Thickness-Dependent Magnetism in Epitaxial SrFeO3-δ Thin Films

Strained oxygen-deficient perovskite SrFeO
_3-δ
(SFO) films have been epitaxially grown by pulsed laser deposition (PLD) on SrTiO
₃
(STO) (001) substrates. Oxygen deficiency of the films in comparison with the stoichiometric perovskite SrFeO
₃
is manifested in the increased lattice parameter, c = 3.97 Å, the decreased mass density, p = 4.825 gcm
^-3
, and the presence of Fe
³⁺
cations. The SFO perovskite structure is monoclinically distorted with an increase of the film thickness, resulting in the reduction of the total magnetic moment. A wasp-waisted hysteresis loop and a negative exchange bias are observed for the 69 nm thick film due to the possible magnetic sublayers arising from a proper monoclinically distorted surface layer and a substrate-locked core layer.