Information Transfer by Vector Spin Chirality in Finite Magnetic Chains

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Information Transfer by Vector Spin Chirality in Finite Magnetic Chains

Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten von Bergmann, André Kubetzka, and Roland Wiesendanger

Phys. Rev. Lett. 108, 197204 – Published 7 May 2012

See Viewpoint: Pushing Bits Through a Spin Wire

Abstract

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin spiral in finite individual bi-atomic Fe chains on the $(5 \times 1) - Ir (001)$ surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of nanometers away, suggesting a new way of transmitting information about the state of magnetic objects on the nanoscale.

Received 29 November 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.197204

Viewpoint

Pushing Bits Through a Spin Wire

Published 7 May 2012

Short chains of iron atoms deposited on a metal surface could be used to transmit bits of magnetic information.

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Authors & Affiliations

Matthias Menzel¹, Yuriy Mokrousov², Robert Wieser¹, Jessica E. Bickel¹, Elena Vedmedenko¹, Stefan Blügel², Stefan Heinze³, Kirsten von Bergmann¹, André Kubetzka¹, and Roland Wiesendanger¹

¹Institut für Angewandte Physik, Universität Hamburg, Jungiusstr. 11, 20355 Hamburg, Germany
²Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany
³Institut für Theoretische Physik und Astrophysik, Christian-Albrecht-Universität zu Kiel, Leibnizstr. 15, 24098 Kiel, Germany

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Issue

Vol. 108, Iss. 19 — 11 May 2012

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Images

Figure 1
Schematic representation of the investigated sample system and the experimental setup. The STM image in the front shows the atomically resolved ( $5 \times 1$ )-reconstructed Ir(001) surface (measurement parameters: $U = - 2 mV$ , $I = 40 nA$ , room temperature). Fe atoms deposited at room temperature form bi-atomic chains in the trenches of the reconstruction (ball model), which appear as a single strand in an STM image as shown in the overlaid image at the top (measurement parameters: $U = + 400 mV$ , $I = 5 nA$ , $T = 8 K$ ). The experimental setup allows to apply magnetic fields perpendicular to the sample surface, i.e., along the $z$ axis [10]. To investigate the magnetic order of the Fe chains we use spin-polarized STM with magnetic tips.Reuse & Permissions
Figure 2
SPSTM measurements of Fe chains on Ir(001). (a) and (b) Typical sample area of $30 \times 30 {nm}^{2}$ measured with an Fe-coated W tip without and with an applied external magnetic field of $B = + 2 T$ perpendicular to the sample surface, respectively, (constant current images colorized with simultaneously acquired $d I / d U$ maps, measurement parameters: $U = + 500 mV$ , $I = 5 nA$ , $T = 8 K$ ). (c) Topographic line profiles of the same Fe chain at $B = 0 T$ and $B = \pm 2 T$ measured with a Cr-coated tip. The insets show schematically the tip magnetization and how a 120° spin spiral, which is inverting in opposite fields, could explain the experimental results.Reuse & Permissions
Figure 3
DFT calculations and comparison to experimental findings. Spin-spiral dispersion from first-principles calculations: contributions from Heisenberg exchange (blue dots) and Dzyaloshinskii-Moriya interaction (black dots) and their sum (red dots). The lines represent fits to the calculations with an extended Heisenberg model and the dashed blue line is the Heisenberg exchange dispersion of a freestanding bi-atomic Fe chain. Inset: comparison of a simulated SPSTM image of a 120° spin spiral (gray scale inset; 5 Å above the surface, 50% spin polarization of the tip) with experimental data (color; constant current image, measurement parameters: $U = + 300 mV$ , $I = 5 nA$ , $T = 8 K$ ).Reuse & Permissions
Figure 4
Monte-Carlo simulations for a 30 atom long chain. (a) Temperature dependence of $M_{z}$ for different external magnetic fields applied along the $z$ axis. Upper inset depicts the temperature dependence of the normalized chiral and scalar order parameters as function of temperature. Lower inset displays the distribution of angles between nearest neighbor spins along the chain (the color of the lines corresponds to the temperature of the system given by the circle of the corresponding color below). (b) Laterally resolved time-averaged magnetization for two different temperatures at $B = + 2 T$ . (c) Three-dimensional representation of magnetization components of every atom for $T = 8 K$ and $B = + 2 T$ .Reuse & Permissions
Figure 5
SPSTM measurement of an isolated Fe chain (left) and an Fe chain directly connected to a ferromagnetic Co chain (center) taken at $B = 0 T$ with a Cr bulk tip ( $50 \times 12.5 {nm}^{2}$ constant current image, colorized with $d I / d U$ -map, measurement parameters: $U = + 500 mV$ , $I = 2 nA$ , $T = 8 K$ ). As seen in both the image and the line profiles below, the isolated Fe chain appears featureless while the one attached to the Co shows the periodicity indicative of spin-spiral order.Reuse & Permissions

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