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Paramagnetic electron-nuclear spin entanglement in HoCo2Zn20

Takafumi Kitazawa1,*,†, Yasuyuki Shimura2, Takahiro Onimaru2, Shun Tsuchida3, Katsunori Kubo1, Yoshinori Haga1, Hironori Sakai1, Yoshifumi Tokiwa1, Shinsaku Kambe1 et al.

Yo Tokunaga1

  • *Contact author: kitazawa.takafumi@phys.sci.hokudai.ac.jp
  • †Present address: Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.
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Phys. Rev. Research 8, 023009 – Published 2 April, 2026

DOI: https://doi.org/10.1103/bzvk-grrv

Abstract

We investigated electron-nuclear spin entanglement in the paramagnetic ground state of the Ho-based cubic compound HoCo2Zn20. From analyses of magnetization and specific heat data, we determined the cubic crystalline electric field (CEF) parameters, the magnetic exchange constant, and the hyperfine coupling constant between the 4f magnetic moment and the Ho165 nuclear spin. Our results show that the Γ5 CEF ground state is split by the hyperfine coupling, with an energy width of 1.3 K at 0 T, and that the true paramagnetic ground state is a quasisextet arising primarily from entanglement between the f-electron effective spin S=1 and the Ho165 nuclear spin I=7/2. We further demonstrate that, depending on the CEF parameters, the paramagnetic ground state can switch to an electron-nuclear coupled dectet. These findings underscore the importance of accurately identifying the electron-nuclear level scheme for understanding the low-temperature properties of rare-earth compounds containing spin-active nuclei.

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Phys. Rev. Research 8, 023009– Published 2 April, 2026
  • Received 1 October 2025
  • Accepted 17 February 2026
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