Microscopy of magnetic transition in a layered manganite ${\mathrm{La}}_{2-2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_2{\mathrm{O}}_7$ $(x=0.32)$

Temperature-dependent magnetic structures in ${\mathrm{La}}_{2-2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_2{\mathrm{O}}_7$ $(x=0.32)$ are derived from real-space observation based on three-dimensional magnetization vector analysis using spin-polarized scanning electron microscopy. Below $80\mathrm{K}$, a flux closure structure is formed at the $ab$ surface, indicating ferromagnetic inter-bilayer coupling with magnetization along the $c$ axis. The closure domains are turned into larger ones with irregular shapes above $80\mathrm{K}$. The drastic domain reconstruction results from the change in inter-bilayer coupling to antiferromagnetic one, accompanied by the magnetization inclined toward the $ab$ plane.