  The temperature dependence of saturation and spin-flop fields for artificial
ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has
been investigated in a temperature range between 80K and 600K. The results
presented in this paper are relevant for magnetic devices using this system,
e.g. magnetic-random access memory based on spin-flop switching. In good
accordance to the theory, the saturation field Hsat behaves like Hsat ~ H_0
(T/T_0)/sinh(T/T_0) with a characteristic temperature of T_0 = 150K. Within
this model, the Fermi velocity for the Ru layer is of the order of 10^5m/s,
therefore, explaining the strong variation of the coupling strength with the
temperature in Ru based AFi. Furthermore, a strong uniaxial anisotropy of K_u =
2x10^3 J/m^3 with a small angular distribution of the anisotropy axes is
observed for the AFi trilayers based on amorphous CoFeB alloys.
