There exist only 4 elements which are ferromagnetic at room temperature: iron, cobalt, nickel, and the —far less well-known— rare-earth metal gadolinium (Gd). Although rare-earth metals are highly important in countless applications, for example in wind-powered electrical generators, their magnetic domain structure is largely unknown. The term "magnetic domain structure" describes, loosely speaking, the distribution and shape of magnetic "north and south poles".
In a recent study, Patrick Härtl and Dr. Markus Leisegang investigated the domain structure of Gd films by means of spin-polarized scanning tunneling microscopy (SP-STM). This technique allows the imaging of magnetic domains with a spatial resolution down to the scale of single atoms. When depositing highly pure Gd films on a single-crystalline tungsten substrate, they noticed that the growth conditions, such as the substrate temperature, singnificantly impact the magnetic properties. Only for optimally prepared, very smooth films well-defined domain structures could be observed. As shown in the image above, these films were found to exhibit a spin-reorientation transition, i.e., the film is magnetized within the film plane at low film thickness (left panel) but perpendicular to the film plane at higher film thickness (right). The results have been published in Phys. Rev. B 105, 174431 (2022).