  We present detailed investigations of the magnetic properties of an Fe
monolayer on W and Ta (110) surfaces based on the ab initio screened
Korringa-Kohn-Rostoker method. By calculating tensorial exchange coupling
coefficients, the ground states of the systems are determined using atomistic
spin dynamics simulations. Different types of ground states are found in the
systems as a function of relaxation of the Fe layer. In case of W(110)
substrate this is reflected in a reorientation of the easy axis from in-plane
to out-of-plane. For Ta(110) a switching appears from the ferromagnetic state
to a cycloidal spin spiral state, then to another spin spiral state with a
larger wave vector and, for large relaxations, a rotation of the normal vector
of the spin spiral is found. Classical Monte Carlo simulations indicate
temperature-induced transitions between the different magnetic phases observed
in the Fe/Ta(110) system. These phase transitions are analyzed both
quantitatively and qualitatively by finite-temperature spin wave theory.
