The Magnetic Structure and Electronic Ground States of Mott Insulators GeV4S8 and GaV4S8

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• 作者：Helen M&uuml ; ller ; Winfried Kockelmann ; and Dirk Johrendt
• 刊名：Chemistry of Materials
• 出版年：2006
• 出版时间：April 18, 2006
• 年：2006
• 卷：18
• 期：8
• 页码：2174 - 2180
• 全文大小：306K
• 年卷期：v.18,no.8(April 18, 2006)
• ISSN：1520-5002

文摘

The ground states of magnetic Mott insulators GaV₄S₈ and GeV₄S₈ were calculated with full-potentialLAPW methods using the LDA + U approach. Both compounds undergo structural distortions fromcubic to rhombohedral (GaV₄S₈) or orthorhombic (GeV₄S₈) symmetry at low temperatures. GaV₄S₈ isferromagnetic below T_C = 10 K, whereas GeV₄S₈ shows antiferromagnetic order with T_N = 13 K. Thespin structure of GeV₄S₈ was determined by neutron diffraction and described in the magnetic spacegroup P_bmn2₁. The magnetic propagation vector is [¹/₂, ¹/₂, 0] relating to the cubic paramagnetic unitcell. The LDA + U calculations (U = 2 eV) confirm the magnetic insulating ground states for the firsttime with magnetic moments and energy gaps in very good agreement with the experimental data. Thismethod also reproduces the antiferromagnetic spin ordering of GeV₄S₈. The Jahn-Teller instability ofthe degenerated levels in the V₄ cluster MO drives the structural distortions, depending on the clusterelectron count. Our results show how the interplay between the electronic, lattice, and spin degrees offreedom of the V₄ cluster units determines the physical and structural properties of these highly correlatedtransition-metal sulfides.