Exchange spring switching in Er-dopedDyFe2/YFe2magnetic thin films

Reversible magnetic exchange springs can be formed in multilayer films, grown by molecular beam epitaxy. Here we demonstrate that small amounts of anisotropic ${\mathrm{ErFe}}_{2}$, placed in the middle of the ${\mathrm{YFe}}_{2}$ magnetic exchange springs, can bring about substantial changes. Results are presented for an Er-doped (110)-oriented multilayer film, at 100 K in fields of up to $\ifmmode\pm\else\textpm\fi{}14$ T. Using both Er and Dy-specific soft x-ray magnetic circular dichroism and micromagnetic modeling, it is demonstrated that Er doping gives rise to (i) noncollinear exchange spring states in zero field, (ii) magnetic exchange spring collapse, (iii) a marked increase in the number of different exchange spring states available to the system, and (iv) strikingly different Er and Dy magnetization loops. Full and partial loops are presented for both the in-plane hard and easy axes. The magnetization loops for Dy sublattice show that at least ten different exchange spring states are accessed during magnetic reversal. Magnetic switching scenarios, involving mixtures of N\'eel-like and Bloch-like domain walls, are presented and discussed.