Harald Brune

Harald Brune

Affiliation: Ecole Polytechnique Federale de Lausanne

Research Interests: Catalysis of Nanostructures

Title: News from Rare Earth Atoms on Surfaces

Abstract: The magnetic stability of the best single atom magnets is reaching temperatures approaching their on set temperature of diffusion. One example is Ho on the O site ofMgO(100) films, exhibiting magnetic bista-bility up to45 K [1]. However, diffusion from the O to the bridge site, where Ho becomes paramagnetic, sets inclose to that temperate, namely, between 58 and 70K[2]. A second case is Dy, again on the O site of the same substrate. It has a 40% higher anisotropy barrier and istherefore expected to exhibit magnetic bistability well above 45K, yet thermal diffusion to the bridge site may set in at lower temperatures [2,3].Evidently, this limits further progress towards stable magnetization in single atoms at higher temperatures.We present with Dy/NaCl films a new system where the atoms are on substitutional adsorption sites and stable against diffusion up to 300K. Despite the lateral coordination in these sites, hitherto thought to be detrimental to magnetic stability, the atoms exhibit magnetic hysteresis at lowT[4].In addition to the sub-stitutional species one can create samples with ad atoms that exhibit longer magnetic relaxation times but evidently, as the other single atom magnet systems, these ad atoms start to diffuse at lowT. NaCl was so far not used as a decoupling layer for single atom magnets. The fact that it works, implies low phonon density of states at the energies relevant for magnetic relaxation and an efficient decoupling from the electrons of the underlying metal substrate [4].Tb atoms onO sites ofMgO(100) thin films are single atom magnets with surprising magnetic relaxation[5].Namely, their magnetic relaxation time depends on the magnetic field applied before removing it to study the relaxation. We find that this effect only appears in the presence of secondary electrons that are created by XMCD measurements. Looking at this system with STM confirms the magnetic level scheme derived from DFT and XAS and shows no sign of spontaneous magnetic relaxation up to 30K [6].