Surface structure determination of Pd ultrathin films on Ru(0001): Possible magnetic behavior

Abstract

Nowadays, ultrathin films play a fundamental role in modern materials science and technology. Recently, several theoretical works indicate that the magnetic properties of Pd ultrathin films could be controlled by structural parameters of the film, and much work has been done to study induced magnetic properties of ultrathin Pd films grown on different substrates. For the epitaxy of Pd monolayers on Ru͑0001͒, it was not clear if Pd grows in an hcp or fcc structure and a detailed surface structure determination was not available for this system. In this study, Pd films with thicknesses ranging from submonolayer up to approximately 15 ML were grown on a Ru͑0001͒ single crystal substrate under UHV conditions, and the electronic structure, surface crystallography, and magnetism were investigated by multiple ͑experimental and theoretical͒ techniques: x-ray photoelectron spectroscopy and diffraction using conventional Mg K␣ and synchrotron radiation sources, lowand high-energy electron diffraction, magneto-optical Kerr effect measurements, and density-functional theory calculations. The electronic structure, surface crystallography, and magnetism of the Pd films are discussed in detail.

Evidencing the formation of Pt nano-islands on Cr2O3/Ag(111)

“…In the relaxation using Pt atoms as the emitter, T θ ≈ 170.0 K, very close to the expected value for the surface component (T θsurface ≈ 1/√2 T θbulk reported for Pt). 51 For chromium atoms as the emitter, T θ = 630 K was obtained, precisely the value reported for the Cr bulk (T θ = 630 K). 52 The model structures considering different Cr 2 O 3 surface terminations were also proposed.…”

Atomic Structure of Cr2O3/Ag(111) and Pd/Cr2O3/Ag(111) Surfaces: A Photoelectron Diffraction Investigation

“…In particular, at 300 K, three-dimensional Pd islands with a very low aspect ratio were formed . Particularly, the lateral Pd–Pd distance expansion could play an important role in inducing a magnetic ordering in Pd atoms, as predicted theoretically. − A possible way to induce ferromagnetism in Pd is by modifying the atomic arrangement of nonmagnetic atoms . The existence of ferromagnetism in Pd films with fcc structure, with an expansion of between 10 and 32% in the lattice parameter, where it would reach the value of 0.36 μ B , has been predicted.…”

“…An unconventional hcp Pd film with the lateral lattice parameter expanded is also predicted by DFT calculations to hold spontaneous ferromagnetic ordering. 37 Therefore, different packing possibilities and crystalline structures (fcc and hcp) for the [111] direction were tested, where the bulk lattice parameter (a = 3.89 Å), interlayer distance (2.25 Å), and lateral distance between Pd atoms (2.75 Å) were fixed. Figure 10b shows the Pd film with the fcc structure, ABCA packing, and bulk distances proposed for the simulations.…”

“…34−36 A possible way to induce ferromagnetism in Pd is by modifying the atomic arrangement of nonmagnetic atoms. 37 The existence of ferromagnetism in Pd films with fcc structure, with an expansion of between 10 and 32% in the lattice parameter, 36 where it would reach the value of 0.36 μ B , has been predicted.…”

A new ultra-high-vacuum variable temperature and high-magnetic-field X-ray magnetic circular dichroism facility at LNLS

“…From an experimental point of view, to demonstrate and understand the physical mechanism involved in such systems certainly would contribute to the understanding of nanomagnetism, and might be important for future break-throughs in the area. Nevertheless, the topic is still controversial and an open question, since, to the best of our knowledge, there is not an incontestable published experimental result demonstrating that the origin of the ferromagnetic signal derives from the Pd atoms in pure Pd particles, nanowires or ultrathin films and not from contaminants, or is induced by other magnetic materials or even from experimental artifacts (de Siervo et al, 2007;Hü ger & Osuch, 2005;Taniyama et al, 1997;Abraham et al, 2005). Therefore, it is essential to identify carefully the contributions to the ferromagnetic signal using an element-specific technique.…”