Interlayer exchange coupling in Pt/Co/Ru and Pt/Co/Ir superlattices

Magnetic multilayer thin films with perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii-Moriya interaction (iDMI) are of intense interest for realizing magnetic skyrmions and modifying topological spin textures. We systematically investigate interlayer exchange coupling (IEC) in Pt/Co/Ru(Ir) superlattices that have PMA and large iDMI. The IEC is greatly tunable by varying Ru(Ir) or Pt thickness and the antiferromagnetic IEC is as large as $1.3\mathrm{mJ}/{\mathrm{m}}^2$ that is on the same order of magnitude as the iDMI. We find unusual magnetic hysteresis loop crossing between field-ascending and -descending magnetization curves. Furthermore, we identify magnetic phase diagrams for antiferromagnetic IEC and hysteresis loop crossing with respect to Ru(Ir) and Pt thickness. Our experimental findings may open a way in the development of synthetic antiferromagnetic spintronics and/or the realization of antiferromagnetic skyrmions.

Figure 1

Schematic diagram of Pt/Co/Ru(Ir) multilayer with PMA, iDMI, and IEC.

Figure 2

X-ray reflectivity as a function of 2θ for ${\left[\mathrm{Pt}\left(10\right)/\mathrm{Co}\left(8\right)/\mathrm{Ru}\left(7\right)\right]}_{10}$ superlattice. (b) Normalized Hall resistance of ${\left[\mathrm{Pt}\left(10\right)/\mathrm{Co}\left(8\right)/\mathrm{Ru}\left(7\right)\right]}_{10}$ superlattice as a function of magnetic field for field descending (solid black squares) and ascending (solid red circles), respectively. Blue up (red down) arrows indicate moments pointing up (down).

Figure 3

(a)–(e) Normalized Hall resistance of ${\left[\mathrm{Pt}\left(10\right)/\mathrm{Co}\left(8\right)/\mathrm{Ru}\left(\mathrm{wedge}\right)\right]}_{10}$ superlattices as a function of magnetic field for field descending (solid black squares), field ascending (solid red circles), and minor loop (open blue triangles), respectively. Inset of (e) is for sample ${\left[\mathrm{Pt}\left(10\right)/\mathrm{Co}\left(10\right)/\mathrm{Ru}\left(23.8\right)\right]}_{10}$. (f) Normalized Hall resistance loop for ${\left[\mathrm{Pt}\left(\mathrm{wedge}\right)/\mathrm{Co}\left(8\right)/\mathrm{Ru}\left(7\right)\right]}_{10}$ with Pt thickness of 5.9 Å.

Figure 4

Magnetic phase diagrams for (a) ${\left[\mathrm{Pt}/\mathrm{Co}/\mathrm{Ru}\left(\mathrm{wedge}\right)\right]}_N$, (b) ${\left[\mathrm{Pt}\left(\mathrm{wedge}\right)/\mathrm{Co}\left(8\right)/\mathrm{Ru}\left(7\right)\right]}_{10}$, and (c) ${\left[\mathrm{Pt}/\mathrm{Co}/\mathrm{Ir}\left(\mathrm{wedge}\right)\right]}_N$ superlattices. Dashed lines are guides to the eyes.