Magnetic shape anisotropy of high-axial-ratio cobalt nanoparticles in nanogranular films

Abstract

Magnetic shape anisotropy is a principle guiding the nano-scale design of magnetic hetero-structures against competitive thermal fluctuation. Here, we have fabricated self-organized nanogranular films comprising ellipsoidal ferromagnetic nanoparticles with a wide range of aspect ratios from 0.6 to 6.1. Designed to have a significantly higher anisotropy field greater than 100 mT, these particles are not magnetically coupled with a single-domain state. Such a structure allows the coherent rotation of magnetization with respect to the particle axial ratio alone. Thanks to its shape anisotropy, the thermal stability of ferromagnetism in the ellipsoidal particle is several hundred kelvins greater than that of the sphere case. Enhanced thermal stability yields nanoscale hard magnetism seamlessly integrated with the matrix's dielectric and optical functions, paving the way for next-generation integrated nanosystems.