Electrodeposited magnetic layers in the ultrathin limit
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Introduction The magnetic properties of ultrathin films and nanostructures (moment per atom, anisotropy) are strongly related to the electronic band structure.1 Consequently, very small changes in bond distances and angles or a reduced coordination number such as at surfaces and interfaces may drastically influence the magnetic behavior of nanostructures. A unique way to vary the structural parameters is using epitaxial growth of ultrathin films (a few atomic layers thick) on well-defined single-crystal surfaces with different lattice parameters and orientations.2 Numerous studies have been conducted in ultrahigh vacuum (UHV), combining scanning tunneling microscopy (STM) and other structure-sensitive techniques with in situ magnetic characterizations.3,4 Such investigations have revealed the richness and also the complexity of magnetism at the nanoscale, as one must account not only for structural parameters but also for electronic interactions and charge transfer. Developing the know-how for the preparation of ultrathin films and understanding their magnetic properties allowed the discovery of new effects such as giant magnetoresistance, which is widely used nowadays in hard disk read heads.5 As explained by Switzer and Hodes in the general introduction, metal plating has been known for a long time as a versatile coating technique. Only lately have ultrathin films been considered, essentially soon after the advent of STM and its application in electrochemistry in the early 1990s. In fact,
electrochemical STM was very rapidly established as a central technique to investigate in situ and in real time the structure and reactivity of the electrochemical interface with atomic resolution (for a review, see Reference 6). A second key to progress has been the development of electrochemistry on single crystal electrodes in the 1980s, thanks to the so-called flame annealing technique,7 which allows preparation of well-defined singlecrystal surfaces of noble metals such as gold and platinum group metals under ambient conditions. Early in situ STM studies focused on the initial stages of bulk Cu deposition8 and underpotential deposition (UPD).9 More recent studies focused on the formation of nanostructures10,11 and aimed, for instance, at tailoring the electrocatalytic activity of Pd monolayers by depositing them on different substrates to vary the lattice parameter.12 A few works dealt with magnetic materials in the ultrathin limit (0–2 nm thick).13 In this field, the development of in situ magnetic characterization methods with submonolayer sensitivity has been a major advance in correlating the material structure with its magnetism in the electrolytic environment. The first in situ magnetic characterization was performed at the Institute of Physics of the Federal University in Porto Alegre (Brazil), with enough sensitivity to probe a fraction of one Co atomic layer.14–16 Further progress came with the development of in situ magneto-optical Kerr effect (MOKE) measurements,
P. Allongue, Ecole Polytechnique, Palaiseau, France, phili
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