Magnetic and Magneto-transport Properties of (La0.7Ca0.3MnO3)1-x/(Y1Ba2Cu3O7)x Composites

Composites of (La0.7Ca0.3MnO3)(1-x)/(Y1Ba2Cu3O7)(x) [(LCMO)(1-x)(YBCO)(x)], where x is the mole fraction, were prepared by using the conventional solid-state reaction to understand the effects of YBCO addition on the magnetoresistance (MR,) of the composite. (LCMO)(1-x)(YBCO)(x) is identified as a two-phase composite of ferromagnetic manganite and a high-T-C superconductor by X-ray diffraction and scanning electron microscopy. The temperature dependence of the resistivity shows that the transport behavior of the composites is governed by the grain boundaries. According to the doping content, the positive MR of the YBCO phase dominates the negative MR of the LCMO phase, which gives rise to an enhancement of the magnetic inhomogeneity and a suppression of the double exchange interaction. The sign of the MR, for the composite depends on magnetic field and the doping content. A tuning between positive and negative MR. by means of the magnetic field can be made to be the field-sensitive tuning of the MR.. The field-sensitive MR is due to the coexistence of positive and negative MR and results from the proximity effect between LCMO and YBCO grains.