Compositional Dependence of Exchange Anisotropy in Pt$_x$Mn$_{100-}$$_x$/Co$_y$Fe$_{100-}$$_y$ Films

Bilayer films consisting of a 15 nm thick Pt
_x
Mn
_100-x
(x = 48 or 15) layer and a 2 nm thick Co
_y
Fe
_100-y
(0 ≤ y ≤ 90) layer were fabricated by ultrahigh-vacuum magnetron sputtering. The Pt
₄₈
Mn
₅₂
and Pt
₁₅
Mn
₈₅
films consisted of face-centered tetragonal (FCT) and face-centered cubic (FCC) structures, respectively. The effect of composition of CoFe films on the unidirectional anisotropy constant (Jk) in the Pt
_x
Mn
_100-x
/Co
_y
Fe
_100-
y
bilayer films and the optimum conditions for producing large Jk were determined. The FCT and FCC PtMn films annealed at 370 °C for 6 h both exhibited maximum J
_k
when the film composition was Co
₇₀
Fe
₃₀
. Blocking temperatures of the FCT and FCC PtMn films were 410 °C and 160 °C, respectively. All the bilayer films possess flat surfaces. These results indicate that the obtained Pt-Mn films-with low roughness, high exchange bias, and high blocking temperature-will be practical candidates as the antiferromagnetic layer in spintronic devices.