Two-dimensional magnetism and spin-size effect in the S = 1 triangular antiferromagnet NiGa2S4

Yusuke Nambu, Satoru Nakatsuji

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11 Citations (Scopus)


The triangular antiferromagnet is one of the most fundamental systems of geometrically frustrated magnets. NiGa2S4 is a layered chalcogenide compound with an equilateral triangular lattice, and it is a prime candidate for an S = 1 triangular antiferromagnet. Here we focus on low temperature magnetism in NiGa2S4, where quasi-static spins develop a spin-wave-like mode without forming any long-range ordering. We have studied low temperature magnetism of both polycrystalline samples and single crystals of Ni1 - xAxGa2S4 (A = Mn, Fe, Co, and Zn). A scaling law with a single energy scale of the Weiss temperature is found as an impurity effect and a hydrostatic pressure effect, providing evidence that it is in-plane interactions in the two-dimensional NiS2 plane that drive the critical slowing down to the viscous spin liquid state at T* = 8.5K and the spin-wave-like excitations of NiGa2S4 that emerge below T ∼ 3K. Furthermore, we find spin-size dependent impurity effects in the temperature dependence of the specific heat of Ni1 - xAxGa2S4. Even with a high impurity content, Zn2+ (S = 0) and Fe2+ (S = 2) substituted systems with weak XY anisotropy and integral spins retain the quadratic temperature dependence of the magnetic specific heat like pure NiGa2S4. A spin glass-like phase, on the other hand, emerges at low temperatures with the substitution of magnetic impurities with half-odd integer spins: Ising Co2 + (S = 32) and weak XYMn2 + S = 52) spins. This indicates that an integer size of spins is important for stabilizing the two-dimensional spin-wave-like behavior, and the unconventional spin state of NiGa 2S4 at low temperatures is distinct from a canonical spin glass.

Original languageEnglish
Article number164202
JournalJournal of Physics Condensed Matter
Issue number16
Publication statusPublished - 2011 Apr 27
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics


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