Zero-field magnetic resonance of cobalt ion pairs in ZnO nanocrystals

D. Marin, S. K. Tiwari, S. Bertaina, and A. Savoyant
Phys. Rev. B 105, 035424 – Published 21 January 2022
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Abstract

Cobalt-doped ZnO nanoparticles (NPs) with different Co concentrations are investigated by means of X- and Q-band electron spin resonance (ESR) near liquid-helium temperature in both parallel and perpendicular modes. The high crystal quality of the NPs allows for the hyperfine-structure resolution within the single Co2+ ions' ESR powder spectra. Depending on cobalt concentration, common additional weak ESR lines are detected which are here demonstrated to arise from some Co2+ high-spin pairs with a distance of about 4–6 Å. ESR simulations show that these 3/2 spin pairs are weakly coupled by an isotropic Heisenberg Hamiltonian with either ferromagnetic or antiferromagnetic J coupling constants, almost identical to those previously detected in bulk and microwire ZnO:Co. The presence of substantial (axial) single-ion anisotropy in ZnO:Co makes the different pairs' resonance positions strongly depending on the J value. For resonance frequency ν in the microwave range, four cobalt pairs can satisfy the condition |J|hν/3 to resonate at almost zero magnetic field. Such near-zero-field transitions notably resonate in the parallel ESR mode, which is the signature of the gapped nonlinear Zeeman effect, which is of particular interest for highly stable atomic-clock transitions.

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  • Received 9 September 2021
  • Revised 8 November 2021
  • Accepted 6 January 2022

DOI:https://doi.org/10.1103/PhysRevB.105.035424

©2022 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

D. Marin1, S. K. Tiwari2, S. Bertaina1, and A. Savoyant1

  • 1Aix-Marseille Université, CNRS, IM2NP UMR 7334, 13397 Marseille Cedex 20, France
  • 2Department of Physics and Materials Science, Jaypee University of Information Technology, Waknaghat Solan, Himachal Pradesh 173234, India

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Issue

Vol. 105, Iss. 3 — 15 January 2022

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