Начальная восприимчивость в системах магнитных эллипсоидальных наночастиц

In this work, we use molecular dynamics simulations to investigate the system of magnetic ellipsoidal nanoparticles with two different orientations of the dipole inside each particle. We consider dipoles directed along or perpendicular to the main axis of rotation. Such investigation allows us to determine the influence of the particles' anisotropy on the behavior and properties of the system. The initial susceptibility of the system was investigated and a cluster analysis was made. The obtained results revealed the influence of the orientation of the magnetic moment inside the particles of the same shape on the self-organization of the system, its microscopic and macroscopic properties. For the case of a parallel main orientation axis, the following was found: the initial susceptibility of particles whose shape is close to spherical increases faster and reaches higher values than in the case of ellipsoidal particles. The perpendicular orientation of the magnetic moment does not affect the initial susceptibility as significantly as in the previous case: increase in the magnetic moment leads to increase in the initial susceptibility, while the shape of the particle practically does not affect it.

Relation between Initial Magnetization Curve and Grain Size of Nanocrystalline NdFeB Magnets

The volume fraction of the single domain size particles can be directly estimated from the initial magnetization of thermally demagnetized magnets. Multi-domain grains present initial magnetization curve with high initial susceptibility, whereas single-domain grains present low susceptibility initial magnetization curve. In the case of single domain size particles, the coercivity mechanism is coherent rotation and the Stoner-Wohlfarth (SW) model can be applied. From the initial magnetization curve of magnets, the volume fraction of grains with diameter less than 0.3 micrometers can be estimated in NdFeB magnets. This is possible because the Nd2Fe14B phase is single domain below 0.3 micrometers.