Preparation, structure, magnetic properties and special magnetoresistance effect of La0.67Sr0.33MnO3+δ/Pr0.7Ca0.3MnO3+δ/La0.67Sr0.33MnO3+δ trilayered thin films

The La0.67Sr0.33MnO3+delta/Pr0.7Ca0.3MnO3+delta/La0.67Sr0.33MnO3+delta(LPL) trilayered films on (100)LaAlO3 substrates are prepared by using direct current (DC) magnetron sputtering method. The results obtained by means of X-ray powder diffractometer show that all films are the high quality epitaxial films. The results gained by SQUID magnetometer indicate that there is a magnetic coupling in the LPL trilayered films. The resistivities of LSMO, PC-MO and LPL films are measured using standard four-probe method and analyzed log-rho-1/T curve. From the results it is concluded that the middle-layered PCMO which is ferromagnetic may play a role of intra-magnetic field, which weakens the paramagnetism of LSMO film, lowers rho(max) and enlarges T-p which is the transition temperature from metal to insulator, just as the applied magnetic field does. And the middle-layered PCMO may induce the change of the density of states in the LSMO' s gap. The two reasons above make the resistivity and T-p of the samples in zero field change with the thickness of PCMO layers.