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Hyperfine interaction of individual atoms on a surface
Willke, Philip,Bae, Yujeong,Yang, Kai,Lado, Jose L.,Ferró,n, Alejandro,Choi, Taeyoung,Ardavan, Arzhang,Ferná,ndez-Rossier, Joaquí,n,Heinrich, Andreas J.,Lutz, Christopher P. American Association for the Advancement of Scienc 2018 Science Vol.362 No.6412
<P>Taking advantage of nuclear spins for electronic structure analysis, magnetic resonance imaging, and quantum devices hinges on knowledge and control of the surrounding atomic-scale environment. We measured and manipulated the hyperfine interaction of individual iron and titanium atoms placed on a magnesium oxide surface by using spin-polarized scanning tunneling microscopy in combination with single-atom electron spin resonance. Using atom manipulation to move single atoms, we found that the hyperfine interaction strongly depended on the binding configuration of the atom. We could extract atom-and position-dependent information about the electronic ground state, the state mixing with neighboring atoms, and properties of the nuclear spin. Thus, the hyperfine spectrum becomes a powerful probe of the chemical environment of individual atoms and nanostructures.</P>
Electrically controlled nuclear polarization of individual atoms
Yang, Kai,Willke, Philip,Bae, Yujeong,Ferró,n, Alejandro,Lado, Jose L.,Ardavan, Arzhang,Ferná,ndez-Rossier, Joaquí,n,Heinrich, Andreas J.,Lutz, Christopher P. Nature Publishing Group 2018 Nature nanotechnology Vol.13 No.12
Reading and writing single-atom magnets
Natterer, Fabian D.,Yang, Kai,Paul, William,Willke, Philip,Choi, Taeyoung,Greber, Thomas,Heinrich, Andreas J.,Lutz, Christopher P. Macmillan Publishers Limited, part of Springer Nat 2017 Nature Vol.543 No.7644
<P>The single-atom bit represents the ultimate limit of the classical approach to high-density magnetic storage media. So far, the smallest individually addressable bistable magnetic bits have consisted of 3-12 atoms(1-3). Long magnetic relaxation times have been demonstrated for single lanthanide atoms in molecular magnets(4-12), for lanthanides diluted in bulk crystals(13), and recently for ensembles of holmium (Ho) atoms supported on magnesium oxide (MgO)(14). These experiments suggest a path towards data storage at the atomic limit, but the way in which individual magnetic centres are accessed remains unclear. Here we demonstrate the reading and writing of the magnetism of individual Ho atoms on MgO, and show that they independently retain their magnetic information over many hours. We read the Ho states using tunnel magnetoresistance(15,16) and write the states with current pulses using a scanning tunnelling microscope. The magnetic origin of the long-lived states is confirmed by single-atom electron spin resonance(17) on a nearby iron sensor atom, which also shows that Ho has a large out-of-plane moment of 10.1 +/- 0.1 Bohr magnetons on this surface. To demonstrate independent reading and writing, we built an atomic-scale structure with two Ho bits, to which we write the four possible states and which we read out both magnetoresistively and remotely by electron spin resonance. The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is indeed possible.</P>
Atomic-scale sensing of the magnetic dipolar field from single atoms
Choi, Taeyoung,Paul, William,Rolf-Pissarczyk, Steffen,Macdonald, Andrew J.,Natterer, Fabian D.,Yang, Kai,Willke, Philip,Lutz, Christopher P.,Heinrich, Andreas J. Nature Publishing Group, a division of Macmillan P 2017 Nature nanotechnology Vol.12 No.5
<P>Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions(1). In recent years, there have been notable achievements in detecting(2) and coherently controlling(3-7) individual atomic-scale spin centres for sensitive local magnetometry(8-10). However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges(11,12). Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r(-3.01+/-0.04)). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.</P>