Estimation of electronic and structural influence on the thermal magnetic properties of clusters

Effect of coverage on the magnetic properties of -COOH, -SH, and -NH2 ligand-protected cobalt nanoparticles

Implementation of magnetic nanoparticles in biomedicine requires their passivation, which often comes at a cost of diminished magnetic properties. For the design of nano-agents with targeted magnetic behaviour, it is important to distinguish between ligands which can improve desired performance, and those that reduce it. Carboxylic acid-, thiol-, and amine-protected cobalt nanoparticles were studied by density functional theory calculations to model the impact of ligand coverage on the magnetic properties. The simulations show that the functional group, arrangement, and coverage density of the ligand coating control both the total magnetic moment and magnetic anisotropy energy of the nanoparticle, as well as the distribution of local spin magnetic moments across the metallic core. Captured effects of ligand binding on the orbital moments of cobalt atoms were insignificant. Out of the three ligand families, only carboxylic acid coatings increased the magnetic moments of cobalt nanoparticles, while amines and thiols quenched them. Calculated anisotropy energies of protected nanoparticles consistently increased with the growing ligand density, reaching the highest values for a 100% coverage of both carboxylic acid and thiol coatings. However, the binding nature of the two functional groups showed opposite impacts on the d-states of interacting cobalt atoms. This study has thus established important principles for the design of biocompatible magnetic nanocomposites, highlighting different routes to achieve desired magnetic behaviour.

Magnetism of PrAl₂ nanoparticle investigated with a quantum simulation model

For many years, micromagnetism and Monte Carlo simulation have served as the two main tools for studying the magnetic structures and physical properties of nanomagnets. However, the two approaches are based on classical physics, and thus lack the flexibility to deal with complex nanosystems, such as those of very tiny size or consisting of ions of different elements. To overcome the difficulty, a quantum simulation model has been proposed and a new computational algorithm developed in the present work. Both have been successfully applied to an assumed PrAl₂ nanoparticle to study its magnetic behavior in external magnetic fields exerted along the crystal axes. The theoretical results obtained with the model and the new algorithm are reasonable physically and exhibit strong finite-size effects. The model can be generalized to study the magnetic configurations and physical properties of more complicated nanosystems, such as nanowires, nanotubes, etc.

Magnetic enhancement in nanoscale CoRh particles

The influence of size reduction on the magnetism of CoRh has been studied on a system of isolated nanometric spherical bimetallic ultrafine particles embedded in a polymer matrix. Pulsed fields up to 30 T were used in order to approach the magnetic saturation ( M(S)). Particles with a mean diameter of 1.65 (+/-0.1) nm display a value of 2.38 micro(B) per CoRh unit strongly enhanced compared to values calculated or measured on a bulk alloy. These results were interpreted as the first evidence of the cooperative role of both alloying and size reduction to the enhancement of M(S) in this system associating a 3d FM metal with a 4d metal.