Thickness-dependent physical properties of La_1/3Sr_2/3FeO₃ thin films grown on SrTiO₃ (001) and (111) substrates

We have investigated the thickness-dependent transport properties of La_1/3Sr_2/3FeO₃ thin films grown on SrTiO₃ (001) and (111) substrates. At a thickness of ∼40 nm, both films show a clear transition in resistivity associated with the characteristic charge disproportionation at approximately 190 K. The transition temperature of the charge disproportionation is nearly unchanged with decreasing film thickness down to a certain thickness of ∼13 nm for both orientations, while the change in resistivity gradually decreases. Below this thickness, the transition becomes unclear, strongly suggesting the suppression of the charge disproportionation at the critical thickness of ∼13 nm. Furthermore, there is no significant difference in the thickness dependence of La_1/3Sr_2/3FeO₃ thin films between the (001) and (111) orientations. The negligible crystallographic-orientation dependence may reflect the isotropic nature for the domain of charge disproportionation states in La_1/3Sr_2/3FeO₃.