Measurements of domain-wall energy density for amorphous rare earth-transition metal thin films

The value of domain-wall energy density (σw) has been most often assumed to be proportional to (AxKu)1/2, where exchange stiffness (Ax) is usually calculated from the mean-field theory. We report a simple method to derive σw from the difference between the onset of expanding and collapsing fields (ΔH) for circular domains. A micro-Kerr hysteresis-loop tracer with submicrometer resolution is used to measure the destabilizing field of domains written thermomagnetically in TbFeCo and GdTbFeCo films.