Ab initio investigation of magnetic interactions in the frustrated triangular magnet NiGa2 S4

Physical Review B - Condensed Matter and Materials Physics

Volumn 76, Issue 14, 2007, Pages

  Mazin, I I ^a  

^a NAVAL RESEARCH LABORATORY   (United States)

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EID: 35348867374     PISSN: 10980121     EISSN: 1550235X     Source Type: Journal    
DOI: 10.1103/PhysRevB.76.140406     Document Type: Article

References (16)

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11. A recent paper [K. Takubo, T. Mizokawa, J.-Y. Son, Y. Nambu, K. Onuma H. Tonomura, S. Nakatsuji, and Y. Maeno Phys. Rev. Lett. PRLTAO 0031-9007 10.1103/PhysRevLett.99.037203 99, 037203, (2007)]
12. reported semiempirical cluster calculations and concluded, similar to our finding, that the third neighbor hopping is anomalously large. They interpreted that as coming from direct S-S overlap. Our calculations do not support this interpretation. First of all, we have observed exactly the same tendency, anomalously large third neighbor hopping, in isostructural oxides such as Nax CoO2, although direct O-O overlap should be much smaller than S-S. Second, as one can see from Fig. 4, in the approximation employed by Takubo, the nearest neighbor effective hopping is t1 ∼ t pdσ 2 (tppσ + tppπ) 2, the next hopping is t2 ∼ t pdσ 2 tppπ, and the third hopping is t3 ∼ t pdσ 2 (t ppσ ′ + t ppπ ′) 2 (where tpp corresponds to the shorter S-S bond and t pp ′ to the longer one. Using Andersen's and Harrison's canonical scalings, we have t pp ′ tpp (3.212 3.626) 3 0.7, and t ppσ ′ t ppπ ′ 2. This suggests that t3 t2 (2 3) t1. This is obviously incorrect and indicates that (a) the hopping parameters assumed by Takubo do not agree with the LDA ones and (b) particularly in the nearest neighbor hopping, other, more complex paths, such as Ni-S-Ga-S-Ni, play a very important role.
13. M. D. Johannes, I. I. Mazin, and D. J. Singh, Phys. Rev. B PRBMDO 0163-1829 10.1103/PhysRevB.71.214410 71, 214410 (2005).
14. See, e.g., E. V. Nagaev, Magnets with Complex Exchange Interactions (Nauka, Moscow, 1988).
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16. I. I. Mazin, O. K. Andersen, O. Jepsen, A. Yamasaki, and M. D. Johannes, (unpublished).