CONICAL BUBBLES

In magnetic garnet films with perpendicular anisotropy, cylindrical do mains called bubbles are well known characteristic domain structures. Using the anisotropic dark field technique in an optical microscope, w e have investigated the bubble wall contrast as well as that of vertic al Bloch lines contained in them. It is found that bubbles have in fac t a slightly conical shape, with a tilt of the order of degrees, depen ding in sign and magnitude on the sample. We interpret it as a consequ ence of a variation in the sample parameters along its thickness. A nu merical evaluation of tilt is proposed in the case of a gradient of wa ll energy density. Also, a simplified optical calculation of light dif fraction at a wall is presented and is used for fitting experimental d ata.