Chiral magnetic interaction between two individual atoms

Tailoring the chiral magnetic interaction between two individual atoms
A. A. Khajetoorians, M. Steinbrecher, M. Ternes, M. Bouhassoune, M. dos Santos Dias, S. Lounis, J. Wiebe & R. Wiesendanger
Nature Communications 7, 10620 (2016)

The interaction between two magnetic atoms (red/green) is mediated by scattering of conduction electrons at a substrate atom (grey) with strong spin-orbit coupling (SOC)2,15,16. The shown scattering process leads to a contribution to the Heisenberg-like exchange (J) and DM vector (D), which is oriented perpendicular to the indicated triangle constituted by the two magnetic atoms and the substrate atom. The overall J and D are given by the contributions of all substrate atoms resulting in a nonzero D=(D||, D⊥, Dz) (orientation of the components as indicated) because of broken inversion symmetry at the surface18. The orientation of the spins S1 and S2 of the coupled pair is determined by the interplay between the single ion magnetic anisotropy of each atom (Ki), J, D, and the applied magnetic field (Bz).

Dipolar helices

Structure and cohesive energy of dipolar helices.
Igor Stankovic,Miljan Dasic and René Messina
Soft Matter 12, 3056 (2016)

This paper deals with the investigation of cohesive energy in dipolar helices made up of hard spheres. Such tubular helical structures are ubiquitous objects in biological systems. We observe a complex dependence of cohesive energy on surface packing fraction and dipole moment distribution. As far as single helices are concerned, the lowest cohesive energy is achieved at the highest surface packing fraction.

Infinite geometric frustration in a cubic dipole cluster

Infinite geometric frustration in a cubic dipole cluster.

Johannes Schönke, Tobias M. Schneider, and Ingo Rehberg

Phys. Rev. B 91, 020410(R) (2015)

(a) Rendering of eight dipoles as arrows located at the corners of a cube. The colored and translucent arrows show selected orientations in the ground state of the system which is a continuum of infinitely many configurations. The continuum corresponds to rotations of the dipoles in planes perpendicular to the cube's volume diagonal of the respective corner in analogy to the mechanical system in Fig. 2. Pairs of dipoles in opposing corners are always parallel. (b) Magnetic energy landscape for eight dipoles located at the corners of a cube. The energy is shown as a function of the two orientation angles of one dipole, covering all possible orientations. The other seven dipoles adjust to the respective minimum energy configuration. The white line through the “valley” marks the continuous ground state. (c) Rendering of eight bevel gears located at the corners of a cube. The rotation axes point to the cube's center and every gear interlocks with its three edge neighbors. The motion of this mechanical system, indicated by the red arrows, corresponds to the motion of the ground state continuum in the magnetic system.

Smooth Teeth: Why Multipoles Are Perfect Gears

Smooth Teeth: Why Multipoles Are Perfect Gears.
Johannes Schönke
Phys. Rev. Applied 4, 064007 (2015)

Definition of the angles which describe the rotation of the dipoles (red). The upper panel introduces the two angles θ and φ which set the positions of the rotation axes (light gray). The rotation axes are restricted to lie in the x−y plane. The angles θ and φ (and, therefore, the rotations axes) are fixed for a given configuration. The lower panel introduces the angles α and β which correspond to the 2 degrees of freedom the system possesses. α and β describe the actual orientation of the two dipoles during rotation.

Thernal Stability of Circular Nanomagnets

Thermal Stability of Magnetic States in Circular Thin-Film Nanomagnets with Large Perpendicular Magnetic Anisotropy.

Gabriel D. Chaves-O’Flynn, Georg Wolf, Jonathan Z. Sun, and Andrew D. Kent

Phys. Rev. Applied 4, 024010 (2015)

Energy barriers normalized to U0 calculated by the domain-wall model Eq. (14) (dashed lines) and obtained with the string method (solid points) for different applied fields and disk diameters. The black solid line corresponds to the macrospin model without applied field.

Opportunities at the Frontiers of Spintronics

Opportunities at the Frontiers of Spintronics.

Axel Hoffmann and Sam D. Bader

Phys. Rev. Applied 4, 047001 (2015)

Schematics of (a) a vortexlike (Bloch) and (b) a hedgehoglike (Néel) magnetic skyrmion structure. The vortexlike skyrmions are typical for skyrmions generated by bulk (c) chiral Dzyaloshinskii-Moriya interactions, such as in B20 compounds, while the hedgehoglike skyrmions are generally stabilized from interfacial (d) chiral Dzyaloshinskii-Moriya interactions.

Ultrafast dynamics in FePt

Modeling of Ultrafast Heat- and Field-Assisted Magnetization Dynamics in FePt

P. Nieves and O. Chubykalo-Fesenko

Phys. Rev. Applied 5, 014006 (2016)

Snapshots of the system magnetization state in the continuous film with F=40  mJ/cm3 and μ0Hz=−3  T at time moments (a) t=0.25  ns, (b) t=0.5  ns, (c) t=3.2  ns, and (d) t=3.6  ns. The figures show an area of 150×150  nm.

How to Store Energy in Dirac Strings

Dynamics of Bound Monopoles in Artificial Spin Ice: How to Store Energy in Dirac Strings.

E. Y. Vedmedenko

Phys. Rev. Lett. 116, 077202 (2016)

(a, b) Examples of microscopic configurations used for static calculations. Color scheme gives the energy per dipole. (c) Total energy cost due to formation of DSs of length r in a sample 200a×200a. Numerical data (dots) are fitted by Eq. (1) with T0≈7.3w/a and γ≈0.5wa. The inset gives the difference between the total potential and the linear term T0r. (d) Spatial energy profile along the DSs of panel (a) and schematic drawing of T1 and T2 vertices. (e) Interaction potential between two BMs of opposite sign in different backgrounds calculated analytically (dots). Lines are fits by function γ/r with γ≈1/2. The γ/r term is repulsive.

 

Colloidal crystals assemblies and applications: Review

Designed Assembly and Integration of Colloidal Nanocrystals for Device Applications.

Jiwoong Yang, Moon Kee Choi, Dae-Hyeong Kim and Taeghwan Hyeon

Advanced Materials 28,1176 (2016)

The preparation, formatting, and applications of colloidal nanoparticle solids have burgeoned tremendously over the last thirty years due to the remarkable crossover of ideas from many materials science fields. Here, general information on the preparation of colloidal nanocrystalline solids via thin-film formation and various printing techniques is presented. In addition, their integration into a number of advanced electronic applications is discussed.

Effects of the individual particle relaxation time on superspin glass dynamics

Effects of the individual particle relaxation time on superspin glass dynamics.

Mikael Svante Andersson, Jose Angel De Toro, Su Seong Lee, Peter S. Normile, Per Nordblad, and Roland Mathieu

Phys. Rev. B 93, 054407 (2016)

MIRM vs temperature using a perturbation field of 40 A/m and th=300 s for several halting temperatures; Th=50, 60, 70, 80, 90, 100, and 110 K for (a) RCP6 and (b) RCP8. (c) Selected MIRM(T) curves for RCP6 and RCP8 plotted together. Data for RCP8 is adapted from Ref. [15].

High-frequency magnetization dynamics of individual atomic-scale magnets

High-frequency magnetization dynamics of individual atomic-scale magnets.

S. Krause, A. Sonntag, J. Hermenau, J. Friedlein, and R. Wiesendanger

Phys. Rev. B 93, 064407 (2016)

(a) Telegraphic noise z(t) on a nanomagnet at low and high I at closed feedback loop, and respective data histograms. (U=100 mV, T=45 K) (b) Top: Periodic sequence of high and low tunnel bias. Bottom: Resulting noise I on a thermally switching nanomagnet at constant tip-sample distance. (c) Averaged noise signal during one cycle, calculated from I(t) in (b).

Self-Assembly of Superparamagnets: Review

Predicting the Self-Assembly of Superparamagnetic Colloids under Magnetic Fields.
Jordi Faraudo, Jordi S. Andreu, Carles Calero and Juan Camacho

Adv. Funct Materials 22, 3837 (2016)

a) Motion of colloids in a chain in an LD simulation; b) effective ellipsoid representing a chain of s colloids, which has anisotropic diffusion with different coefficients in the parallel and perpendicular directions. c) Map of magnetic potential energy of interaction between an imaginary colloid and a chain of five particles, all magnetized in the z-direction. The calculation corresponds to Γ = 40 and the magnetic energy is measured in units of k_BT. The dashed line indicates the regions at which the magnetic energy is equal (in absolute value) to the thermal energy. d) Coarse grain representation of the chain in panel (c) as employed in MagChain simulations in which the attractive region inside the dashed lines in panel (c) is replaced by a spherical region.

Science of Nanocrystals: Review

The surface science of nanocrystals.

Michael A. Boles, Daishun Ling, Taeghwan Hyeon & Dmitri V. Talapin
Nature Materials 15, 141 (2016)

Capping-layer structure.

Non-Boolean computing with nanomagnets for computer vision applications : Nature Nanotechnology : Nature Publishing Group

Non-Boolean computing with nanomagnets for computer vision applications.
Sanjukta Bhanja, D. K. Karunaratne, Ravi Panchumarthy, Srinath Rajaram, Sudeep Sarkar

Nature Nanotechnology 11, 177 (2016)

Stages in object recognition:a, Grey-scale satellite image of an urban area. b, Edge image with extracted edge segments from a. c, Traditional approach to solving a quadratic optimization process using a CMOS-based arithmetic and logic unit (ALU). d, Proposed method to solve the quadratic optimization process using a magnetic coprocessor. e, Salient edge segments identified from b using the method in c. f, Objects identified using salient edges obtained from e.

Colloidal crystals assemblies: Review

Assembly and phase transitions of colloidal crystals.

Bo Li, Di Zhou, Yilong Han

Nature Reviews Materials 1, 15011 (2016)

Phase diagrams of monodispersed colloids.

Nanomagnonics around the corner

Spintronics: Nanomagnonics around the corner

Dirk Grundler

Nature Nanotechnology 11, 407 (2016)

Reconfigurable magnonic conduits realized in domain walls: a, Spin wave of wavevector k propagating in a domain wall between two magnetic domains (top view). Spins precess at their given position (red arrows); electrons do not flow. The white arrows indicate magnetization vectors, M. b, A magnetic field, H, shifts the spin-wave nanochannel because a domain of magnetization, M, grows at the expense of the other domain. Magnetic volume charges are indicated by plus and minus signs.

Tunable exchange bias in dilute magnetic alloys – chiral spin glasses

Tunable exchange bias in dilute magnetic alloys – chiral spin glasses

Matthias Hudl, Roland Mathieu and Per Nordblad

Scientific Reports 6, 19964 (2016)

(a) The central part of M vs. H loops after cooling the sample in H_FC to 5 K, and measure the hysteresis loop on decreasing the field to – H_FC and back to +H_FC. The insets show the field dependence of the parameter H_sw1, H_sw2, (right) and ΔM (left) in the H_FC range 1 to 9 T. (b) Full hysteresis loops measured at 5 K from 0 to 14, 14 to −14 and then back +14 T. The inset shows the central part of the loop and the fields H_sw1 and H_sw2 are marked. The jump and definition of the excess magnetization, ΔM, is indicated in the main frame. (c,d) The central part of the hysteresis loops measured after field cooling (c) and zero field cooling (d) in fields up to 5 T at 5 K. The arrows indicate the initial field sweep direction. (Red loops- positive initial fields, blue loops - negative initial fields).