Thickness-dependent properties of (110)-oriented La_1.2Sr_1.8Mn₂O₇ thin films

We have grown (110)-oriented thin films of the bilayer manganite La_1.2Sr_1.8Mn₂O₇ [n=2 phase of the Ruddlesden-Popper (RP) family] by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of these films depend strongly on the growth conditions as well as the film thickness. Optimal growth conditions of 900 °C and 100 mTorr O₂ balance the oxygenation of the n=2 phase without causing its decomposition into the n=1 and ∞ phases of the RP family. With increasing film thickness, the film evolves from a mixture of the n=1, 2, and ∞ phases to a film composed primarily of the n=2 phase. The thicker films possess bulklike properties with a ferromagnetic/paramagnetic transition that coincides with a resistivity maximum at a reduced T_c∼90 K (vs 120 K in bulk) and an anisotropy ratio, ρ_c/ρ_ab∼20–200 over the temperature range 5–380 K.