Magnetic properties and low-field magnetoresistance of La0.7Sr0.3Mn0.9M0.1O3 compounds (M = Al, Cr, Mn, Fe, Co, Ni, Cu, and Ga)

A systematic study of the Mn-site substitution by M=Al, Cr, Fe, Co, Ni, Cu, and Ga in polycrystalline La0.7Sr0.3Mn0.9M0.1O3 compounds has been carried out. It was deduced from the experimental data that the magnetic coupling between the M and Mn ions is antiferromagnetic for Cr3+ and Fe3+, and ferromagnetic for Co2+/3+, Ni2+, and Cu2+. The variation of the Curie temperature versus M was discussed in terms of the double-exchange (DE) interaction of Mn3+OMn4+ as well as the superexchange interactions between the M and Mn ions. It is found that the Mn-site substitution by various M could not enhance the MR response at a low magnetic field of 2kO.