10. Elliptical Permalloy Nanoparticles

Magnetic nanoparticles have seen growing interest in recent years due to advances in fabrication, observation [134], and computational techniques [135]. Since the typical size of these particles approach the magnetic domain wall width (nm to $\mu$m range) new effects appear and can be exploited for applications. Transport phenomena and magnetoresistance effects in particular are intensively studied. In experiments different magnetic domain configurations and domain walls have been found to influence MR effects [136,137].

In this work magnetic nanoparticles of permalloy (Ni$_{80}$Fe$_{20}$) have been investigated. Micromagnetic simulations based on the Gilbert equation of motion of the magnetization have been carried out to study the magnetic reversal processes and domain configurations in single particles, arrays of isolated particles and connected (exchange coupled) particles with contact faces of different size.

The magnetic domain wall width in permalloy is approximately as large as the long axis of the particles, but effects of the magnetostatic stray field and small contact faces can stabilize certain domain configurations. The remaining domain walls can be used to investigate MR effects.