Structure, Magnetism, and Transport in SrTiO$_{3}$(001) / La$_{1-x}$Sr$_{x}$CoO$_{3}$: Evidence for Interfacial Magnetic Phase Separation

Doped cobaltites have proven to be excellent choices for the study of the magneto-electronic phase separation phenomenon. Strong motivation exists for the study of these materials in films and heterostructures, the effect of dimensional confinement on this phase separation being a prime example. We investigated the structure, magnetism, and magnetotransport, in epitaxial La$_{1-x}$Sr$_{x}$CoO$_{3}$ on SrTiO$_{3}$ (001). We have observed deterioration in ferromagnetism and conductivity in the thin film limit (e.g. $<$ 8 nm at x = 0.50). We demonstrate that this can be definitively ascribed to interfacial magnetoelectronic phase separation. Key observations are the existence of an intercluster ``GMR'', anomalous multiterminal transport, strongly non-gaussian resistance fluctuations, and direct measurement of short-range ferromagnetic order by SANS. The thickness of the phase-separated region diverges as the doping is reduced from x = 0.50 to x = 0.18, and it can also be induced by deposition of SrTiO$_{3}$ overlayers. STEM/EELS data rule out the possibility of chemical phase separation proving that the deterioration in magnetic and electronic properties near the interface with SrTiO$_{3}$ is due to an intrinsic magnetic phase separation effect. [Supported by NSF and DOE].