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Magnetic Interaction between Surface-Engineered Rare-Earth Atomic Spins

Chiung-Yuan Lin1, Jheng-Lian Li1,2, Yao-Hsien Hsieh1, Keng-Liang Ou2,3, and B. A. Jones4

  • 1Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu, Taiwan
  • 2Research Center for Biomedical Devices, Taipei Medical University, Taipei, Taiwan
  • 3College of Oral Medicine, Taipei Medical University, Taipei, Taiwan
  • 4IBM Almaden Research Center, San Jose, California 95120-6099, USA

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Phys. Rev. X 2, 021012 – Published 22 June, 2012Erratum Phys. Rev. X 2, 039902 (2012)

DOI: https://doi.org/10.1103/PhysRevX.2.021012

Abstract

We report the ab-initio study of rare-earth adatoms (Gd) on an insulating surface. This surface is of interest because of previous studies by scanning tunneling microscopy showing spin excitations of transition-metal adatoms. The present work is the first study of rare-earth spin-coupled adatoms, as well as the geometry effect of spin coupling and the underlying mechanism of ferromagnetic coupling. The exchange coupling between Gd atoms on the surface is calculated to be antiferromagnetic in a linear geometry and ferromagnetic in a diagonal geometry. We also find that the Gd dimers in these two geometries are similar to the nearest-neighbor and the next-nearest-neighbor Gd atoms in GdN bulk. We analyze how much direct exchange, superexchange, and Ruderman-Kittel-Kasuya-Yosida interactions contribute to the exchange coupling for both geometries by additional first-principles calculations of related model systems.

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20 July, 2012

Erratum

Publisher’s Note: Magnetic Interaction between Surface-Engineered Rare-Earth Atomic Spins [Phys. Rev. X 2, 021012 (2012)]

Chiung-Yuan Lin, Jheng-Lian Li, Yao-Hsien Hsieh, Keng-Liang Ou, and B. A. Jones
Phys. Rev. X 2, 039902 (2012)

Popular Summary

Binary encoding based on controlled orientations of magnetic moments of the tiny domains of magnetic materials has been the scientific foundation for magnetism-based data-storage technologies. Bringing the scale of control and manipulation to the single-atom level points to a tantalizing future of computer circuits and data-storage devices that could be built to microscopic scales. Very recently, logic operations entirely based on engineered atomic magnetism and a single magnetic storage bit composed of only twelve iron atoms have been made possible by atomic-manipulation techniques derived from the landmark invention in the late 1980s of scanning tunneling microscopes (STM). To experimental progress of this kind, computer simulations based on fundamental physical principles of microscopic systems are indispensable: They reveal the detailed local geometries, charges, and the physical origin of interatomic magnetic interactions, information that is not available to the STM-based experiments and that can guide further engineering of atomic-scale magnetism. So far, all of the experimental and theoretical studies have concentrated on transition-metal magnetic atoms. Rare-earth atoms, while being naturally interesting and complex in the magnetic properties of their electrons, have not been explored in this context, however. In this theoretical paper, we study, for the first time and comprehensively, the magnetic interactions between pairs of rare-earth atoms adsorbed on a surface, opening new ground for atomic-scale magnetism.

Our approach starts from accurate and revealing density-functional calculations of the rare-earth atom Gd on a CuN surface. Gd has a half-filled 4f electron shell, and is expected, therefore, to exhibit electronic excitations that originate from pure spin coupling and that are without magnetic anisotropy in an STM measurement. The surface, CuN, is one commonly used in STM studies and acts both as an insulator and as a medium of superexchange between adsorbed Gd atoms. What we find is interesting and offers potential for multistage spin manipulations. The magnetic coupling between a dimer of Gd atoms on the CuN surface can actually be tuned from antiferromagnetic (which tends to turn the spins on the two atoms opposite in their orientations) to ferromagnetic (which tends to align the two spins), by orienting the dimer differently with respect to the nitrogen atoms. By devising a new method of decomposing the overall magnetic coupling into a number of sources and quantitatively identifying each contribution, we have also understood the precise nature of the mechanisms underlying the dimer-orientation-dependent antiferromagnetic and ferromagnetic couplings. The methodology and the fundamental understanding should have an impact beyond this first-studied case of atomic-scale rare-earth magnetism.

Article Text

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Outline

Information

Phys. Rev. X 2, 021012– Published 22 June, 2012
  • Received 9 March 2012
  • Corrected 20 July 2012
Article part of CHORUS
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This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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