Enhancement of the Magnetic Anisotropy in Rare-Earth-Free Multilayer Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2

Using the first principles method, we investigated the interface effect on the electronic structure and the magnetic properties of multilayer Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2. The thicknesses of Ag (100) and Au (100) were fixed to three monolayers, and the lattice mismatch was about 1%. The magnetic moment of Fe atoms at the interface was suppressed due to hybridization with non-magnetic Ag and Au atoms. Due to this reduction in the magnetic moments and also because of the non-magnetic volume of the Ag and Au layer, an overall 40% suppression of the magnetization was found in both systems. The hybridization between interface Ag (Au) and Fe atoms and the spin-orbit coupling associated with Ag (Au) atoms mainly contributed to the enhancement of the magnetocrystalline anisotropy. The magnetocrystalline anisotropy constant was enhanced from 0.57 MJ/m3 in pure Fe16N2 to 1.58 MJ/m3 and 0.89 MJ/m3 in Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2 multilayer systems, respectively. This enhancement in magnetocrystalline anisotropy results in an enhancement of the coercive field. The coercive fields were about 30 and 16.7 kOe in the Ag and the Au multilayer systems, respectively. Overall, we found substantial enhancements in the magnetocrystalline anisotropy constant and the coercive field due to the interface effect. This finding may suggest that the Fe16N2/Ag/Fe16N2 and the Fe16N2/Au/Fe16N2 structures can be utilized for potential rare-earth-free permanent magnets.