Raman spectra in epitaxial thin films ofLa1−xCaxMnO3(

Abstract

Raman spectra of LCMO films grown on LAO (001), STO (001), and MgO (001) substrates were studied at different temperatures. The effect of temperature, doping level and strain on Raman spectra are discussed in detail. With decreasing temperature, the changes of Raman spectra are correlated with the disorder-order transition, shuch as: paramagnetism to ferromagnetism, and chargeordering. The strain induced by lattice-substrate mismatch affects the Raman spectra strongly. The mode induced by disorder of oxygen defects is apparently observed in La0.67Ca0.33M nO3 film on STO due to the larger tensile strain. While this mode can not be seen in the Raman spectra for the films on LAO and MgO. A strong unsigned mode at about 690 cm −1 is observed in all films except for La0.67Ca0.33M nO3 film on LAO, which is not observed in bulk sample easily. It suggests that the mode is closely related to the strain.

Strain induced phase separation on La0.5Ca0.5MnO3 thin films

“…It was attributed to a P2 1 /m symmetry superstructure [23] of coexisting orbital and charge ordering or alternatively on two coexisting Pnma phases (FM and AF) with slightly different lattice parameters [55]. On the other hand the new bands are not observed in the other films down to 80 K, neither to LCMO films of a previous study [42]. It seems that strains deactivate the COO phase in all films except LCMO/STO (1 0 0).…”

“…The strain in a film is introduced during preparation from the lattice mismatch and the differences in the thermal expansion coefficient between film and substrate. The similar thermal expansion coefficients of the substrates (b V $ 1 Â 10 À5 K À1 [13]) indicate that the thermally induced strain from the substrates is expected to be approximately the same [42] for all films (b V $ ¼ 3 Â 10 À5 K À1 [52][53][54]). …”

“…The assignment of the GÀpoint modes in LCMO was based on the polarization dependent scattering and previously published theoretical and experimental works on manganites and LCMO (x ¼0.5) [20,39,21,41,40,42]. It is generally accepted that the low frequency bands ðo 1 Þ are mixed R and O(1) vibrations (R-O modes) in the xz plane (A g and B 2g symmetry) or along the y-axes (B 1g and B 3g modes) [20]).…”

“…An extensive amount of Raman data exist for the LCMO series and an assignment for most of the phonons has been proposed [20,39]. In addition, there are detailed studies of the bulk La 0.5 Ca 0.5 MnO 3 compound [21,41,40] but to the best of our knowledge little work has been done on thin films [42].…”

Study on the stability of charge-ordered state and rectifying properties of heteroepitaxial structure for manganites

“…Compared to the conventional semiconductor p-n junctions, the high sensitivity of electronic and magnetic properties of manganites to external magnetic field, electric field, or light assigns them a magnetically or electronically tunable rectifying characteristic [6][7][8]. In this paper, we present a study on the heterojunction composed of La 1-x Ca x MnO 3 (LCMO) (x=1/16, 3/16, 5/16) films and SrTiO 3 crystals doped by 0.5 wt.% Nb (SNTO).…”