Observation of spin reorientation in layered manganites La1.2Sr1.8(Mn1−yRuy)2O7 (0.0⩽y⩽0.2) by Lorentz transmission electron microscopy

The effect of Ru substitution for Mn in bilayered oxides La1.2Sr1.8(Mn1−yRuy)2O7 (0⩽y⩽0.20⩽y⩽0.2) was investigated by magnetization measurements and low-temperature Lorentz transmission electron microscopy. It was found that the magnetic anisotropy is controlled by the Ru content y and temperature T. The easy axis changes from 〈1 1 0〉 for the y=0y=0 crystal to the c  -axis for y=0.2y=0.2, and it rotates away from the c-  axis for the y=0.05y=0.05 and y=0.07y=0.07 crystals with decreasing temperature. Furthermore, maze-shaped magnetic domain structures were observed in the (0 0 1) thin crystals with 0.05⩽y⩽0.20.05⩽y⩽0.2. Changes in domain size and structure indicate that the uniaxial magnetic anisotropy becomes stronger as Ru content y increases.