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Heteroepitaxial CeO₂ (800. 3em{0ex}nm) ∕L₀. ₆₇Ca₀. ₃₃MnO₃ (4000. 3em{0ex}nm) film structures have been pulsed laser deposited on LaAlO₃ (001) single crystals to fabricate two terminal resistance switching devices. Ag∕CeO₂∕L₀. ₆₇Ca₀. ₃₃MnO₃ junctions exhibit reproducible switching between a high resistance state (HRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 10^5. Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime. Successive temperature crossover of electronic transport from the thermal activation of the deep levels (E₀=3200. 3em{0ex}meV) at high temperatures to thermal activation of the shallow levels (E₀=400. 3em{0ex}meV) and finally at low temperatures to the regime of temperature independent resistance, usually associated with quantum tunneling, has been found for the insulating HRS. The temperature dependence of the LRS reveals a para-to-ferromagnetic phase transition in the L₀. ₆₇Ca₀. ₃₃MnO₃ (LCMO) electrode at T₂=2600. 3em{0ex}K and an anomaly at lower temperatures 2000. 3em{0ex}K corresponding to the Curie temperature of the Mn^4+ depleted part of the LCMO film. Current-voltage characteristics in the LRS are highly nonlinear, and show negative differential conductivity (NDC). We suggest that the reversible resistance switching ocurrs due to the electric field induced nucleation of filament-type conducting valence-shifted CeOₗ domains inside the insulating CeO₂ matrix. The abrupt insulator-to-metal transition is the result of localization of 4f electronic states in Ce^3+ ions and the subsequent appearance of hole conductivity in the oxygen p-bands. NDC at low temperatures is relied upon the interband scattering of CeOₗ carriers from a low energy, high mobility valley into a high energy valley with low mobility.
Fors et al. (Tue,) studied this question.