Magnetic force fields of isolated small nanoparticle clusters (original) (raw)
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A detailed numerical simulation of quasistatic hysteresis loops of dense clusters of interacting magnetic nanoparticles is carried out. Both clusters of magnetically soft and magnetically hard nanoparticles are considered. The clusters are characterized by an average particle diameter D, the cluster radius R c , the particle saturation magne-tization M s , and the uniaxial anisotropy constant K. The number of particles in the cluster varies between N p = 30-120. The particle centers are randomly distributed within the cluster, their easy anisotropy axes being randomly oriented. It is shown that a dilute assembly of identical random clusters of magnetic nanoparticles can be characterized by two dimensionless parameters: 1) the relative strength of magneto-dipole interaction, K/M s 2 , and the average particle concentration within the cluster, η = VN p /V c. Here V is the nanoparticle volume, and V c is the volume of the cluster, respectively. In the strong interaction limit, M s η/H a >> 1, where H a = 2K/M s is the anisotropy field, the ultimate hysteresis loops of dilute assemblies of
Equilibrium and dynamic behaviour of (weakly) interacting assemblies of magnetic nanoparticles
Journal of Physics: Conference Series, 2014
A still open issue related with the study of assemblies of magnetic nanoparticles, deposited on a substrate or embedded in a matrix, is that of the interplay between intrinsic features of the nanoparticles pertaining to their finite-size and boundary effects, and the collective effects entailed by their mutual interactions and their interactions with the hosting matrix or substrate. In this work we develop a semi-analytical approach that allows us to derive expressions for the magnetization and the susceptibility of interacting assemblies of single-domain ferromagnetic nanoparticles. We find that upon tuning the physical parameters pertaining to each nanoparticle or the shape of the assembly and its spatial arrangement, surface and inter-particle interactions may be set up to play additive or comptetive roles leading to assemblies with optimal magnetic properties.