Suchergebnisse

We show that the magnetic ordering of coupled atomic dimers on a superconductor is revealed by their intragap spectral features. Chromium atoms on the superconductor β−Bi2Pd surface display Yu-Shiba-Rusinov bound states, detected as pairs of intragap excitations in tunneling spectra. By means of atomic manipulation with a scanning tunneling microscope's tip, we form Cr dimers with different arrangements and find that their intragap features appear either shifted or split with respect to single atoms. These spectral variations are associated with the magnetic coupling, ferromagnetic or antiferromagnetic, of the dimer, as confirmed by density functional theory simulations. The striking qualitative differences between the observed tunneling spectra prove that intragap Shiba states are extremely sensitive to the magnetic ordering on the atomic scale. ; D.-J. C. and J. I. P. thank the European Union for support under the H2020-MSCA-IF2014 Marie-Curie Individual Fellowship program (Proposal No. 654469), Spanish MINECO (MAT2016-78293-C6-1-R), Diputacion Foral de Gipuzkoa for Grant No. 64/15, and the European Regional Development Fund (ERDF). N. L. thanks Spanish MINECO (Grant No. MAT2015-66888-C3-2-R). M. M. U. acknowledges Spanish MINECO (MAT2014-60996-R). E. H., I. G., and H. S. acknowledge FIS2014-54498-R and MDM-2014-0377, COST MP16218 nanocohybri, ERC PNICTEYES Grant Agreement No. 679080, and Departamento Administrativo de Ciencia, Tecnología e Innovación, COLCIENCIAS (Colombia), Programa doctorados en el exterior and convocatoria 568-2012, as well as Comunidad de Madrid through program NanofrontmagCM (Grant No. S2013/MIT-2850). ; Peer reviewed

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy. ; We acknowledge funding from the European Research Council under the European Union's Horizon 2020 programme (Grant Agreement No. 635919), and from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6, MAT2015-66888-C3-2-R), Agencia Estatal de Investigación (AEI)/FEDER, UE (CTQ2016-75960-P), the AGAUR (2017 SGR 1257), and the CERCA Program/Generalitat de Catalunya. ; Peer reviewed

Nanometer-thick epitaxial Co films intercalated between graphene (Gr) and a heavy metal (HM) substrate are promising systems for the development of spin–orbitronic devices due to their large perpendicular magnetic anisotropy (PMA). A combination of theoretical modeling and experiments reveals the origin of the PMA and explains its behavior as a function of the Co thickness. High quality epitaxial Gr/Con/HM(111) (HM = Pt,Ir) heterostructures are grown by intercalation below graphene, which acts as a surfactant that kinetically stabilizes the pseudomorphic growth of highly perfect Co face-centered tetragonal (fct) films, with a reduced number of stacking faults as the only structural defect observable by high-resolution scanning transmission electron microscopy (STEM). Magneto-optic Kerr effect (MOKE) measurements show that such heterostructures present PMA up to large Co critical thicknesses of about 4 nm (20 ML) and 2 nm (10 ML) for Pt and Ir substrates, respectively. X-ray magnetic circular dichroism (XMCD) measurements show an inverse power law of the anisotropy of the orbital moment with Co thickness, reflecting its interfacial nature, that changes sign at about the same critical values. First principles calculations show that, regardless of the presence of graphene, ideal Co fct films on HM buffers do not sustain PMAs beyond around 6 mLs due to the in-plane contribution of the inner bulk-like Co layers. The large experimental critical thicknesses sustaining PMA can only be retrieved by the inclusion of structural defects that promote a local hcp stacking such as twin boundaries or stacking faults. Remarkably, a layer resolved analysis of the orbital momentum anisotropy reproduces its interfacial nature, and reveals that the Gr/Co interface contribution is comparable to that of the Co/Pt(Ir). ; Financial support from MINECO (Grant Nos. RTI2018-097895-B-C41, RTI2018-097895-B-C42 and RTI2018-097895-B-C43 (FUN-SOC), PID2019-103910GB-I00, FIS2016-78591-C3-1-R and FIS2016-78591-C3-2-R (SKYTRON), PGC2018-098613-B-C21 (SpOrQuMat), PCI2019-111908-2 and PCI2019-111867-2 (FLAGERA 3 grant SOgraphMEM)], from Regional Government of Madrid (grant number P2018/NMT-4321 (NANOMAGCOST-CM)) and from Gobierno Vasco-UPV/EHU (grant numbers GIU18/138 and IT-1246-19). We acknowledge experiments at ALBA BL29 via proposal no. 2019023333. IMDEA-Nanociencia acknowledges support from the "Severo Ochoa" Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). ; Peer reviewed