GD-03 Magnetic domain structures of rare-earth metal surfaces

Rare earth metals (REMs) are difficult, if not impossible, to clean as bulk materials due to their extreme reactivity. Therefore, films of REMs are studied to explore their rich magnetic properties, which are primarily influenced by the element-specific sign and wavelength of the RKKY interaction. Based on their complex cleaning procedure, the magnetic behavior of REM(0001) surfaces remains a subject of ongoing debate [1,2], while it is still unknown for most of them. Here we present investigations of complex magnetic structures on epitaxial REM films grown on W(110) using spin-polarized scanning tunneling microscopy (SP-STM). In a recent study of the thickness-dependent domain structures of Gd(0001) films, we confirmed a spin reorientation transition [3], where the easy magnetization axis changes from in-plane to out-of-plane at a critical thickness Θcrit ≈ (100±20) atomic layers (AL) [1]. Below Θcrit, we observed µm-sized in-plane domains aligned along the [1-10] direction of W(110). Above Θcrit, out-of-plane magnetized zig-zag-shaped stripe domains become dominant. The magnetic domain structure of Tb(0001) films produces a sixfold magnetic contrast, consistent with the expected in-plane orientation of magnetic domains, similar to earlier findings in Dy(0001)/W(110) [4]. We find that the density of structural defects and dislocations decreases with increasing Tb film thickness, leading to the formation of larger domains. Analysis of the domain walls reveals their Néel character, with widths of approximately 1.4 nm, 2.5 nm, and 3.0 nm for 60°, 120°, and 180° domain walls, respectively.References: [1] P. Härtl et al., Phys. Rev. B 105, 174431 (2022). [2] P. Härtl et al., Phys. Rev. B, submitted July 2024. [3] A. Berger et al., Phys. Rev. B 52, 1078 (1995). [4] L. Berbil-Bautista et al., Phys. Rev. B 76, 064411 (2007). [5] J. E. Prieto, et al., Phys. Rev. B 94, 174445 (2016).