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

Wiese N, Dimopoulos T, Ruehrig M, et al. Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB. EPL. 2007;78(6):67002.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 H-sat, behaves like H-sat proportional to H-0 (T/T-0)/sinh(T/T-0) with a characteristic temperature of T-0 approximate to 150 K. Within this model, the Fermi velocity for the Ru laver is of the order of 10(5) m/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 = 2 x 10(3) J/m(3) with a small angular distribution of the anisotropy axes is observed for the AFi trilayers based on amorphous CoFeB alloys. Copyright (C) EPLA, 200

Characterization of embedded MgO/ferromagnet contacts for spin injection in silicon

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n- doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions