The transport and magnetic properties of La2/3Ca1/3MnO3(LCMO), (La1−yNdy)Ca1/3MnO3 (y≈0.7, LNCMO), Pr0.7Ca0.3MnO3(PCMO) thin films and LCMO/LNCMO/LCMO (LNL), PCMO/LNCMO/PCMO (PNP) trilayered films were studied. The LCMO thin films exhibit a paramagnetic semiconductor (PS)–ferromagnetic metal (FM) transition around their Curie temperatures (TC∼240 K), but both PCMO and LNCMO thin films display paramagnetic semiconducting behavior down to 60 K, below which the films seem to be ferromagnetic insulators. The zero-field resistance in a trilayered LNL film has an additional peak around 130 K besides the one at 250 K, corresponding to two PS–FM transitions. A similar PS–FM transition is also observed around 110 K in a trilayered PNP film. More than 30% (ΔR/R0) has been obtained in the temperature range 5–300 K for a LNL film at 7 T. These special transport and magnetic properties of trilayers made of manganite perovskites are likely due to the PS–FM transition occurring in the middle LNCMO layer, which is induced by the magnetic coupling between the top and bottom ferromagnetic layers.
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Cheng et al. (1998) studied this question.
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