CONICAL BUBBLES

In magnetic garnet films with perpendicular anisotropy, cylindrical domains called bubbles are well known characteristic domain structures. Using the anisotropic dark field technique in an optical microscope, we have investigated the bubble wall contrast as well as that of vertical Bloch lines contained in them. It is found that bubbles have in fact a slightly conical shape, with a tilt of the order of degrees, depending in sign and magnitude on the sample. We interpret it as a consequence of a variation in the sample parameters along its thickness. A numerical evaluation of tilt is proposed in the case of a gradient of wall energy density. Also, a simplified optical calculation of light diffraction at a wall is presented and is used for fitting experimental data.