Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets

Abstract

We study the interplay between the effects of surface anisotropy and dipolar interactions in monodisperse assemblies of nanomagnets with oriented anisotropy. We derive asymptotic formulas for the assembly magnetization, taking into account temperature, applied field, core and surface anisotropy, and dipolar interparticle interactions. We find that the interplay between surface anisotropy and dipolar interactions is well described by the analytical expression of the assembly magnetization derived here: the overall sign of the product of the two parameters governing the surface and the dipolar contributions determines whether intrinsic and collective terms compete or have synergistic effects on the magnetization. This is illustrated by the magnetization curves of γ -Fe 2 O 3 nanoparticle assemblies in the low concentration limit.

Probing core and shell contributions to exchange bias in Co/Co<inf>3</inf>O<inf>4</inf> nanoparticles of controlled size

“…Their distinct properties are mainly connected to the finite size effects related to the reduced number of magnetic ions in the enclosed volume [4]. Additionally, surface and interface effects related to the symmetry breaking at physical boundaries of the materials cause spin disorder and frustration along with the interparticle interactions [5]. An interesting class of nanoparticles (NP) is found when ferromagnetic (FM) and antiferromagnetic (AF) materials are combined together in a core/shell structure.…”

The effects of surface spin on magnetic properties of weak magnetic ZnLa0.02Fe1.98O4 nanoparticles

“…While the sample is annealed at 1,000°C, the SSL becomes thinner or disappears, as shown in Figure 5c, and the M ( H ) loop behaves as PM with a linear loop shape in the field range used. Therefore, the gradual decrease in M max for the samples UD700, UD800, UD900, and UD1000 can be assigned to the decrease of M SSL  [32]. …”

Single-Particle Phenomena in Magnetic Nanostructures

“…[110]). In the case of an assembly of magnetic nanoparticles, this model is used to compute the ac susceptibility and to investigate the competition between (intrinsic) surface effects and dipolar interactions within an assembly of magnetic nanoparticles [111][112][113][114].…”