Exchange coupling and noncollinear magnetic states in Ni/Fen/Ni(1 0 0) multilayers

• First-principles study of Ni/Fe/Ni multilayers with variable Fe spacer thickness.
• AFM Ni interlayer exchange coupling (IEC) for 3 and 4 Fe MLs, FM for 5 MLs.
• Noncollinear Fe magnetism for 3 & 4 Fe MLs for constrained FM Ni magnetization alignment.
• Noncollinear spin configuration and IEC of 1st excited state in Ni/3ML-Fe/Ni trilayer.
• Noncollinearity explained by the ground state of bulk fcc Fe and imposed constraints.

The Ni interlayer exchange coupling (IEC) and the atomic-scale magnetic configurations in fcc Ni/Fen/Ni(100) multilayers, with ultrathin Fe spacers, are investigated using first-principles density-functional theory including the noncollinear spin formalism. The trends with changing Fe thickness (n  ) between 3 and 5 monolayers (MLs) are examined. For n=3n=3 and 4 MLs, we find the ground state to display antiferromagnetic IEC between the Ni films, while for the 5-ML Fe spacer, the IEC changes into ferromagnetic. Upon reversal of the magnetization alignment, from antiparallel to parallel, between the Ni films with 3- and 4-ML thick Fe spacer, we find noncollinear magnetic configurations in the Fe layer as the lowest-energy states, which are related to the magnetic instability towards noncollinear solutions in bulk γγ-Fe.

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