Thickness-dependent properties of (110)-oriented La_(1.2)Sr_(1.8)Mn_2O_7 thin films

摘要

We have grown (110)-oriented thin films of the bilayer manganite La_(1.2)Sr_(1.8)Mn_2O_7 [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 ℃ and 100 mTorr O_2 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.