Magnetism of the Gd(0001) surface revisited: DMI, Frustrating Exchange, Strain

There is a long standing effort of the scientific community to understand the magnetism of the Gd(0001) surface that produced over time a lot of scientific insights with partly contradictory results. Combining spin-polarized scanning tunneling microscopy (SP-STM) investigations on thickness-dependent domain structures of Gd/W(110) with first-principles investigations based on density functional theory (DFT) we reach a converging picture. Here we report on the observation of a DMI-driven spin-spiral state at the surface of epitaxial Gd(0001) films grown on W(110). We confirmed the existence of a spin reorientation transition (SRT) [1] from in-plane to out-of-plane magnetized films at a critical thickness Θ_crit ≈100 +- 20 AL [2]. In the vicinity of this SRT, by means of SP-STM we identify striped regions with a periodicity of about 2 nm. The application of an external magnetic field induces a rearrangement of the stripes, thereby unambiguously confirming its magnetic origin. We explain the results as a combination of the Dzyaloshinskii-Moriya interaction (DMI) [3,4] and the competing exchange interaction at the Gd surface whose competition is controlled by strain.

[1] A. Berger et al., Phys. Rev. B 52, 1078 (1995).

[2] P. Härtl et al., Phys. Rev. B 105, 174431 (2022).

[3] I. E. Dzyalosinskij, Sov. Phys. JETP 5, 1259 (1957)

[4] T. Moriya, Phys. Rev. 120, 91 (1960).