Magnetic reversal in Dy-doped DyF e 2 / YF e 2 superlattice films

Reversible magnetic exchange springs can be formed in the magnetically soft $\mathrm{YF}{\mathrm{e}}_{2}$ layers of epitaxial $\mathrm{DyF}{\mathrm{e}}_{2}/\mathrm{YF}{\mathrm{e}}_{2}$ multilayer films. Here we show that the insertion of just two monolayers of $\mathrm{DyF}{\mathrm{e}}_{2}$, placed directly in the middle of the $\mathrm{YF}{\mathrm{e}}_{2}$ layers, brings about substantial changes. Results are presented for a Dy-doped (110)-oriented ${[{\mathrm{DyFe}}_{2}(60\AA{})/{\mathrm{YFe}}_{2}(120\phantom{\rule{0.16em}{0ex}}\AA{})/{\mathrm{DyFe}}_{2}(8\phantom{\rule{0.16em}{0ex}}\AA{})/{\mathrm{YFe}}_{2}(120\phantom{\rule{0.16em}{0ex}}\AA{})]}_{15}$ multilayer film, measured at 100 K in fields of up to \ifmmode\pm\else\textpm\fi{}10 T. Using bulk magnetometry, micromagnetic modeling, and Dy-specific x-ray magnetic circular dichroism, it is shown that Dy doping substantially increases the number of spin states available to the system. Altogether 12 distinct spring states are identified which bring additional complexity to the magnetic reversal process. In particular, the exchange springs are no longer reversible, exhibiting magnetic exchange-spring collapse. Full and partial magnetic loops are presented for fields applied along the in-plane easy [001] axis and the in-plane hard $[\overline{1}10]$ axis. In particular, it is demonstrated that exchange-spring collapse is sharpest when the field is applied along a hard in-plane $[\overline{1}10]$ axis.