Large magnetoresistance and charge transfer between the conduction and magnetic electrons in layered oxyselenide BiOCu0.96Se

Abstract

The electrical and magnetic properties of slightly Cu-deficient BiOCu_0.96Se have been investigated using neutron and X-ray diffraction, ac magnetic susceptibility, magnetization and electric resistivity measurements. The layered BiOCu_0.96Se crystallizes into a tetragonal lattice with a P4/nmm symmetry. Thermal profiles of the electrical resistivity reveal a semiconductor type behavior, but depart from its course at low temperatures when antiferromagnetic coupling becomes thermally loosened at 140 K. Positive magnetoresistances are obtained at all temperatures studied. With an applied magnetic field of 0.5 kOe, the magnetoresistance reaches 235% at 2 K. It decreases with increasing temperature, but stabilizes to 70% above 60 K. Both ferromagnetic and antiferromagnetic coupling are detected between the Cu spins in the SeCu₄ pyramidal blocks, which results in a non-collinear spin arrangement at low temperatures. The antiferromagnetic component becomes disordered above T_N = 140 K, whereas the ferromagnetic moment persists up to T_C = 300 K. Interlayer charge transfer between the conduction and magnetic electrons gives rise to an anomaly in the magnetic order parameter.