Effect of MgO Addition on Structural and Magnetic Properties of (001)-Textured FePt Thin Films

This paper explores (FePt)$_{100 - {\rm x}}$–(MgO)$_{\rm x}$ films with ${\rm x} = 0-6.13$, deposited on an MgO underlayer at elevated temperatures by sputtering. The films exhibit good (001) texture and perpendicular anisotropy. The effects of adding MgO are summarized as follows: 1) the (001) alignment is degraded, increasing the in-plane squareness ratio (S$_{//}$ ); 2) a linear dilution of magnetization at an applied field of 6 Tesla was observed; and 3) a critical MgO content of 1 vol. % was found for chemical ordering, microstructure, and anisotropic field $(H_{\rm k})$. Below this critical content, the ordering of FePt and its microstructure remain similar to those with ${\rm x} = 0$ but with a markedly enhanced $H_{\rm k}$. As $x$ exceeded 1 vol. %, the ordering declined linearly with increasing MgO content. Additionally, a well-defined granular structure was formed and $H_{\rm k}$ was reduced. The decrease in the lattice constant along the c-axis as $x$ increased between 0 and 1 vol. % reveals that the enhancement of $H_{\rm k}$ is related to the relaxation of the residual strain/stress that originates from the ordering transformation of FePt. Adding the proper amount of MgO improved the magnetic properties of (001)-textured FePt.