ϕ4Domain Walls in Thin Ferromagnetic Films: Occurrence of a Novel Critical Point

We consider the magnetic-field ($H$) dependence of the magnetization ($M$) of a thin low-anisotropy ferromagnetic film near $T_c$ placed on a magnetically hard substrate well below its Curie temperature. Our mean-field-theory analysis uses a free-energy functional analogous to the ${\varphi }^4$ Lagrangian for a complex scalar field used recently in a description of solitons in charge-density-wave condensates. We find a novel critical point in the appropriate $M-H$ plane and comment on its accessibility to experimental investigation.