Magnetic Domain Structures on Gd(0001)/W(110) Films

Due to their partially filled 4f shell which are coupled by the RKKY interaction, rare earth metals exhibit long-range magnetic order. Depending on the sign of the RKKY coupling and details of the sample geometry many different domain structures have been observed. For example, spin-resolved STM studies of Dy(0001) thin films on W(110) revealed a six-fold symmetric magnetic domain structure [1]. Here we report on similar experiments on Gadolinium (Gd) films epitaxially grown on W(110). Gd is a ferromagnetic metal with a Curie temperature of 293 K.  Its half-filled 4f shell results in an almost spherical charge distribution and therefore a rather small magnetic anisotropy in comparison other rare earth metals [2].

Earlier spatially averaging experiments [2] suggest that Gd(0001) films on W(110) exhibit a thickness-dependent spin reorientation transition at around 40 nm from in-plane at thin films to out-of-plane for thicker. Our investigation on Gd(0001) films grown on W(110) indeed show a rather rich spin structure in STM/STS studies. For rather thin film thicknesses we observe large in-plane domains (several µm large) oriented along the [1-10] direction of the W(110) substrate. Above approximately 100 atomic layers, a significant contribution of the out-of-plane magnetization emerges. This leads to spin spiral-like magnetic domains with in-plane as well as out-of-plane components. The periodicity of these zig-zag stripe domains increases with increasing film thickness from (50 ± 10) nm up to (120 ± 40) nm. We will discuss the transition of the magnetic structure in dependence of the Gd film thickness.

[1] Berbil-Bautista et. al., Phys. Rev. B 76, 064411 (2007)

[2] Berger et. al., PhysRevB.52.1078 (1995)