Towards skyrmion-superconductor hybrid systems

Spin-polarized scanning tunneling microscopy is used to identify the magnetic state of different thin films on a Re(0001) substrate, which becomes superconducting below 1.7 K. All magnetic films contain an Fe/Ir interface, which is known to facilitate the emergence of noncollinear magnetic order. For Fe monolayers on ultrathin Ir films of different thicknesses we find several different atomic-scale magnetic states. For Pd/Fe bilayers we find nanoscale spin spirals as magnetic ground states for Ir thicknesses of three and four atomic layers. In applied magnetic fields skyrmions emerge, and in remanence nontrivial magnetic textures survive. This demonstrates the possibility to prepare skryrmion-hosting magnetic films on superconducting substrates.

Figure 1

Growth and magnetism of Fe on Ir on Re(0001). (a) STM constant-current image (partially differentiated) of a sample with about $0.3\mathrm{AL}$ of Fe deposited onto a sample with about $1.3\mathrm{AL}$ of Ir on Re(0001). The letters $a$ and $b$ indicate different types of Fe/Ir-3 islands. (b) Simultaneously acquired $dI/dU$ map, in which the different layer compositions can be discriminated. (c) STM constant-current image of an $a$-Fe/Ir-3 area; the stripes are of magnetic origin, and the grayscale is 20 pm from black to white. (d) Sketch of the magnetic unit cell (white rectangle) together with a tentative magnetic structure. Measurement parameters: (a), (b) $U=+100\mathrm{mV}, I=1$ nA; (c) $U=+5\mathrm{mV}, I=2\mathrm{nA}$; all: $T=4.2\mathrm{K}$, Cr tip.

Figure 2

Growth and magnetism of $b$-Fe/Ir-3 and Fe/Ir-4 on Re(0001). (a) STM constant-current image (partially differentiated) of a sample with about $0.9\mathrm{AL}$ of Fe deposited onto a sample with about $3.6\mathrm{AL}$ of Ir on Re(0001); the Ir/Re sample before deposition of Fe is shown in Supplemental Figs. S2(c) and S2(d) [23]. (b) Simultaneously acquired $dI/dU$ map, in which the different layer compositions can be discriminated. (c) STM constant-current image (partially differentiated) of the area indicated by the box in (a). (d) STM constant-current image of the indicated Fe/Ir-4 area exhibiting the Néel state; the grayscale is 10 pm from black to white. (e) STM constant-current images of the three different $b$-Fe/Ir-3 areas of (c), which exhibit all possible rotational domains of an atomic-scale roughly square magnetic state; the grayscale is 30 pm from black to white. Measurement parameters: (a), (b) $U=+100\mathrm{mV}, I=1\mathrm{nA}$; (c)–(e) $U=+5\mathrm{mV}, I=4\mathrm{nA}$; all: $T=4.2\mathrm{K}$, Cr tip.

Figure 3

Magnetic field dependence of Pd/Fe/Ir-3 on Re(0001). (a) STM constant-current image (partially differentiated) of a sample with about $0.5\mathrm{AL}$ of Pd on $0.9\mathrm{AL}$ of Fe on $2.6\mathrm{AL}$ of Ir on Re(0001). (b) $dI/dU$ map of the same area in the magnetic virgin state. (c)–(e) $dI/dU$ maps at the indicated magnetic fields, in chronological order. (f) $dI/dU$ map of the central bottom Pd/Fe/Ir-3 island in a different magnetic state in remanence. Measurement parameters: $U=-40\mathrm{mV}, I=1\mathrm{nA}$ [except for (f) with $I=2\mathrm{nA}$], $T=8.6\mathrm{K}$, Fe/W tip without a sign of spin polarization in this measurement.