Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Thermodynamic properties, in particular, the temperature dependencies of magnetization of asymmetrically sandwiched ultrathin cobalt films with perpendicular anisotropy are investigated. The experimental results are described theoretically in the frame of magnon thermodynamics consistently accounting for the finite thickness of the films. The analysis includes both three-dimensional (Bloch’s T3/2 law) and two-dimensional (the 2D Bloch law) theories as limiting cases. By fitting the experimental temperature dependencies of magnetization to the theoretical model, the exchange stiffness parameter is extracted. This approach provides access to the exchange stiffness without the need to know the strength of the Dzyaloshinskii-Moriya interaction in the stack. The exchange stiffness of sub-nm-thick Co films is found to be about three times smaller compared to the case of bulk cobalt. In the temperature range T<170±30 K the temperature dependencies of magnetization follow the 2D Bloch law. The applicability of Bloch’s T3/2 law and analysis of the Curie temperature (two-dimensional and three-dimensional pictures) to extract the exchange stiffness for sub-nm-thick Co films are tested as well. The closest value of the exchange stiffness to the magnon thermodynamics turned out to be within the analysis of the Curie temperature in the three-dimensional picture.