Fabrication, characterization, and magnetic and electronic properties of epitaxial La$_{0.5}$Sr$_{0.5}$CoO$_{3}$ films

Bulk La$_{1-x}$Sr$_{x}$CoO$_{3}$ (LSCO) has received considerable attention with regard to magnetic phase separation. Fabrication of epitaxial films would provide a means to study this phase separation under dimensional confinement. We have investigated the properties of epitaxial films of x = 0.5 LSCO on SrTiO$_{3}$ (001) by reactive d.c. sputtering from compound targets. Structure and properties were studied as a function of sputtering pressure, O$_{2}$/Ar ratio, and post-deposition O$_{2}$ treatment. Optimized conditions result in single phase, stoichiometric, substantially relaxed, epitaxial films. At a fixed O$_{2}$ / Ar ratio, two distinct regimes of total sputtering pressure ($P)$ occur. Films grown at $P>$ 50 mTorr have properties close to bulk; they are ferromagnetic ($T_{C} \quad \approx $ 230 K, $M_{S} \quad \approx $ 2 $\mu _{B}$ / Co), have a metallic-like $\rho (T)$ at all $T$, and exhibit 10 {\%} magnetoresistance at $T_{C}$. For $P \quad <$ 50 mTorr, we obtain lower surface roughness and narrower rocking curves but with low moment, insulating $\rho (T)$, and increased out-of-plane lattice parameter due to O deficiency. Similarly, a dramatic enhancement in physical properties, and elimination of a CoO minority phase, is obtained when cooling in 500 Torr of O$_{2}$. The results demonstrate good control over the oxygen stoichiometry, and therefore physical properties. Work supported by NSF DMR.