Reviving dead layer magnetism by interface tailoring with strong spin-orbit materials

Ferromagnetic (FM) onset in doped manganates is usually accompanied by a metal-insulator transition and colossal magneto-resistance. In the extremely thin film limit, materials tend to lose their functionality and become non-magnetic and insulating, i.e. “dead”. We have discovered that below the dead-layer thickness, through interfacial coupling, a strong re-entrant FM-insulating phase with very large magneto-resistance can appear. We created heterostructures of La_.7Ca_.3MnO₃ (LCMO)-X-LCMO on SrTiO₃ (001) where X is the buffer layer (SrTiO₃, CaRuO₃ and SrRuO₃). The buffer materials were selected based on their structure, electronic properties and magnetism to identify how the interfacial coupling might affect the magnetic and electronic properties in LCMO. We found that SrRuO₃, an FM-metal with strong spin-orbit coupling, has the most drastic effect on the magnetic onset temperature (~200K T_C increase) and net magnetization, even with the addition of only a single unit cell of SrRuO₃. We also find these films to remain insulating despite this magnetic resuscitation, pointing toward a novel magnetic order beyond the usual double-exchange. We will discuss the underlying physics using atomic-scale microscopy and spectroscopy.