Large Tunable Perpendicular Magnetic Anisotropy in Y3−xTmxFe5O12 ( x = 0–3) Epitaxial Films with Minor Changes in Switching Current

Abstract

We show perpendicular magnetic anisotropy (PMA) in substituted rare-earth iron garnet ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Tm}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (x = 0--3) films epitaxially grown on (111) $({\mathrm{Gd}}_{0.63}{\mathrm{Y}}_{2.37})({\mathrm{Sc}}_{2}{\mathrm{Ga}}_{3}){\mathrm{O}}_{12}$ substrates by magnetron sputtering. With $\mathrm{Tm}$ concentrations varying from x = 0 to x = 3, the effective PMA field of the 10-nm-thick films increases monotonically from 0.3 to 2.7 kOe together with a similar coercivity increase from 2 to 65 Oe. The substituted garnet films with x ranging from 0.6 to 1.2 are structurally much more robust against epitaxial strain relaxation. Magnetotransport measurements in the ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Tm}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$/$\mathrm{Pt}$ heterostructure show that the anomalous Hall effect and spin Seebeck effect are significant and change little with $\mathrm{Tm}$ concentration, indicating that the interface spin-exchange interaction and interface spin-current transmission mainly depend on the net moment of ${\mathrm{Fe}}^{3+}$ sublattices rather than the total moment of ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Tm}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. Importantly, the critical current density for the spin-orbit-torque-induced switching also changes very little with a minor increase from 1.76 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$ to 1.83 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$ A m${}^{\ensuremath{-}2}$. We tentatively attribute this weak PMA-dependent current density to modification of the domain-wall depinning by the current. Our results demonstrate that substituted rare-earth iron garnets can be a general approach to tune PMA within a large range with nearly constant switching current, and yet there is plenty of work left to be done for more efficient SOT-based garnet ferrimagnet spintronics devices.