Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB

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 80 K and 600 K. 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 ∝ H0(T/T0)/sinh(T/T0) with a characteristic temperature of T0 ≈ 150 K. Within this model, the Fermi velocity for the Ru layer is of the order of 105 m/s, therefore, explaining the strong variation of the coupling strength with the temperature in Ru-based AFi. Furthermore, a strong uniaxial anisotropy of Ku ≤ 2 × 103 J/m3 with a small angular distribution of the anisotropy axes is observed for the AFi trilayers based on amorphous CoFeB alloys. © Europhysics Letters Association.