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DESCRIPTION:Oliver Pieper \, Helmholtz- Zentrum Berlin\n\nCaV 2 O 4 is a quasi-one dimensional spin-1 Heisenberg antiferrom
agnet. The magnetism arises from the partially filled t 2g- l
evels of the V 3+- ions\, which in addition give an orbital d
egree of freedom to the system. In contrast to the isovalent vanadium spin
el compounds\, the low dimensionality in CaV 2 O 4 already arises from the crystal structure. It contains weakly coupled d
ouble-chains of edge-sharing VO 6 octahedra\, where the parti
cular octahedral staggering creates a zigzag-like arrangement of the vanad
ium ions. This in return gives rise to strong magnetic direct exchange int
eractions between nearest and next nearest neighbor vanadium ions and to g
eometrical frustration. However\, the strength of the exchange interaction
s is strongly influenced by the particular occupation of the t 2g- <
/sub> orbitals. Depending on the type and degree of octahedral distortion\
, the system can be interpreted as a frustrated Haldane chain or a spin-1
ladder. \nWe have used single crystal neutron diffraction and neutron spe
ctroscopy to determine the spin structure as well as the complex excitatio
n spectrum of CaV 2 O 4 . The results are analyz
ed theoretically and from this the leading exchange paths are deduced and
discussed in terms of orbital ordering.\n
DTSTART:20100128T210000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Orbital ordering in CaV 2 O 4 : A neutron
scattering study
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