass-like collective state to a magnetic field in an interacting Fe-C nanoparticle system
• Spin-wave theory for finite classical magnets and superparamagnetic relation

Cited by in corpus (8)

• Magnetic relaxation of a system of superparamagnetic particles weakly coupled by dipole-dipole interactions
• Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets
• Effects of dipolar interactions on the zero-field-cooled magnetization of a nanoparticle assembly
• Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles
• Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies
• Effect of dipolar interactions and DC magnetic field on the specific absorption rate of an array of magnetic nanoparticles
• The benefits of a Bayesian analysis for the characterization of magnetic nanoparticles
• Single-particle versus collective effects in assemblies of nanomagnets: screening