Exploration of magnetic order in Pr0.5Ca0.5CoO3δ (δ=0) below the metal-insulator transition

We have investigated the low temperature magnetic state of Pr0.5Ca0.5CoO3−δ with (δ=0) by means of resistivity, dc magnetization, susceptibility, magnetotransport and neutron diffraction. We find that below the metal-insulator transition (MIT) this system can be described as a paramagnetic insulator with dominant ferromagnetic interactions between Co atoms. In this regime, it presents a considerable negative magnetoresistance (20%–40%), while above MIT the magnetoresistance is negligible or even slightly positive. Neutron diffraction measurements reveal that there is no long-range ferromagnetic (FM) or antiferromagnetic (AFM) order. These results are in contradiction with the spin state picture previously drawn for this system.