10.2.1 Particles with Rectangular Shape

In order to study the influence of the shape of the nanoparticles another set with rectangular shape has been created. Each particle is a hexahedron with $165 \times 55 \times 10 \mathrm{nm}$ edge length. The particles are separated by 5 nm. The demagnetization curve for parallel and antiparallel alignment and in comparison with elliptical particles is given in Fig. 10.4.

Due to the inhomogeneous magnetization of the rectangular particles in equilibrium, the chain of rectangular particles is not as stable as that of elliptical particles. Thus, the magnetization drops already for small external fields and the switching fields are considerably lower. The switching field is 56 kA/m for antiparallel initial magnetization. The demagnetizing curve of the initially parallel magnetized particles shows a plateau at $J/J_\mathrm{s}=-0.38$, which is again caused by the stabilizing effect of the outer particles, which have switched already. Snapshots of the magnetization reversal process are given in Fig. 10.5. In contrast to the elliptical particles (cf. Fig. 10.3(a)), which reverse their magnetization almost at the same time, the rectangular particles do so consecutively. Thus, a stabilized antiparallel pattern is formed.

Figure 10.4: Demagnetization curves for a chain of elliptical and rectangular particles with parallel and antiparallel initial magnetization.

Figure 10.5: Snapshot of the magnetization reversal process of a chain of six rectangular particles.

[Initially parallel magnetization.]

[Initially antiparallel magnetization.]