Colossal magnetoresistance of Nd2/3Sr1/3MnO3 ultrathin films grown on charge-ordered Nd1/2Ca1/2MnO3 manganite

We present a study of the interfacial interaction between a ferromagnetic metallic manganite in proximity to a charge-ordered manganite in a bilayer structure. Different thicknesses (2-45 nm) of ferromagnetic metallic Nd2/3Sr1/3MnO3 (NSMO-1/3) were grown by pulsed laser ablation on charge-ordered Nd1/2Ca1/2MnO3 (NCMO-1/2) with a fixed thickness of 175 nm on SrTiO3 (001) substrates. Electrical transport and magnetization measurements in large magnetic fields show that the metal-insulator transition temperature decreases with the NSMO-1/3 thickness down to a critical value of 4-5 nm below which NSMO-1/3 remains insulating at low temperature. The critical thickness corresponds also to the largest magnetoresistance response with the conducting phase recovered easily under the application of a magnetic field as low as 1.5 T. The insulating phase observed for the ultrathin NSMO-1/3 film is attributed to the compressive strain and the magnetic interaction in the vicinity of the charge-ordered NCMO-1/2. Magnetic measurements also show that a significant portion of the NCMO-1/2 layer magnetizes at lower field. This is a clear example of a forced phase percolation by proximity effect.