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Studies of magnetic dipolar interaction between individual atoms using ESR-STM
최태영,Christopher P. Lutz,Andreas Heinrich 한국물리학회 2017 Current Applied Physics Vol.17 No.11
Sensing magnetic interactions at the atomic scale and utilizing those interactions for magnetometry have been highly challenging and important topics in the magnetic resonance community. Recently, electron spin resonance and scanning tunneling microscopy (ESR-STM) have been successfully combined, enabling spin resonance of individual atoms on ultrathin insulating MgO surfaces. When two magnetic atoms are positioned within the separation range of 1 nme4 nm, two spectral features appear in the ESR measurement. The difference in those two frequencies follows a r3 distance-dependence, indicating that the individual atoms are coupled through the magnetic dipolar interaction. Here, we discuss the spin relaxation times that lead to the observed ESR spectra. In addition, we suggest a quantum Hamiltonian model to obtain further insights toward, for example, studies of frustrated spin systems.
Magnetism in Single Metalloorganic Complexes Formed by Atom Manipulation
Choi, T.,Badal, M.,Loth, S.,Yoo, J.-W.,Lutz, C. P.,Heinrich, A. J.,Epstein, A. J.,Stroud, D. G.,Gupta, J. A. American Chemical Society 2014 NANO LETTERS Vol.14 No.3
<P>The magnetic properties of molecular structures can be tailored by chemical synthesis or bottom-up assembly at the atomic scale. We used scanning tunneling microscopy to study charge and spin transfer in individual complexes of transition metals with the charge acceptor, tetracyanoethylene (TCNE). The complexes were formed on a thin insulator, Cu<SUB>2</SUB>N on Cu(100), by manipulation of individual atoms and molecules. The Cu<SUB>2</SUB>N layer decouples the complexes from Cu electron density, enabling direct imaging of the TCNE molecular orbitals as well as spin-flip inelastic electron tunneling spectroscopy. Results were obtained at low temperature down to 1 K and in magnetic fields up to 7 T in order to resolve splitting of spin states in the complexes. We also performed spin-polarized density functional theory calculations to compare with the experimental data. Our results indicate that charge transfer to TCNE leads to a change in spin magnitude, Kondo resonance, and magnetic anisotropy for the metal atoms.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-3/nl404054v/production/images/medium/nl-2013-04054v_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl404054v'>ACS Electronic Supporting Info</A></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>
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>
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
Single atomic spin sensing of magnetic interactions in a tunnel junction
Jinkyung Kim,Won-jun Jang,Thi Hong Bui,Deung-Jang Choi,Christoph Wolf,Fernando Delgado,Yi Chen,Denis Krylov,Soonhyeong Lee,Sangwon Yoon,Christopher P. Lutz,Andreas J. Heinrich,Yujeong Bae 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Single spins are widely regarded as a leading candidate for realizing next-generation quantum devices for sensing and quantum information processing. Detection and coherent control of single spins require to localize single spins and characterize its magnetic surroundings. Scanning tunneling microscopy in combination with electron spin resonance (ESR-STM) technique [1] enables a direct access to the quantum states of single magnetic atoms or molecules on surfaces. Using ESR-STM, we investigated spin resonance of hydrogenated Ti (TiH) atoms adsorbed on bridge binding site of MgO in a two-dimensional vector magnetic field. Here, the spin 1/2 TiH atom with no magnetic anisotropy was employed as a probe of magnetic environments at the tunnel junction. We found both ESR frequency and amplitude change as a function of the angle of vector magnetic fields. The resonance frequency varied by different vector magnetic fields indicates an anisotropy of the g-factor, resulting from the variation of angular momentum contributions due to the crystal fields. We developed a stereoscopic way to unravel the g-factor along the three principal axes. Moreover, ESR amplitude dependence on the direction of magnetic fields provides the further understanding of ESR mechanisms, which results from two factors, tunneling magnetoresistance (TMR) effect at the spin-polarized STM junction and the transverse magnetic field to drive ESR. Our results will enable to predict ESR active spin centers on different substrates as well as in other quantum-nanoscience platforms.
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>