Observation of spin reorientation in layered manganites La 1.2Sr 1.8(Mn 1-yRu y) 2O 7 (0.0⩽ y⩽0.2) by Lorentz transmission electron microscopy

The effect of Ru substitution for Mn in bilayered oxides La _1.2Sr _1.8(Mn _1-yRu _y) ₂O ₇ ( 0⩽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=0 crystal to the c-axis for y=0.2, and it rotates away from the c-axis for the y=0.05 and y=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⩽0.2. Changes in domain size and structure indicate that the uniaxial magnetic anisotropy becomes stronger as Ru content y increases.