Tuning the ground state of La0.67Ca0.33MnO3films via coherent gr

Abstract

The commensurate La 0.67 Ca 0.33 MnO 3 films, of which the bulk is a ferromagnetic-metal (FM), can show strikingly different ground states when grown on NdGaO 3 substrates of various orientations. With a larger orthorhombic lattice distortion in the substrates, the (110) films can grow essentially strain-free, but the (100) and (001) films are anisotropically strained, accompanied by an increased orthorhombicity. As a result, while the (110) films show constantly a bulklike FM ground state, the others behave dramatically different, i.e., they show a tunable antiferromagnetic-insulator (AFI) phase below ∼250 K with strong phase instability in the wide temperature range and at low magnetic fields. Considering that in La 1−x Ca x MnO 3 system the AFI phase is highly involved with the orthorhombic lattice distortion, the different ground state in (100) and (001) films could be ascribed to the epitaxial anisotropic strain, which enhances the orthorhombicity of the films via increasing the rotation and deformation of the MnO 6 octahedra.

Annealing assisted substrate coherency and high-temperature antiferromagnetic insulating transition in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

“…In fact, by comparing the magnetotransport properties of LCMO films grown on the NGO substrates with various orientations, we have excluded the interfacial chemical diffusion and variation of La:Ca doping ratio during ex-situ annealing, and demonstrated that the AFI phase is elastic-driven. 33,35 In Fig. 1(c), the ω-2θ linear scans of the 10-h annealed films (20 and 40 nm) show sharp Laue fringes, further confirming that the LCMO films have high crystal quality and sharp interface with the underlying substrates.…”

“…34,35 With decreasing the thickness to 20 nm, the annealed film shows a higher ρ below T AFI , indicating an enhanced AFI phase. In fact, by comparing the magnetotransport properties of LCMO films grown on the NGO substrates with various orientations, we have excluded the interfacial chemical diffusion and variation of La:Ca doping ratio during ex-situ annealing, and demonstrated that the AFI phase is elastic-driven.…”

“…28 On the other hand, the reflections from the as-grown and annealed films are both sharp and concentrated, and have exactly the same in-plane lattice spaces as those of the substrates, suggesting that LCMO/NGO(001) films are coherently strained even after being ex-situ annealed. 17,26,29,35 That means the strain relaxation during annealing may not be the driven force for the AFI phase.…”

“…More strikingly, though the bulk LCMO is optimally doped in the ferromagnetic-metal (FM) ground state, the LCMO/NGO(001) films, after being annealed in oxygen atmosphere, show an antiferromagnetic insulator phase transition at ∼250 K and the PS with the coexistence of antiferromagnetic-insulating (AFI) and FM phases at the temperature below. [32][33][34][35] In the early work we have demonstrated that the ex-situ annealing process and the NGO(001) substrate stabilized in-plane anisotropic strain state are both indispensable for the formation of AFI phase. 34,35 However, the detailed evolutions of the strain state and octahedral behavior during annealing, which are central for understanding the AFI phase and PS, are still unclear.…”

“…[32][33][34][35] In the early work we have demonstrated that the ex-situ annealing process and the NGO(001) substrate stabilized in-plane anisotropic strain state are both indispensable for the formation of AFI phase. 34,35 However, the detailed evolutions of the strain state and octahedral behavior during annealing, which are central for understanding the AFI phase and PS, are still unclear. Here we develop a new strategy by investigating the surface morphology and magnetotransport property in parallel from the LCMO/NGO(001) films with various thicknesses after being ex-situ annealed under various annealing parameters.…”