First-principles study of Co concentration and interfacial resonance states in Fe${}_{1-x}$Co${}_x$ magnetic tunnel junctions

Abstract

The optimal Co concentration in Fe${}_{1-x}$Co${}_x$/MgO magnetic tunnel junctions (MTJs) that maximizes tunneling magnetoresistance (TMR) is still under investigation. We perform a first-principles transport study on MTJs using disordered electrodes modeled using the virtual crystal approximation (VCA) and ordered alloys with various MgO barrier thicknesses. We find that 10-20 Co concentration maximizes TMR using VCA to represent disorder in the electrodes. This TMR peak arises due to a minority d-type interfacial resonance state (IRS) that becomes filled with small Co doping, leading to a decrease in antiparallel conductance. Calculations with ordered Fe${}_{1-x}$Co${}_x$ electrodes confirm the filling of this minority d-type IRS for small Co concentrations. In addition, we construct a 10x10 supercell without VCA to explicitly represent disorder at the Fe${}_{1-x}$Co${}_x$/MgO interface, which demonstrates a quenching of the minority-d IRS and significant reduction in available states at the Fermi level that agrees with VCA calculations. These results explain recent experimental findings and provide implications for the impact of IRS on conductance and TMR in Fe${}_{1-x}$Co${}_x$/MgO tunnel junctions.

13 pages, 10 figures

References in corpus (4)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions
• The fate of topological-insulator surface states under strong disorder
• A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions

Cited by in corpus (1)

• Influence of non-local damping on magnon properties of ferromagnets