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<p>NiI₂ and NiBr₂ are archetypal van der Waals (vdW) triangular-lattice multiferroics that host incommensurate helimagnetic order at the lowest temperatures and undergo a transition to collinear antiferromagnetic order upon heating. Focusing on NiBr₂, we reveal that both antiferromagnetic phases exhibit a pronounced sensitivity to hydrostatic pressure. The Néel temperature of the collinear phase increases steeply at ~20 K/GPa, reaching ~100 K at 3 GPa without any indication of saturation, whereas the helimagnetic phase is completely suppressed only above ~0.8 GPa. This behavior contrasts sharply with NiI₂, in which both helical and collinear phases are strengthened until a moderate pressure of ∼6 GPa, above which the helical phase instantly disappears. Ab initio calculations identify the second-nearest interlayer exchange interaction <i>j</i>₂′ as the primary driver stabilizing the collinear AFM phase in NiBr₂. In addition, the in-plane exchange ratio renders the helical order in NiBr₂ considerably more fragile, enabling its suppression under relatively small pressures. These results underscore the dominant role of interlayer interactions in governing the distinct pressure responses of the magnetic phases in NiBr₂ and NiI₂.</p>

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Opposite pressure effects on magnetic phase transitions in NiBr2

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月10日

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  • Parvez Ahmed Qureshi,
  • Krishna Kumar Pokhrel,
  • Jiří Prchal,
  • Subhasmita Ray,
  • Sergiu Arapan,
  • Karel Carva,
  • Vladimír Sechovský,
  • Jiří Pospíšil

摘要

NiI₂ and NiBr₂ are archetypal van der Waals (vdW) triangular-lattice multiferroics that host incommensurate helimagnetic order at the lowest temperatures and undergo a transition to collinear antiferromagnetic order upon heating. Focusing on NiBr₂, we reveal that both antiferromagnetic phases exhibit a pronounced sensitivity to hydrostatic pressure. The Néel temperature of the collinear phase increases steeply at ~20 K/GPa, reaching ~100 K at 3 GPa without any indication of saturation, whereas the helimagnetic phase is completely suppressed only above ~0.8 GPa. This behavior contrasts sharply with NiI₂, in which both helical and collinear phases are strengthened until a moderate pressure of ∼6 GPa, above which the helical phase instantly disappears. Ab initio calculations identify the second-nearest interlayer exchange interaction j₂′ as the primary driver stabilizing the collinear AFM phase in NiBr₂. In addition, the in-plane exchange ratio renders the helical order in NiBr₂ considerably more fragile, enabling its suppression under relatively small pressures. These results underscore the dominant role of interlayer interactions in governing the distinct pressure responses of the magnetic phases in NiBr₂ and NiI₂.