Bragg-regime diffraction and waveguiding of light by ferromagnetic domains inK2CuF4

Bragg-regime diffraction by a thick magnetic phase grating is observed for the first time at perfectly transparent ferromagnetic stripe domains in ${\mathrm{K}}_2$Cu${\mathrm{F}}_4$ below $T_C=6.2\mathrm{}$ K in the visible region. The diffracted beams are perpendicularly polarized with respect to the incident and the transmitted beam. The diffraction vanishes by virtue of a new waveguiding mechanism owing to total reflection at the spatially thick, but optically thin, domain walls, if the incident light is polarized parallel to the crystalline $a$ axis.