A method to estimate the critical field for intrinsic spin reversal in tran
sition metals is proposed within the framework of itinerant-electron magnet
ism. By studying the transverse magnetic susceptibility under a Hartree-Foc
k approximation, the dispersion relations of the spin wave excitations are
obtained, which possess a positive gap induced by the anisotropically coupl
ed spin-orbit interaction when the magnetization is along the easy axis. Wh
en a magnetic field applied opposite to the magnetization is strong enough
to overcome the excitation gap, a spin reversal transition takes place whic
h defines the critical field. To illustrate the present method, transition-
metal magnetic monolayers and microclusters have been examined. Comparisons
show that the method can be applied to capture effects missed in the class
ical Stoner treatment. [S0163-1829(99)10101-2].