Magnetic response in granular La1.85Sr0.15CuO4 and its composites with a second-phase, nanocrystalline La0.9Sr0.1MnO3 or LaNiO3 were systemically investigated. The results show a pronounced magnetic suppression of superconductivity, which can be significantly modified by the magnetic behavior of the second-phase grains. The superconductive coherence, weak-link and tunneling processes within and between the superconductive grains can be drastically suppressed by the ferromagnetic La0.7Sr0.3MnO3 grains. Under low applied fields, this suppression may be further enhanced by the inductive field generated from the ferromagnetic neighbor. In total, from this suppression, a large tunable low field sensitive positive magnetoresistance as reported previously is generated. (c) 2006 Elsevier B.V. All rights reserved.