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

This paper explores (FePt)_{100 - x}-(MgO)_x films with 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 _k). Below this critical content, the ordering of FePt and its microstructure remain similar to those with x = 0 but with a markedly enhanced H _k. As x exceeded 1 vol. %, the ordering declined linearly with increasing MgO content. Additionally, a well-defined granular structure was formed and H _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 _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.