Large positive magnetoresistance and transport properties of intercalated Cu oxides

Magnetism and electrical resistance as a function of magnetic field, temperature and chemical composition are studied in Cu oxides intercalated with metal phthalocyanines MPc, where M is Fe or Ni, and Pc is C32H16N8. An unusually large positive magnetoresistance (MR) similar to 1200% is observed in FePc-intercalated Bi2Sr2Can-1CunO2n+4 samples with n = 2. The magnitude of MR dropped to 40$ and similar to 0% in the FePc-intercalated n = 3 and n = 4 samples, respectively, and to similar to 300% in the NiPc-intercalated n = 2 sample. The possible mechanism responsible for the observed large MR is tentatively discussed in terms of a competition between the resonant spin-fluctuation and the spin-glass-like states.