The transport properties in the La2/3(Ca1-xSrx)1/3MnO3 (x=0, 1/3, 2/3) films prepared using the RF magnetron sputtering method were investigated. The effect of the Ca, Sr double-doping at the A position in the La2/3A1/3 MnO3 on the structure of the targets and transport of the films has been studied. With the increase of x, the structures of the targets transform from the rhombohedral phase to the cubic phase; the metal-insulator phase transition temperature(Tp) of the films increases; and the corresponding peak resistivity decreases. All the phenomena can be qualitatively explained by the lattice effect.

Using pulsed laser deposition method, the heavy double-doped La1/3(Ca2/3Sr1/3)2/3MnO3 (LCSMO) thin film was epitaxially prepared on LaAlO3 (012) single crystal substrate. The structure and transport properties of the film were investigated. The results indicate that the film is perovskite pseudocubic structure, and the surface is relatively smooth. The electrical transport property of the film was determined using the DC four-probe method. The results exhibit semiconducting behavior, and no metal–insulator transition temperature TMI of the film in the temperature range of 77–400K. This character was explained by the MnO6 octahedron, which is distorted with heavy concentration.

A Ca, Sr double-doped La 2/3 (Ca 2/3 Sr 1/3 ) 1/3 MnO 3 thin film with a thickness of about 60~nm was deposited on (100) LaAlO 3 substrates using the RF magnetron sputtering method from the bulk compound prepared using the solid-state reaction method. The experimental results show that a phase transition from the ferromagnetic metallic state to the paramagnetic insulating state occurs at 341 K (near to T p , the highest peak temperature). The R–T curve deviation of the thin film with the application of CW laser is dramatic in the low-temperature range and Δ R/R is positive. At 276 K, the Δ R/R reaches the maximum, about 41 %, and the temperature of the photo-induced resistance maximum of this double-doped thin film appears near to room temperature range, which offers a new method for the application of CMR photo-electric devices.PACS Nos.: 78.66.–w, 81.07–b

Photo-responsive properties studied in perovskite manganese La2/3(Ca3/4Sr1/4)1/3MnO3 (LEMO) thin film with continued laser and modulated laser pulses are studied in this paper. The two valence alkaline earth elements make the Mn have two states: Mn3+(t32geg) and Mn4+(t32g). The Sr, Ca double-doped holes concentration is from 0.2 to 0.4 with maintained electric charge balance. The resistivity and temperature principle indicates that the material has CMR effect and transforms characteristics from metal to semiconductor and insulator. The results show that the phase transition from ferromagnetic metallic state to paramagnetic insulating state occurs at 341 K while the highest peak temperature is near to Tp. The maximizing photo-responsive resistivity change (ΔR/R0)max can reach 43.7%. Responsive signal intensity to the laser pulse has nonlinear relationships with the temperature and bias current. The photo-response resistivity changes with excited down-spin electrons and the exciting field. The optimum photo-responsive condition is T = 229 K, I = 24.7 mA. (ΔR/R0)max increases with temperature following exponential characteristic and there is a limited temperature for photo-response. The carrier electrons and small polarons have effects on thephoto-responsive characters.

In this paper, deposition of La-2/3(Ca1/3Sr2/3)(1/3)MnO3 thin films with femtosecond high repetition rate laser (1kHz) and low repetition rate nanosecond KrF laser (several Hz) are described. The X-ray diffraction pattern shows that the film has crystal plane orientation (100) on the LAO substrate and epitaxtial single crystal structure, and the composition analysis shows that the atomic percentage of Sr and Ca in the film is in good agreement with the target composition. The characteristics of the resistance with temperature is discussed.

The thin films of La2/3(Ca1−xSrx)1/3MnO3 (LCSMO) with x=0, 1/3, and 2/3 through the Ca, Sr double-doping at A site of the La2/3A1/3MnO3 were prepared using the RF magnetron sputtering method. The X-ray diffraction patterns of the bulk samples show that with the increase of x, the structures exhibit the transition from the rhombohedral phase to the pseudo-cubic phase. The electrical properties show that these three thin films are the ferromagnetic and metallic state which can be fitted into the single magneton scattering formula: ρ(T)=ρ0+aT2 at low temperature. The temperature range of the ferromagnetic metallic state becomes larger, and the peak resistivity temperature (Tp) increases with x. These can be qualitatively explained by the double exchange model.

Using pulsed-laser deposition method, the heavy and double-doped La-1/3(Ca2/3Sr1/3)(2/3)MnO3 (LCSMO) thin film was epitaxially prepared on LaAlO3 (012) single crystal substrate. The structure of the film studied by X-ray diffractometry shows the film has perovskite pseudocubic structure, and is of preferential orientation (012). The morphology studied by atomic force microscopy shows the surface of the film is relatively smooth. A transport property of the thin film in a closed-circuit liquid nitrogen cryostat was determined using the four-probe method. The temperature dependence of resistance exhibit a semiconducting behavior, and no metal-insulator transition temperatures T-MI of the film in the temperature range of 77 K similar to 400 K. And the infrared transmission spectrum indicates there is a strong absorption peak at k=606 cm(-1), and from this the optical energy gap is about 0.7 eV. and the optical refractive index is 1.373. Author suggest these properties are caused by the lattice distortion caused by the different A-site radius.

Photo-induced resistivity change p has been studied in perovskite manganite La2/3Ca1/3MnO3 thin films with a continous wave laser and modulated laser pulses in this paper. Experimental results show that in the sample films, the maximum of photo-induced resistivity change（ΔR/R）max can reach 43.5%,which is a very exciting figure in this research field. Modulated laser pulse induced signal intensity has a highly nonlinear relation with the applied current and temperature. The maximum of photo-induced resistivity increase is a second power function of the applied current, while the temperature at which the maximum appears is proportional to the bias current. There exist an optimal bias current and a temperature for optical response in this film. These results are attributed to the optical excited eg↓ carriers and polarons.

The transient resistance change induced by modulated laser pulse has been observed in the double-doped perovskite La2∕3(Ca1∕3Sr2∕3)1∕3MnO3 thin film prepared by rf magnetron sputtering method. The time response character of photoinduced voltage signal is independent of the bias current, but its photoinduced relative change in resistance is nonlinearly dependent on the bias current. All the phenomena in the perovskite film is explained by the double exchange model and the small polaron theory. This is very important in the practical application of a colossal magnetoresistance photoelectric switch.