Ferrimagnetic charge order in molecular conductors with diluted localized spins exhibiting enhanced giant magnetoresistance effect

In phthalocyanine molecular conductors, the giant magnetoresistance effect is enhanced by the dilution of the localized-spin density. At low spin density, the localized spin induces a random potential for the conduction electron. The charge gap increases as spin density reaches intermediate levels. Analyses based on the mean-field theory and the exact-diagonalization method reveal that the ferrimagnetic charge-ordered state grows above the threshold localized-spin density. The localized spins assist in the ferromagnetic superexchange interaction, consistent with the measured spontaneous magnetization. Various electronic states compete with each other, and the coherent part of the optical conductivity is enhanced by the weak magnetic field. These theoretical findings are in stark agreement with the observed giant magnetoresistance.