Abstract
La0.92Sr0.08MnO3 films with the thickness (t) ranging from 8 to 157 nm, grown on (001)-oriented SrTiO3 substrates by rf magnetron sputtering, undergo a secondary metal-insulator transition (SMIT) below a critical temperature when t >= 63 nm. The transition temperature gradually increases from 25 K at 63 nm to 108 K at 157 nm with increasing film thickness. Raman spectra demonstrate that the occurrence of the SMIT is attributed to the reduction of the Jahn-Teller distortion. Further investigations indicate that the SMIT can take place in the ferromagnetic (63 nm <= t < 98 nm) and A-type antiferromagnetic (t >= 98 nm) spin structures, which is ascribed to the generation of two-dimensional conduction bands in the MnO2 planes through the double-exchange interaction. This work suggests that the SMIT provides a pathway to study multiple metal-insulator transitions and demonstrates the potential applications in spintronic devices.