Thermomagnetic flux reversal by laser heating in (111) ‐oriented (Gd,Yb)3(Fe,Al)5O12 films and (111) ‐oriented (Gd,Bi)3(Fe,Ga)5O12 films has been investigated theoretically and experimentally. Local switching is governed by wall nucleation and domain wall motion, the first step requiring the most energy. The nucleation threshold strongly depends on the uniaxial magnetic anisotropy and the induced misfit profile due to thermal lattice expansion. The effective uniaxial magnetic anisotropy is found to change sign at certain temperature distributions resulting in spontaneous switching under zero applied field. The size of the domain nucleus is assumed parabolic and depends strongly on the anisotropy field at a given applied field. The temperature distribution in the laser‐heated film volume has been assessed by using the shift of the absorption band edge at 5145 Å wavelength. The present work substantiates the requirement for low‐anisotropy garnet films in thermomagnetic/magneto‐optic memories.
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