Crystal and magnetic structures of (La0.70Ca0.30)(CryMn1-y)O3: a neutron powder diffraction study

The crystal and magnetic structures of La0.70Ca0.30CryMn1 12yO3 for y=0.70, 0.50, and 0.15 have been investigated using neutron powder diffraction. The three samples crystallize in the Pnma space group at both 290 and 5 K and exhibit different magnetic structures at low temperature. In La0.70Ca0.30Cr0.70Mn0.30O3, antiferromagnetic order with a propagation vector k=0 sets in. The magnetic structure is Gx, i.e., of G type with spins parallel to the a axis. On the basis of our Rietveld refinement and the available magnetization data, we speculate that only Cr3+ spins order, whereas Mn4+ act as random magnetic impurities. In La0.70Ca0.30Cr0.50Mn0.50O3 the spin order is still of the type Gx, although the net magnetic moment is smaller. No evidence for magnetic order of the Mn ions is observed. Finally, in La0.70Ca0.30Cr0.15Mn0.85O3 a ferromagnetic ordering of the Mn spins takes place, whereas the Cr3+ ions act as random magnetic impurities with randomly oriented spins