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

We report the study on the stability of charge-ordered (CO) state and rectifying properties of heteroepitaxial structure for manganites R1-xCaxMnO3 (R = La, Pr, and Sm) by measuring magnetoresistance, magnetization, specific heat, I−V characteristics, and X-ray diffraction. For the La1-xCaxMnO3 system, near the Ca2+concentration of x = 0.75 the CO state is mostly stabilized and insensitive to external magnetic fields, which is supported by the charge transport, magnetic, and specific heat properties. By analyzing powder X-ray diffraction patterns, we found that the Jahn–Teller (JT) distortion in the CO state is the largest at x = 0.75, which confirms the close relationship between the JT lattice distortion and the stability of the CO state for La1-xCaxMnO3. The stability of the CO state is also related to the A-site average ionic radius, 〈rA〉. With decreasing the radius of the doped rare-earth elements (La, Pr, and Sm), the most stable CO state for the each doped system shifts gradually toward lower Ca2+concentration. In addition, we have fabricated simple p–n junctions using a heteroepitaxial structure of La1-xCaxMnO3/Nb-doped SrTiO3. These junctions show good rectifying properties for temperature from 85 to 305 K. The photovoltage as a function of light wavelength at room temperature has also been studied and the maximum photovoltage can reach 180 mV. The good rectifying behaviors and strong photovoltaic effect make these simple p–n junctions promising for applications.