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

L1
₀
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
₀
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
₀
ordering. The order degrees of FePt, CoPt, and FePd films with and without cap layers, (S
_w/
, S
_w/o
), 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
₀
(100) crystal and possesses a high-order degree.