Electric, magnetic and THz optical properties of La1-xCaxMnO3 (0.45<x<0.7) and (La1-yPry)0.33Ca0.66MnO3 (0<y<1) thin films

Multiferroic behaviour has been paid a lot of attention due to the rich physics and great potential for technological applications. Recent studies indicate a close correlation between charge ordering (CO) and the ferroelectricity. For this reason we investigate La1-xCaxMnO3 (0.45<x<0.7) and (La1-yPry)0.33Ca0.66MnO3 (0<y<1), which both show competing ferromagnetic metallic and charge ordering insulating phases. The films were grown by metalorganic aerosol deposition technique on MgO(100) substrates. D.c. and a.c. transport (f=0-40MHz), magnetization and optical conductivity, in the THz range of the electromagnetic spectrum, were studied as a function of temperature (5-350K) and magnetic field (0-7T). THz spectroscopy provides a clear sign for the CO transition at 220-280 K, depending on Ca-doping x. Moreover an indication for possible ferroelectricity in half-doped LCMO was observed from d.c. and a.c. transport measurements.