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).