Calculations are performed to determine the stable radius of a cylindrically symmetric domain nucleated in magneto-optical films during thermomagnetic writing with a laser beam. A critical bound on domain size is calculated which determines whether or not a domain of given radius, once nucleated, will be stable. The analysis shows that for a ferromagnetic material such as MnAlGe, the domain dimensions can grow beyond the local region of material that is heated above the Curie temperature. For ferrimagnetic thin films having a compensation point Tcomp, stability depends on the difference between ambient and compensation temperatures, ΔT = Ta − Tcomp. With ΔT ≈ 0, wall energy dominates and the critical radius can be calculated from Rc = σ/(2MHc).
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