The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO, this spin-polarized two-dimensional t2g electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the t2g nature of the carriers. First principles calculations strongly suggest that Zeeman splitting, caused by proximity magnetism and oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two-dimensional t2g electron gas.

No abstract

A non-destructive reversible resistive switching is demonstrated in single crystals of Cr-doped Mott insulator Ca2RuO4. An applied electrical bias was shown to reduce the DC resistance of the crystal by as much as 75%. The original resistance of the sample could be restored by applying an electrical bias of opposite polarity. We have studied this resistive switching as a function of the bias strength, applied magnetic field, and temperature. A combination of 2-, 3-, and 4-probe measurements provide a means to distinguish between bulk and interfacial contributions to the switching and suggests that the switching is mostly an interfacial effect. The switching was tentatively attributed to electric-field driven lattice distortions which accompany the impurity-induced Mott transition. This field effect was confirmed by temperature-dependent resistivity measurements which show that the activation energy of this material can be tuned by an applied DC electrical bias. The observed resistance switching can potentially be used for building non-volatile memory devices like resistive random access memory.

We study the resistive switching in tunnel junctions with single-crystal La2NiO4 electrodes. Such electro-resistive devices are promising candidates for future nonvolatile memory and reconfigurable logic applications thanks to their simple structure, excellent scalability and endurance. Our tunnel junctions were prepared by painting a spot of conductive silver epoxy on the surface of a La2NiO4 single crystal. The interface between the silver and the semiconducting crystal served as a natural barrier forming planar normal metal/insulator/semiconductor (N–I–S) tunnel junctions with resistances ranging from a few Ohms to more than hundred thousands of Ohms. The current–voltage (I–V) measurements performed on such junctions at room temperature demonstrated a bias-driven switching between high and low resistance states with ratios close to 100% and high endurance. A combination of 2- and 3- probe I–V measurements unambiguously demonstrated that the resistive switching is associated with the interfaces between the La2NiO4 crystal and the silver-contact electrodes, with negligible contribution from the bulk of the crystal. Similar resistive-switching phenomena in other oxide materials were previously associated with crystal-lattice distortions produced by an applied voltage/electric field. Here, we use an ultra-sensitive capacitive displacement meter to monitor the field-induced lattice distortions in situ. We observe that the crystal contraction/expansion is strongly correlated with the resistive switching. We also note that the Joule heating from dc bias may contribute to the crystal size changes. Our results provide a new insight into the origin of lattice distortions/resistive switching in transition metal oxides while the observed interfacial nature of the switching phenomenon is promising for fabrication of thin-film planar devices to be used in nonvolatile memory and logic.

No abstract