THE SPECIAL MAGNETORESISTIVE EFFECT IN TRILAYERED FILMS MADE OF MANGANITE PEROVSKITES

The transport and magnetic properties of La2/3Ca1/3MnO3(LCMO), (La1-yN dy)Ca1/3MnO3 (y approximate to 0.7, LNCMO), Pr0.7Ca0.3MnO3(PCMO) thin films and LCMO/LNCMO/LCMO (LNL), PCMO/LNCMO/PCMO (PNP) trilayered film s were studied. The LCMO thin films exhibit a paramagnetic semiconduct or (PS)-ferromagnetic metal (FM) transition around their Curie tempera tures (T-C similar to 240 K), but both PCMO and LNCMO thin films displ ay paramagnetic semiconducting behavior down to 60 K, below which the films seem to be ferromagnetic insulators. The zero-field resistance i n a trilayered LNL film has an additional peak around 130 K besides th e one at 250 K, corresponding to two PS-FM transitions. A similar PS-F M transition is also observed around 110 K in a trilayered PNP film. M ore than 30% (Delta R/R-0) has been obtained in the temperature range 5-300 K for a LNL film at 7 T. These special transport and magnetic pr operties of trilayers made of manganite perovskites are likely due to the PS-FM transition occurring in the middle LNCMO layer, which is ind uced by the magnetic coupling between the top and bottom ferromagnetic layers. (C) 1998 American Institute of Physics. [S0003-6951(98)04019- 4].