Control of ${boldsymbol {c}}$ -Axis Orientation of ${boldsymbol {L}}textbf {1}_{mathbf{0}}$ Ordered FePt, CoPt, and FePd Alloy Thin Films Deposited on MgO(001) Substrates

摘要

L1 films formed on (001)-oriented underlayers or substrates may involve (100) crystal with the c-axis lying in the film plane in addition to (001) crystal with the c-axis normal to the film surface. In this paper, FePt, CoPt, and FePd alloy films with L1 structure are prepared on MgO(001) single-crystal substrates. The c-axis orientation is accurately controlled to be perpendicular by introducing a thin MgO cap layer on magnetic films with disordered structure prepared by low-temperature deposition at 200 °C and by annealing the bilayer films at 600 °C. The phase transformation preferentially occurs along the perpendicular direction in the MgO/(FePt, CoPt, FePd)/MgO sandwich structures. Furthermore, the cap layer promotes L1 ordering. The order degrees of FePt, CoPt, and FePd films with and without cap layers, (S, S), are (0.82, 0.58), (0.36, 0.30), and (0.72, 0.62), respectively. The FePt film with cap layer shows a strong perpendicular magnetic anisotropy and a very low in-plane coercivity because of which the film does not include L1(100) crystal and possesses a high-order degree.