Magnetic impurity effect on charge and magnetic order in doped La _1.5Ca_0.5CoO₄

Neutron scattering experiments were performed on single crystals of magnetic impurity doped cobalt oxides La_1.5Ca_0.5CoO ₄ to characterize the charge and spin orders. We newly found contrasting impurity effects. Two types of magnetic peaks are observed at q=(0.5,0,L) with L=half-integer and integer in La_1.5Ca _0.5CoO₄, while magnetic peak at L=half-integer (integer) was only observed in Mn (Fe)-substituted sample. Although Mn and Fe impurities degrade charge and magnetic order, Cr impurity stabilizes the ordering at x=0.5. Based on the crystal structural analysis of Cr doped sample, we found that the excess oxygen and change of octahedron around Co³⁺ were realized in Cr doped sample.