The magnetic anisotropy in ${\mathrm{Fe}}_x{\mathrm{Co}}_{100-x}/\text{MgO}/{\mathrm{Fe}}_x{\mathrm{Co}}_{100-x}$ magnetic tunnel junctions as a function of composition is investigated on different substrates (Cu, Ag, and MgO). We use the full relativistic screened-Korringa-Kohn-Rostoker method and employ the coherent potential approximation for description of the alloys. Our findings show that the magnetocrystalline anisotropy (MCA) strongly depends on the CoFe composition and that the MCA decreases with increasing Co concentration. At a certain composition there is a transition at which the MCA changes sign from positive to negative. The origin of the MCA is related to the difference of density of states between $d$ orbitals around Fermi energy, in particular, the difference between $d_{yz}\left(d_{zx}\right)$ and $d_{3z^2-r^2}$ orbitals. We also calculate the shape anisotropy in order to obtain phase diagrams that show at which magnetic layer thickness and at which composition we expect perpendicular anisotropy.

• Received 28 August 2014
• Revised 22 October 2014

DOI:https://doi.org/10.1103/PhysRevB.90.184409