Homogeneous strain-relaxation effects in La0.67Ca0.33MnO3 films grown on NdGaO3

Abstract

X-ray diffraction and transport measurements on a series of La0.67Ca0.33MnO3 films grown on (110)-cut NdGaO3 substrates are presented. Contrary to widespread belief assuming strain-free growth, this work shows the presence of strain in a 42nm film. On increasing thickness structural relaxation occurs, reaching a bulklike state for 500nm. No evidence of coexistence of strained and relaxed regions is found. The evolution of lattice parameters toward bulk values is accompanied by an increase of the metal-to-insulator transition temperature and a decrease of the polaron activation energy. Therefore, strain effects cannot always be neglected in La0.67Ca0.33MnO3 films grown on small-mismatch NdGaO3.

Fingerprint of dynamical spin-charge correlations in the tunneling spectra of colossal magnetoresistive manganites

“…The resistivity (ρ) of the films was measured in a four-point configuration, with the current flowing parallel to the film plane, along one of the main pseudocubic axis. Both kind of films exhibit a transition from insulator-to metal-like behavior at a temperature T MI lower than that of bulk compounds, as expected for films under biaxial strain [6,7,9,10,11,12].…”

“…Reciprocal space mapping for LCMO/STO films confirmed an in-plane parameter equal to that of the substrate and a strongly reduced out-of-plane lattice parameter (c ∼ 3.80 Å) [2]. The LCMO/NGO film is weakly strained (c ∼ 3.87 Å) and compressed on average in the plane [6]. As estimated from Laue oscillations, the thickness of the films is well above the dead-layer thickness [7,8].…”

“…For LCMO/STO, T MI =154 K while for LCMO/NGO, T MI =235 K. The residual resistivities are 5 mΩ cm and 0.35 mΩ cm, respectively. By taking advantage of the shift in T MI due to substrate-induced strain [6,7,9,10,11,12], we accessed the metallic and insulating phases in a wide range of temperatures.…”

Strain induced magnetic domain evolution and spin reorientation transition in epitaxial manganite films

“…The simplest explanation for these observations can be based on the spatial variation of strain in the film. While a previous report on LCMO grown on (001) NGO reveals a critical thickness of ≃ 500 nm for fully relaxed bulk like state, 14 it is possible that at intermediate thickness of ≃ 200 nm of our film both strained and relaxed regions coexist due to partial strain relaxation. Although the branching of domains is expected near the edge of the sample, all CL regions observed in the film lie well within the sample boundaries.…”

“…The simplest explanation for these observations can be based on the spatial variation of strain in the film. While a previous report on LCMO grown on (001) NGO reveals a critical thickness of ≃ 500 nm for fully relaxed bulk like state, 14 We have taken a number of scans at different places of the film and observed only ∼ 5% of such CL regions.…”