Orbital and magnetic transitions in geometrically-frustrated vanadium spinels -- Monte Carlo study of an effective spin-orbital-lattice coupled model --

Abstract

We present our theoretical and numerical results on thermodynamic properties and the microscopic mechanism of two successive transitions in vanadium spinel oxides $A$V${}_2$O${}_4$ ($A$=Zn, Mg, or Cd) obtained by Monte Carlo calculations of an effective spin-orbital-lattice model in the strong correlation limit. Geometrical frustration in the pyrochlore lattice structure of V cations suppresses development of spin and orbital correlations, however, we find that the model exhibits two transitions at low temperatures. First, a discontinuous transition occurs with an orbital ordering assisted by the tetragonal Jahn-Teller distortion. The orbital order reduces the frustration in spin exchange interactions, and induces antiferromagnetic correlations in one-dimensional chains lying in the perpendicular planes to the tetragonal distortion. Secondly, at a lower temperature, a three-dimensional antiferromagnetic order sets in continuously, which is stabilized by the third-neighbor interaction among the one-dimensional antiferromagnetic chains. Thermal fluctuations are crucial to stabilize the collinear magnetic state by the order-by-disorder mechanism. The results well reproduce the experimental data such as transition temperatures, temperature dependence of the magnetic susceptibility, changes of the entropy at the transitions, and the magnetic ordering structure at low temperatures. Quantum fluctuation effect is also examined by the linear spin wave theory at zero temperature. The staggered moment in the ground state is found to be considerably reduced from saturated value, and reasonably agrees with the experimental data.

arXiv comment22 pages, 23 figures

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• Anisotropic pyrochlores and the global phase diagram of the checkerboard antiferromagnet
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• Homopolar bond formation in ZnV${}_2$O${}_4$ close to a metal-insulator transition
• Lattice gas description of pyrochlore and checkerboard antiferromagnets in a strong magnetic field
• Classical dimers and dimerized superstructure in orbitally degenerate honeycomb antiferromagnet
• Unusual superexchange pathways in a Ni triangular lattice of NiGa${}_2$S${}_4$ with negative charge-transfer energy
• Investigation of the Thermoelectric Properties of ZnV${}_2$O${}_4$ Compound in High Temperature Region
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• Structural transition and orbital glass physics in near itinerant CoV2O4
• Effective Hamiltonian for the Pyrochlore antiferromagnet: semiclassical derivation and degeneracy
• Magnons and a two-component spin gap in FeV2O4
• Magnetic Field Induced Transition in Vanadium Spinels
• Magnetic excitations in vanadium spinels
• Orbital Ordering in Fe${}_{1-x}$Mn${}_x$V${}_2$O${}_4$: A First Principles Study
• Electronic States and Possible Origin of the Orbital-Glass State in a Nearly Metallic Spinel Cobalt Vanadate: An X-ray Magnetic Circular Dichroism Study
• Spin Canting and Orbital Order in Spinel Vanadate Thin Films
• Density matrix approach to the orbital ordering in the spinel vanadates: A case study
• Limitations of unconstrained LSDA+$U$ calculations in predicting the electronic and magnetic ground state of a geometrically frustrated ZnV${}_2$O${}_4$ compound
• Charge ordering in the spinels AlV${}_2$O${}_4$ and LiV${}_2$O${}_4$
• The ground state phases of orbitally degenerate spinel oxides
• Large Magnetic Anisotropy and Magnetostriction in Thin Films of CoV${}_2$O${}_4$
• Orbital ordering and one-dimensional magnetic correlation in vanadium spinel oxides AV2O4 (A = Zn, Mg, or Cd)
• Suppression of Spin Frustration due to Orbital Selection
• Spin Frustration and Orbital Order in Vanadium Spinels
• Novel electronic states close to Mott transition in low-dimensional and frustrated systems
• Quantum Monte-Carlo study of magnetic ordering in ZnV2O4