Source and origin of the interfacial Dzyaloshinskii-Moriya interaction in a heavy-metal|magnetic-insulator bilayer

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) was observed in the bilayer consisting of a heavy metal and a ferromagnetic insulator such as $\mathrm{Pt}|{\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TIG), but the source and origin are still controversial. Here, we quantitatively investigate the iDMI strength in Pt|TIG by inserting a thin ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ layer and/or a thin Cu layer between Pt and TIG. Our results suggest the iDMI contributed by both the Pt|TIG and the TIG|substrate interfaces. At the Pt|TIG interface, we find that Pt is essential for the strong iDMI. The disentangled iDMIs for Fe-Fe and Tm-Fe pairs are comparable, revealing that the Tm ions provide not only an additional Tm-Fe iDMI, but also the spin-orbit coupling to enhance the iDMI. At the TIG|substrate interface, the iDMI is attributed to the lattice-mismatch-induced deformation of the electron cloud for the ferromagnetic ions.

Figure 1

(a) High-resolution XRD patterns for TIG (6.5 nm)|SGGG, YIG (0.9 nm)|TIG (6.5 nm)|SGGG, and YIG (9.0 nm)|SGGG. (b) Representative two-dimensional topography of the TIG surface characterized by AFM. The out-of-plane hysteresis loops at 300 K for (c) TIG(6.5 nm)|SGGG and (d) YIG(0.9 nm)|TIG(6.5 nm)|SGGG.

Figure 2

The SH-AHE curves at 300 K for (a) Pt (3 nm)|TIG (6.5 nm)|SGGG and (b) Pt (3 nm)|YIG (0.9nm)|TIG (6.5 nm)|SGGG with $H$ along the $z$-axis. (c) The geometry for electrical transport measurements. Normalized ${\mu }_0{H}_n$ as a function of ${\mu }_0{H}_{in}$ for Pt (3 nm)|TIG (6.5 nm)|SGGG and Pt (3 nm)|YIG (0.9 nm)|TIG (6.5 nm)|SGGG measured at (d) 300 K and (e) 200 K. The black curves are the fitting results based on the extended droplet model. (f) Temperature dependence of $D_s$ for Pt|TIG|SGGG and Pt|YIG|TIG|SGGG.

Figure 3

Normalized ${\mu }_0{H}_n$ as a function of ${\mu }_0{H}_{in}$ for Pt (3 nm)|Cu (1.2 nm)|TIG (6.5 nm)|SGGG and Pt (3 nm)|Cu (1.2 nm)|YIG (0.9 nm)|TIG (6.5 nm)|SGGG measured at (a) 300 K and (b) 200 K. The black curves are the fitting results based on the extended droplet model. (c) Temperature dependence of $D_s$ for Pt|Cu|TIG|SGGG and Pt|Cu|YIG|TIG|SGGG and $\mathrm{\Delta }{D}_s^{\mathrm{Cu}|\mathrm{T}-\mathrm{Y}}.$

Figure 4

(a) Temperature dependence of $D_s$ for $D_s^{\mathrm{Pt}|\mathrm{TIG}}, D_s^{\mathrm{TIG}|\mathrm{sub}}, D_s^{\mathrm{Pt}|ad},$ and $D_s^{\mathrm{Pt}|cd}$ in Pt|TIG|SGGG. (b) Schematic diagram of the structural symmetry at the YIG|TIG interface for the interfacial ${\mathrm{Fe}}_d$.