Electronic and Magnetic Structure of ${\rm L}1_{0}$-FePt Nanoparticle Embedded in FePt Random Alloy

Nanocomposite permanent magnets made of hard and soft magnetic nanoparticles are important nanostructured materials. They, however, present substantial theoretical challenges due to the need to treat the electronic interactions quantum-mechanically whilst dealing with a large number of atoms. In this presentation, we show a direct quantum mechanical simulation of magnetic nano-structures made of spherical L1
₀
-FePt nanoparticles, with diameter within 2.5-5 nm, embedded in an fct-FePt random alloy. The calculation is performed using the locally self-consistent multiple scattering (LSMS) method, a linear scaling ab initio method capable of treating tens of thousands of atoms. We found that there exists a screening region below the surface of each nanoparticle. This screening region essentially screens out the effect of the external random alloy to keep the physical properties of the interior region unchanged from the bulk of L1
₀
-FePt. Interestingly, the depth of this screening region is around 4 Aring and is independent of the size of the nanoparticles we have investigated. We will discuss the formation of this screening region and the effect of the external random alloy on the electronic and magnetic structure of the nanoparticles