Effective magnetic anisotropy enhancement of FePt nanocrystals through shape control

• We investigate the magnetic anisotropy of different shaped FePt nanostructures.
• Rod shaped FePt nanostructures show the highest effective magnetic anisotropy.
• Effective magnetic anisotropy is tuned by shape control.

Magnetic properties of spherical, cubic, star and rod shaped FePt nanostructures have been investigated. Field dependence of magnetization measurements showed that approach to saturation magnetization behavior of the samples is shape dependent. When compared to spherical nanoparticles, eightfold magnetic field has to be applied to saturate nanorods. The effective magnetic anisotropies were determined by using temperature dependence of magnetization experiments and Stoner-Wohlfarth theory. The key result of the work is that engineering on the shape of the nanostructures leads to significant increase of their effective magnetic anisotropy. Cubic nanoparticles were found to have the lowest and nanorods the highest effective magnetic anisotropy constant of 1.3×105 Jm−3 and 2.7×105 Jm−3, respectively. The physical origin of this difference was ascribed to the high shape anisotropy of the rod shaped nanostructures combined with the low magnetocrysralline anisotropy of fcc FePt. By evaluating rod-shaped nanocrystals as prolate spheroids, their shape anisotropy was calculated as 1.0×105 Jm−3, which is in very good agreement with the experimental result.