Co Nanodot Arrays Grown on a GdAu₂ Template: Substrate/Nanodot Antiferromagnetic Coupling

Abstract

Controlling anisotropy and exchange coupling in patterned magnetic nanostructures is the key for developing advanced magnetic storage and spintronic devices. We report on the antiferromagnetic interaction between a Co nanodot array and its supporting GdAu2 nanotemplate that induces large anisotropy values in individual Co nanodots. In clear contrast with nonmagnetic Au substrates, GdAu2 triggers an earlier switch from out-of-plane anisotropy in monatomic high dots to in-plane when the dot height becomes biatomic.

Growth of Co Nanomagnet Arrays with Enhanced Magnetic Anisotropy

“…A similar AFM coupling was already observed for Co nanodots grown on GdAu 2 layers,18 although in the present case, however, the absence of magnetic saturation in the Gd hysteresis loops points to a very strong AFM coupling (see Figure 3d). Note the difference with the continuous GdAu 2 substrate, where magnetic ordering in the Gd substrate lattice exists prior to Co evaporation 18. In the trigon network, in contrast, Gd atoms only become magnetically arranged by interacting with magnetic Co.…”

“…However, a fit with two functions (not shown) deviates strongly from the experimental results. Therefore, we conclude that all Gd atoms in the trigon phase, embedded in DLs or within triangular nodes, act as single paramagnetic impurities, in contrast with the ferromagnetic order found in the GdAu 2 monolayer 18, 19. In the present case, the absence of ferromagnetism in the crystalline trigon nodes is likely due to their reduced lateral size 29…”

“…Another possibility to create templates is profiting the lattice mismatch between a substrate and a monolayer‐thick film of a different material that can give rise to the formation of Moiré patterns which in many occasions are found to work as chemically and structurally stable templates for the growth of nanostructures. This has been observed for graphene,12 BN based structures,13, 14 as well as in rare‐earth/Au or Ag monolayer‐thick alloys 15, 16, 17, 18, 19, 20. Certainly, a further possibility is the use of strain‐relief dislocation networks as modulated substrates, as shown, e.g., in the case of Ag and Cu monolayers on Pt(111) 21…”

“…Moreover, an additional difference to the Co/Au system is the presence of 1 AL high nanodots on trigon networks. Monolayer‐thick nanodots were not observed on Co on Au(111),6, 30 although they form on GdAu 2 18…”

Magnetism and morphology of Co nanocluster superlattices onGdAu2/Au(111)–(13×13)

“…At larger fields the Gd signal is dominated by the paramagnetic contribution of Gd atoms which are not exchange-coupled to the Co clusters. The comparison between thick clusters and an in-plane easy axis for thicker ones [28], support a mixed configuration with cluster height-dependent easy axes.…”