Transport Properties Of Epitaxial La0 Research Articles

Thickness-dependent magnetic and electrical transport properties of epitaxial La0.7Sr0.3CoO3 films

The thickness-dependent magnetic and electrical transport properties of nearly strain-free La0.7Sr0.3CoO3 (LSCO) films grown on (001)-oriented (LaAlO3)0.3 (Sr2AlTaO6)0.7 substrates were systematically studied. A crossover from ferromagnetic/metallic to non-magnetic/insulating behavior occurs at a critical thickness (∼8 nm) that is significantly smaller than LSCO films under larger strains in reported literature. X-ray absorption measurements revealed that the difference of functional properties at reduced film thicknesses was accompanied by changes in the valence state of Co ions at the film/substrate interface.

Electrical transport in epitaxial La0.7Ca0.3MnO3 thin films

We investigated the electrical transport properties of epitaxial La0.7Ca0.3MnO3 thin films grown by metal organic deposition process on LaAlO3 single crystalline substrates. To explain the coexistence of ferromagnetic (FM)-metallic and paramagnetic (PM) -insulator phases in the same specimen, the temperature dependence of resistivity was simulated by the phenomenological percolation model which is based on the phase segregation of FM-metallic to PM-insulator. The temperature dependence of resistivity (ρ(T)) curves can be well fitted by ρ(T)=ρFMf+ρPM(1−f) with ρFM is the resistivity of the FM phase below the Curie temperature (TC), ρPM is the resistivity of the PM phase above TC and “f” is the FM volume fraction. The obtained fitting parameters have been correlated to the change in the strain in the films having various thicknesses. The ferromagnetic volume fraction (f(T)) and the reduced magnetization m(T) show monotonic and “similar” behaviors.

Influence of compressive strain on oxygen distribution in La0.7Ba0.3MnO3 thin films

The effects of annealing ambient on the structural and transport properties of epitaxial La0.7Ba0.3MnO3 films suffering large compressive strain on LaAlO3 substrates (LBMO/LAO) have been investigated. Independent of oxygen or argon ambient, a high temperature (900 °C) post-annealing process leads to a c-axis contraction, which can be attributed to the oxygen transfer from the in-plane to the out-of-plane direction. Meanwhile, the transport properties are similar with each other for both the Ar-annealed and O2-annealed films. The comparison of the ambient annealing effects between the highly strained LBMO/LAO films and negligibly strained LBMO films on SrTiO3 substrates indicates that a large in-plane compressive strain favors decreasing oxygen deficiency in the films, especially in the ab-plane.

Effect of angular-distortion-induced strain on structural and transport properties of epitaxial La0.7Sr0.3MnO3 thin films

The effect of lattice-mismatch and especially the angle-mismatch induced strain on structural and transport properties of epitaxial La0.7Sr0.3MnO3(LSMO) thin films with thicknesses of 5–70 nm has been studied by x-ray diffraction and resistivity measurements. X-ray reciprocal space maps show that the growth of LSMO films on SrTiO3(0 0 1) and (LaAlO3)0.3(Sr2AlTaO6)0.7(0 0 1) substrates induces biaxial tensile and compressive strain in the in-plane of the films, respectively. As the film thickness, t, is changed, there exist two distinct thickness ranges where different thickness dependence of transport properties was observed, irrespective of the strain type. For t < 12 nm, the metal–insulator transition temperature TP is extremely sensitive to the biaxial strain and thickness, and for t ⩾ 12 nm, TP is weakly dependent on the film thickness. We explain this variation of thickness dependence by considering the angular-distortion- induced strain and relaxation of the equilibrium rhombohedral LSMO structure.