Cs. Arnold et al., Domain formation near the reorientation transition in perpendicularly magnetized, ultrathin Fe/Ni bilayer films (invited), J APPL PHYS, 85(8), 1999, pp. 5054-5059
Ultrathin films with perpendicular magnetization convert from a single doma
in state into a multidomain structure as the reorientation phase transition
to an in-plane magnetization is approached. Reorientation transitions in m
agnetic ultrathin films result from the interplay of interfacial magnetic a
nisotropy, the dipolar interaction, and two-dimensional thermodynamics. The
se transitions can be driven by changing either the film thickness or tempe
rature. Experimental and theoretical studies of this effect are briefly dis
cussed in the context of the thickness-temperature phase diagram of the reo
rientation transition. We then describe magnetic susceptibility experiments
on ultrathin Fe/Ni(111) bilayers. Our experiments indicate an exponential
increase in domain density of a multidomain structure with temperature and
identify the region of the thickness-temperature reorientation transition p
hase diagram where this condensation is most pronounced. The temperature de
pendence of the domain density agrees quantitatively with theoretical predi
ctions. Films that are slightly too thin to exhibit the reorientation trans
ition with temperature are a special case. They undergo a ferromagnetic-to-
paramagnetic transition from the perpendicularly magnetized state and exhib
it domain-like behavior many tens of Kelvin above estimates of the Curie te
mperature. This surprising observation is interpreted using the two-dimensi
onal dipolar Ising model. (C) 1999 American Institute of Physics. [S0021-89
79(99)78408-2].