Substrate‐Dependent Anisotropy and Damping in Epitaxial Bismuth Yttrium Iron Garnet Thin Films

Abstract

Iron garnets that combine robust perpendicular magnetic anisotropy (PMA) with low Gilbert damping are desirable for studies of magnetization dynamics as well as spintronic device development. This paper reports the magnetic properties of low‐damping bismuth‐substituted iron garnet thin films (Bi0.8Y2.2Fe5O12) grown on a series of single‐crystal gallium garnet substrates. The anisotropy is dominated by magnetoelastic and growth‐induced contributions. Both stripe and triangular domains form during field cycling of PMA films, with triangular domains evident in films with higher PMA. Ferromagnetic resonance measurements show damping as low as 1.3 × 10−4 with linewidths of 2.7 to 5.0 mT. The lower bound for the spin‐mixing conductance of BiYIG/Pt bilayers is similar to that of other iron garnet/Pt bilayers.

Damping and Interfacial Dzyaloshinskii–Moriya Interaction in Thulium Iron Garnet/Bismuth-Substituted Yttrium Iron Garnet Bilayers

“…The large paramagnetic nonlinear signal of the GSGG and NGG substrates prevented background subtraction for the in-plane hysteresis loops of the films. The saturation magnetization of these films is in the range of 80–105 kA/m at room temperature, comparable to TmIG (90–120 kA/m) , and BiYIG films (125–145 kA/m) . Both BiYIG and TmIG have negative λ 111 and an in-plane tensile strain so that the magnetoelastic anisotropy favors PMA.…”

“…Fits to the Kiessig fringes for the bilayered film indicate that the thicknesses of the BiYIG layer and TmIG layer are 4 and 3.5 nm, respectively. Prior work has shown, based on reciprocal space map measurements performed on BiYIG, TmIG, and terbium iron garnet (TbIG) epitaxial films deposited on garnet substrates, that such garnet films are fully strained in-plane to match the substrate lattice parameter for the thickness of 70, 20, and 90 nm, respectively. Since all the BiYIG films, bilayered films, and codeposited films used in this study have thicknesses lower than 21 nm, we expect that they are all coherently lattice-matched to the substrate.…”

“…The linear fits obtained from Δ H ( f ) and the corresponding damping values for various bilayer and codeposited films are shown in Figure . The data for a 70 nm thick BiYIG film deposited on a GSGG substrate from our previous work has been included for comparison . Damping and Δ H 0 values for bilayered and codeposited films from this study are displayed in Table .…”

“…Instead, epitaxial BiYIG can be grown with PMA on garnet substrates with higher lattice parameters than GGG by exploiting a combination of magnetoelastic and growth-induced anisotropies. 44,45 The Gilbert damping of BiYIG films is 1.3 × 10 −4 −5.6 × 10 −4 , an order of magnitude higher than that of YIG but much lower than that of REIGs with strong spin−orbit coupling. [10][11][12]14,44 For example, the damping of TmIG films is around 0.02.…”

“…Yttrium iron garnet (Y 3 Fe 5 O 12 , YIG) has the lowest known Gilbert damping, as low as 10 –5 in bulk. ,, However, the growth of high-quality YIG films with PMA has been challenging, despite several demonstrations of epitaxial − and polycrystalline PMA YIG films. Instead, epitaxial BiYIG can be grown with PMA on garnet substrates with higher lattice parameters than GGG by exploiting a combination of magnetoelastic and growth-induced anisotropies. , The Gilbert damping of BiYIG films is 1.3 × 10 –4 –5.6 × 10 –4 , an order of magnitude higher than that of YIG but much lower than that of REIGs with strong spin–orbit coupling. − ,, For example, the damping of TmIG films is around 0.02. ,, While the low damping of BiYIG films enables fast domain wall dynamics, BiYIG films exhibit no DMI and SOT-driven domain wall motion can be achieved only in the presence of an in-plane magnetic field. , …”