Manuel Steinbrecher

Article

The incorporation of single-molecule magnets into spintronic devices is often hindered by electronic or structural modifications. Here, the authors demonstrate how confinement of Fe 4 molecules in junctions between a Cu 2 N substrate and a scanning microscope tip enhances intra-molecular exchange interaction.

Nature Communications doi: 10.1038/ncomms9216

Authors: Jacob A.J. Burgess, Luigi Malavolti, Valeria Lanzilotto, Matteo Mannini, Shichao Yan, Silviya Ninova, Federico Totti, Steffen Rolf-Pissarczyk, Andrea Cornia, Roberta Sessoli, Sebastian Loth

Author(s): Michael Ruby, Falko Pientka, Yang Peng, Felix von Oppen, Benjamin W. Heinrich, and Katharina J. Franke

We combine scanning-tunneling-spectroscopy experiments probing magnetic impurities on a superconducting surface with a theoretical analysis of the tunneling processes between (superconducting) tip and substrate. We show that the current through impurity-induced Shiba bound states is carried by singl…

[Phys. Rev. Lett. 115, 087001] Published Thu Aug 20, 2015

Nature Physics. doi:10.1038/nphys3418

Authors: Hans T. Nembach, Justin M. Shaw, Mathias Weiler, Emilie Jué & Thomas J. Silva

Proposals for novel spin-orbitronic logic and memory devices are often predicated on assumptions as to how materials with large spin–orbit coupling interact with ferromagnets when in contact. Such interactions give rise to a host of novel phenomena, such as spin–orbit torques, chiral spin structures and chiral spin torques. These chiral properties are related to the antisymmetric exchange, also referred to as the interfacial Dzyaloshinskii–Moriya interaction (DMI; refs , ). For numerous phenomena, the relative strengths of the symmetric Heisenberg exchange and the DMI are of great importance. Here, we use optical spin-wave spectroscopy (Brillouin light scattering) to directly determine the volume-averaged DMI vector D for a series of Ni80Fe20/Pt thin films, and then compare the nearest-neighbour DMI coupling energy with an independently measured value of the Heisenberg exchange for each sample. We show that the dependence on Ni80Fe20 thickness of both the microscopic symmetric and antisymmetric exchange are nearly identical, consistent with the notion that the fundamentals of the DMI and Heisenberg exchange essentially share the same underlying physics, albeit with different symmetries, as was originally proposed by Moriya for superexchange in magnetic oxides, and by Fert and Levy for RKKY coupling in metallic spin glasses. Indeed, our result demonstrates the generality of the original DMI theory, insofar as the proportionality of the symmetric and antisymmetric exchange is robust with regard to the details of spin coupling for the material system in question. Although of significant fundamental importance, this result also leads us to a deeper understanding of DMI and how it could be optimized for spin-orbitronic applications.

Author(s): L. Fanfarillo and E. Bascones

To clarify the nature of correlations in Hund metals and its relationship with Mott physics we analyze the electronic correlations in multiorbital systems as a function of intraorbital interaction U, Hund's coupling JH, and electronic filling n. We show that the main process behind the enhancement o…

[Phys. Rev. B 92, 075136] Published Mon Aug 24, 2015

Author(s): Keiji Doi, Emi Minamitani, Shunji Yamamoto, Ryuichi Arafune, Yasuo Yoshida, Satoshi Watanabe, and Yukio Hasegawa

By utilizing spin-polarized scanning tunneling microscopy (STM) and spectroscopy, we observe the coexistence of perpendicularly and in-plane magnetized cobalt nanoscale islands on an Ag(111) surface. The magnetization direction has the relationship with the observed moiré-corrugation amplitude on th…

[Phys. Rev. B 92, 064421] Published Mon Aug 24, 2015

We combine density functional theory, x-ray magnetic circular dichroism, multiplet calculations, and scanning tunneling spectroscopy to assess the magnetic properties of Fe atoms adsorbed on a thin layer of MgO(100) on Ag(100). Despite the strong axial field due to the O ligand, the weak cubic field induced by the four-fold coordination to Mg atoms entirely quenches the first order orbital moment. This is in marked contrast to Co, which has an out-of-plane orbital moment of $L_z = \pm 3$ that is protected from mixing in a cubic ligand field. The spin-orbit interaction restores a large fraction of the Fe orbital moment leading a zero-field splitting of $14.0 \pm 0.3$~meV, the largest value reported for surface adsorbed Fe atoms.

Low-dimensional quantum magnetism presents a seemingly unlimited source of rich, intriguing physics. Yet, because realistic experimental representations are difficult to come by, the field remains predominantly theoretical. In recent years, artificial spin structures built through manipulation of magnetic atoms in a scanning tunnelling microscope have developed into a promising testing ground for experimental verification of theoretical models. Here, we present an overview of available tools and discuss recent achievements as well as future avenues. Moreover, we show new observations on magnetic switching in a bistable bit that can be used to extrapolate information on the magnetisation of the microscope tip.

Author(s): Qin Liu, Guohua Zhong, Fangfei Ming, Kedong Wang, and Xudong Xiao

Combining scanning tunneling microscopy and first-principles calculations, we have shown that single Co atoms adsorbed on a Si(111)-(7×7) surface have eight different configurations that possess different spin magnetic moments. Despite the large adsorption energy, we have demonstrated that both the ...

[Phys. Rev. B 91, 155417] Published Fri Apr 17, 2015

Author(s): Gábor Mándi and Krisztián Palotás

On the occasion of its 25th anniversary, we revise Chen's derivative rule for electron tunneling [C. J. Chen, Phys. Rev. B 42, 8841 (1990)PRBMDO10.1103/PhysRevB.42.8841] for the purpose of computationally efficient simulations of scanning tunneling microscopy (STM) based on first-principles electron...

[Phys. Rev. B 91, 165406] Published Thu Apr 09, 2015

The printed organs coming to a body near you

Nature 520, 7547 (2015). http://www.nature.com/doifinder/10.1038/520273a

Author: Heidi Ledford

From kidneys to hands, 3D printers can now churn out made-to-order organs and bones using cells as ‘ink’.

Author(s): Matthias Emmrich, Maximilian Schneiderbauer, Ferdinand Huber, Alfred J. Weymouth, Norio Okabayashi, and Franz J. Giessibl

We study the physics of atomic manipulation of CO on a Cu(111) surface by combined scanning tunneling microscopy and atomic force microscopy at liquid helium temperatures. In atomic manipulation, an adsorbed atom or molecule is arranged on the surface using the interaction of the adsorbate with subs...

[Phys. Rev. Lett. 114, 146101] Published Mon Apr 06, 2015

Author(s): Yan Liu, Haifeng Du, Min Jia, and An Du

We study the spin-transfer-induced dynamics of a target skyrmion in the free layer of nanopillar structures, in which the polarizer layer has a perpendicular magnetization. By using micromagnetic simulations, it is shown that three distinct modes can be excited. As a consequence of the evolution of ...

[Phys. Rev. B 91, 094425] Published Tue Mar 24, 2015

Author(s): Q. Dubout, F. Donati, C. Wäckerlin, F. Calleja, M. Etzkorn, A. Lehnert, L. Claude, P. Gambardella, and H. Brune

Cobalt atoms exposed to hydrogen gas have higher spins, an effect that could be used to build magnetic nanostructures and lattices.

[Phys. Rev. Lett. 114, 106807] Published Wed Mar 11, 2015

Author(s): Liwei Liu, Kai Yang, Yuhang Jiang, Boqun Song, Wende Xiao, Shiru Song, Shixuan Du, Min Ouyang, Werner A. Hofer, Antonio H. Castro Neto, and Hong-Jun Gao

The magnetic structure of a magnetic metal-organic complex on a gold surface can be mapped by exploring the field dependence of the extended Kondo effect.

[Phys. Rev. Lett. 114, 126601] Published Tue Mar 24, 2015

Nature Nanotechnology 10, 187 (2015). doi:10.1038/nnano.2015.24

Authors: Andrew D. Kent & Daniel C. Worledge

Solid-state memory devices with all-electrical read and write operations might lead to faster, cheaper information storage.

Nature Nanotechnology 10, 195 (2015). doi:10.1038/nnano.2015.41

Authors: Stuart Parkin & See-Hun Yang

Racetrack memory stores digital data in the magnetic domain walls of nanowires. This technology promises to yield information storage devices with high reliability, performance and capacity.

Author(s): Rasmus Westerström, Anne-Christine Uldry, Roland Stania, Jan Dreiser, Cinthia Piamonteze, Matthias Muntwiler, Fumihiko Matsui, Stefano Rusponi, Harald Brune, Shangfeng Yang, Alexey Popov, Bernd Büchner, Bernard Delley, and Thomas Greber

The interaction between the endohedral unit in the single-molecule magnet Dy₂ScN@C₈₀ and a rhodium (111) substrate leads to alignment of the Dy 4f orbitals. The resulting orientation of the Dy₂ScN plane parallel to the surface is inferred from comparison of the angular anisotropy of x-ray absorption...

[Phys. Rev. Lett. 114, 087201] Published Mon Feb 23, 2015

Author(s): Kirsten von Bergmann, Markus Ternes, Sebastian Loth, Christopher P. Lutz, and Andreas J. Heinrich

Spin-resolved scanning tunneling microscopy is employed to quantitatively determine the spin polarization of the magnetic field-split Kondo state. Tunneling conductance spectra of a Kondo-screened magnetic atom are evaluated within a simple model taking into account inelastic tunneling due to spin e...

[Phys. Rev. Lett. 114, 076601] Published Fri Feb 20, 2015

Nature journals offer double-blind review

Nature 518, 7539 (2015). doi:10.1038/518274b

Starting in March, Nature and the monthly Nature research journals will offer an alternative to conventional peer review. Authors will be able to request that their names and affiliations are withheld from reviewers of their papers — a form of peer review known as

Author(s): Jan Müller and Achim Rosch

Magnetic whirls in chiral magnets, so-called skyrmions, can be manipulated by ultrasmall current densities. Here we study both analytically and numerically the interactions of a single skyrmion in two dimensions with a small hole in the magnetic layer. Results from micromagnetic simulations are in g...

[Phys. Rev. B 91, 054410] Published Tue Feb 17, 2015

Author(s): Andrew Allerdt, C. A. Büsser, G. B. Martins, and A. E. Feiguin

Magnetic impurities embedded in a metal interact via an effective Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mediated by the conduction electrons, which is commonly assumed to be long ranged, with an algebraic decay in the interimpurity distance. However, they can also form a Kondo screened state...

[Phys. Rev. B 91, 085101] Published Mon Feb 02, 2015

Author(s): G. Hasselberg, R. Yanes, D. Hinzke, P. Sessi, M. Bode, L. Szunyogh, and U. Nowak

We report a detailed study of the magnetic properties of a monoatomic layer of Mn on W(110). By comparing multiscale numerical calculations with measurements we evaluate the magnetic ground state of the system and its temperature-dependent evolution. We find that the ground state consists of a cyclo...

[Phys. Rev. B 91, 064402] Published Mon Feb 02, 2015

Author(s): Michael Schackert, Tobias Märkl, Jasmin Jandke, Martin Hölzer, Sergey Ostanin, Eberhard K. U. Gross, Arthur Ernst, and Wulf Wulfhekel

Inelastic tunneling spectroscopy of Pb islands on Cu(111) obtained by scanning tunneling microscopy below 1 K provides a direct access to the local Eliashberg function of the islands with high energy resolution. The Eliashberg function describes the electron-phonon interaction causing conventional s...

[Phys. Rev. Lett. 114, 047002] Published Thu Jan 29, 2015

Atomic-scale magnetic nanostructures are promising candidates for future information processing devices. Utilizing external electric field to manipulate their magnetic properties is an especially thrilling project. Here, by carefully identifying the different contributions of each atomic orbital to the magnetic anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is possible to engineer both the MAE and the magnetic response to the electric field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a matrix, we propose several interesting iron nanostructures with dramatically different magnetic properties. Such nanostructures could exhibit a strong magnetoelectric effect. Our work may open new avenues to the artificial design of electrically controlled magnetic devices.

Michelson–Morley analogue for electrons using trapped ions to test Lorentz symmetry

Nature 517, 7536 (2015). doi:10.1038/nature14091

Authors: T. Pruttivarasin, M. Ramm, S. G. Porsev, I. I. Tupitsyn, M. S. Safronova, M. A. Hohensee & H. Häffner

All evidence so far suggests that the absolute spatial orientation of an experiment never affects its outcome. This is reflected in the standard model of particle physics by requiring all particles and fields to be invariant under Lorentz transformations. The best-known tests of this important cornerstone of physics are Michelson–Morley-type experiments verifying the isotropy of the speed of light. For matter, Hughes–Drever-type experiments test whether the kinetic energy of particles is independent of the direction of their velocity, that is, whether their dispersion relations are isotropic. To provide more guidance for physics beyond the standard model, refined experimental verifications of Lorentz symmetry are desirable. Here we search for violation of Lorentz symmetry for electrons by performing an electronic analogue of a Michelson–Morley experiment. We split an electron wave packet bound inside a calcium ion into two parts with different orientations and recombine them after a time evolution of 95 milliseconds. As the Earth rotates, the absolute spatial orientation of the two parts of the wave packet changes, and anisotropies in the electron dispersion will modify the phase of the interference signal. To remove noise, we prepare a pair of calcium ions in a superposition of two decoherence-free states, thereby rejecting magnetic field fluctuations common to both ions. After a 23-hour measurement, we find a limit of h × 11 millihertz (h is Planck’s constant) on the energy variations, verifying the isotropy of the electron’s dispersion relation at the level of one part in 1018, a 100-fold improvement on previous work. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming that Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold-improved limit on anisotropies in the speed of light. Our result probes Lorentz symmetry violation at levels comparable to the ratio between the electroweak and Planck energy scales. Our experiment demonstrates the potential of quantum information techniques in the search for physics beyond the standard model.

Author(s): Kai Di, Vanessa Li Zhang, Hock Siah Lim, Ser Choon Ng, Meng Hau Kuok, Jiawei Yu, Jungbum Yoon, Xuepeng Qiu, and Hyunsoo Yang

The interfacial Dzyaloshinskii-Moriya interaction in an in-plane anisotropic Pt(4  nm)/Co(1.6  nm)/ Ni(1.6  nm) film has been directly observed by Brillouin spectroscopy. It is manifested as the asymmetry of the measured magnon dispersion relation, from which the Dzyaloshinskii-Moriya interaction co...

[Phys. Rev. Lett. 114, 047201] Published Wed Jan 28, 2015