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Spin fluctuations and 3D itinerant magnetism in Na x CoO 2 : Slave‐boson mean‐field study
Author(s) -
Tang HuaiBao,
Li Guang,
Sun Jin,
Ma YongQing
Publication year - 2012
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201147435
Subject(s) - condensed matter physics , antiferromagnetism , physics , magnetism , ferromagnetism , slave boson , van hove singularity , hexagonal lattice , coulomb , hubbard model , heisenberg model , fermi level , quantum mechanics , superconductivity , electron
The in‐plane ferromagnetic (FM) fluctuations and three‐dimensional (3D) itinerant magnetism on the 3D triangular lattice of Na x CoO 2 are studied based on a single‐band Hubbard model using the Kotliar–Ruckenstein (KR) slave‐boson mean‐field (SBMF) technique. By analyzing the instabilities of the FM and layer‐type antiferromagnetic (AFM) susceptibilities, the in‐plane FM fluctuations in Na x CoO 2 with x < 0.63 are identified as the effects of both the strong Coulomb repulsion and the frustration on the Co ion triangular lattice. The saddle‐point solutions suggest that the experimental layer‐type AFM state is favorable for x > 0.75 due to the band top edge van Hove singularity arising from the next‐nearest‐neighbor (NNN) hopping. We also discuss the potential connection between the Curie–Weiss metallic behavior and the crossover from the weak FM phase to the layer‐type AFM phase at 0.63 < x < 0.75. Our results reveal the crucial role of the modified effects of the Coulomb interactions with doping x .