Abstract
We determine the range of values of the uniaxial surface anisotropy that leads to the formation of domains in an atomic monolayer of ferromagnetically coupled spins. If the ratio f of to the dipolar energy is larger than a minimum value determined by the ratio of exchange to dipolar energies, and if the easy direction is normal to the layer plane, then a domain pattern is energetically favorable compared to any uniformly magnetized configuration. The maximum component of magnetization normal to the layer, , increases continuously from zero as f increases from its threshold and tends to the saturation magnetization value for large f. Above threshold (f=), the width of the domains is very sensitive to the value of f, increasing very rapidly with f and reaching the macroscopic value of the order of 1 cm for a value f=1.4. Contrary to the usual assumption of thin domain walls determined by the ratio of exchange to anisotropy energy, in monolayers it is necessary to treat the domain structure as a whole and to include explicitly the dipolar energy. A variational treatment gives, at the threshold of , a simple cosine dependence on distance for the magnetization normal to the layer. The calculation is extended to layers consisting of a few atomic planes.
- Received 3 December 1987
DOI:https://doi.org/10.1103/PhysRevB.38.9145
©1988 American Physical Society