Preparation, structure, magnetic properties and special magnetoresistance effect of La0.67Sr0.33MnO3+delta/Pr0.7Ca0.3MnO3+delta/La0.67Sr0.33MnO3+delta 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 cu rrent (DC) magnetron sputtering method. The results obtained by means of X- ray powder diffractometer show that all films are the high quality epitaxia l films. The results gained by SQUID magnetometer indicate that there is a magnetic coupling in the LPL trilayered films. The resistivities of LSMO, P C-MO and LPL films are measured using standard four-probe method and analyz ed log-rho-1/T curve. From the results it is concluded that the middle-laye red PCMO which is ferromagnetic may play a role of intra-magnetic field, wh ich 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 cha nge 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 thick ness of PCMO layers.