Effects of oxygen incorporation in tensile ${\mathrm{La}}_{0.84}{\mathrm{Sr}}_{0.16}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ thin films during ex situ annealing

Structural changes in epitaxial ${\mathrm{La}}_{0.84}{\mathrm{Sr}}_{0.16}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ (LSMO) $\left(001\right)∕\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3\left(001\right)$ thin films are studied using x-ray scattering during thermal annealing. As oxygen atoms are incorporated during annealing ex situ in air, the unit-cell volume contracts, which is attributed to the increased ratio of ${\mathrm{Mn}}^{4+}$ ions as indicated by enhanced saturation magnetization and ferromagnetic transition temperature. The unit-cell contraction occurs rather abruptly, suggesting that a structural phase transition happens during annealing. A $200\text{−}\mathrm{\AA }$-thick film remains almost fully strained even after annealing. In this case, a fourfold structural modulation is observed which accommodates the augmented lattice strain energy.

Figure 1

Scattering profile of the as-grown LSMO (001) along the surface normal direction in (a) $200\text{−}\mathrm{\AA }$-thick film and (d) $700\text{−}\mathrm{\AA }$-thick film. Scattering profile of the as-grown LSMO (100) in the film in-plane direction in (b) $200\text{−}\mathrm{\AA }$-thick film and (e) $700\text{−}\mathrm{\AA }$-thick film. AFM images of (c) $200\text{−}\mathrm{\AA }$-thick film and (f) $700\text{−}\mathrm{\AA }$-thick as-grown film.

Figure 2

(a) Scattering profiles of the LSMO (001) in the surface normal direction during annealing. The solid lines are the results of fit. (b) $C$-axis lattice spacing as a function of annealing time. The solid line is a guide to the eye.

Figure 3

Temperature dependence of the magnetization of the as-grown and the annealed LSMO films.

Figure 4

Satellite peaks observed near the LSMO (001) peak of the annealed $200\text{−}\mathrm{\AA }$-thick film. The inset shows that the satellite peaks occur at identical in-plane positions.