Neutron and magnetic studies of La sub(0.7) Sr sub(0.3) Mn sub(1-x) Cr sub(x) O sub(3)(x [< or =] 0.7): A homogeneous charge-ordered system

Structural and magnetic properties of La sub(0.7) Sr sub(0.3) Mn sub(1-x) Cr super(x) O sub(3)(0 < x [< or =]0.7) have been studied in order to determine the effect of substitution of Cr super(3+) for Mn super(3+). The data consist of neutron and x-ray powder-diffraction and magnetization measurements. We previously suggested these systems transition from ferromagnetic to antiferromagnetic ordering with the intermediate concentrations containing coexisting ferromagnetic and antiferromagnetic domains. Upon further detailed examination, we find that the neutron data can be fit using a single homogeneous long-range magnetically ordered state and compositionally dependent charge ordering. The magnetic structures are controlled by the competition between Mn-Mn, Mn-Cr, and Cr-Cr interactions (double exchange and superexchange). The metal to semimetal and semimetal to insulator transitions can be quantitatively described as due to the localization effect of superexchange. The presence of charge ordered states in the insulating region arises from the favorable energetics of Mn super(4+)-O-Cr super(3+) superexchange bonds relative to Mn super(3+)-O-Cr super(3+) bonds.