16 research outputs found
Frustrated square lattice with spatial anisotropy: crystal structure and magnetic properties of PbZnVO(PO4)2
Crystal structure and magnetic properties of the layered vanadium phosphate
PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and
specific heat measurements, as well as band structure calculations. The
compound resembles AA'VO(PO4)2 vanadium phosphates and fits to the extended
frustrated square lattice model with the couplings J(1), J(1)' between
nearest-neighbors and J(2), J(2)' between next-nearest-neighbors. The
temperature dependence of the magnetization yields estimates of averaged
nearest-neighbor and next-nearest-neighbor couplings, J(1) ~ -5.2 K and J(2) ~
10.0 K, respectively. The effective frustration ratio alpha=J(2)/J(1) amounts
to -1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2.
Specific heat data support the estimates of J(1) and J(2) and indicate a likely
magnetic ordering transition at 3.9 K. However, the averaged couplings
underestimate the saturation field, thus pointing to the spatial anisotropy of
the nearest-neighbor interactions. Band structure calculations confirm the
identification of ferromagnetic J(1), J(1)' and antiferromagnetic J(2), J(2)'
in PbZnVO(PO4)2 and yield J(1)'-J(1) ~ 1.1 K in excellent agreement with the
experimental value of 1.1 K, deduced from the difference between the expected
and experimentally measured saturation fields. Based on the comparison of
layered vanadium phosphates with different metal cations, we show that a
moderate spatial anisotropy of the frustrated square lattice has minor
influence on the thermodynamic properties of the model. We discuss relevant
geometrical parameters, controlling the exchange interactions in these
compounds, and propose a new route towards strongly frustrated square lattice
materials.Comment: 14 pages, 9 figures, 5 table
Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation
The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated
by means of X-ray powder diffraction, electron diffraction, magnetic
susceptibility measurements and band structure calculations. Its structure is
similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin
system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements
reveal a spin gap-like behavior with \Delta ~ 270 K and a spin singlet ground
state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a
system of weakly coupled dimers in perfect agreement with the experimental
data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the
spin system in layered vanadium oxides by cation substitution. Simple
correlations between the cation size, geometrical parameters and exchange
integrals for the MV(2)O(5)-type oxides are established and discussed.Comment: 8 pages, 7 figure
Frustrated spin-1/2 square lattice in the layered perovskite PbVO(3)
We report on the magnetic properties of the layered perovskite PbVO(3). The
results of magnetic susceptibility and specific heat measurements as well as
band structure calculations consistently suggest that the S=1/2 square lattice
of vanadium atoms in PbVO(3) is strongly frustrated due to
next-nearest-neighbor antiferromagnetic interactions. The ratio of
next-nearest-neighbor (J(2)) to nearest-neighbor (J(1)) exchange integrals is
estimated to be J(2)/J(1)\approx 0.2-0.4. Thus, PbVO(3) is within or close to
the critical region of the J(1)-J(2) frustrated square lattice. Supporting
this, no sign of long-range magnetic ordering was found down to 1.8 K.Comment: 4 pages, 4 figures, 2 table