Vortex Pinning Properties of Phosphorous-Doped $\hbox{BaFe}_{2}\hbox{As}_{2}$ Epitaxial Films: Comparison Between $(\hbox{La},\hbox{Sr})(\hbox{Al},\hbox{Ta})\hbox{O}_{3} $ and MgO Substrates

Phosphorus-doped BaFe
₂
As
₂
(BaFe
₂
As
₂
: P) epitaxial films were fabricated on (La, Sr)(Al, Ta)O
₃
single-crystal substrates, and their crystallinity, microstructure, and transport critical current density (J
_c
) properties were characterized. Compared with those of previously reported BaFe
₂
As
₂
: P epitaxial films on MgO substrates, a decrease in the self-field J
_c
and strong pinning properties along the c-axis under high magnetic fields were observed. These results can be understood by considering the poor crystallinity and the large density of the domain boundary pinning centers of the present films on (La, Sr)(Al, Ta)O
₃
, which would be caused by a thin reaction layer produced between the BaFe
₂
As
₂
: P film and the (La, Sr)(Al, Ta)O
₃
substrate.