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Single Crystal 31P NMR Studies of the Frustrated Square Lattice Compound Pb2(VO)(PO4)2 | | R. Nath
; Y. Furukawa
; F. Borsa
; E. E. Kaul
; M. Baenitz
; C. Geibel
; D. C. Johnston
; | | Date: |
18 Sep 2009 | | Abstract: | The static and dynamic properties of V^{4+} spins (S = 1/2) in the frustrated
square lattice compound Pb2(VO)(PO4)2 were investigated by means of magnetic
susceptibility chi and 31P nuclear magnetic resonance (NMR) shift (K) and 31P
nuclear spin-lattice relaxation rate 1/T1 measurements on a single crystal.
This compound exhibits long-range antiferromagnetic order below TN simeq 3.65
K. NMR spectra above TN show two distinct lines corresponding to two
inequivalent P sites present in the crystal structure. The observed asymmetry
in hyperfine coupling constant for the in-plane (P1) P site directly points
towards a distortion in the square lattice at the microscopic level, consistent
with the monoclinic crystal structure. The nearest- and next-nearest-neighbor
exchange couplings were estimated by fitting K versus temperature T by a high
temperature series expansion for the spin susceptibility of the frustrated
square lattice to be J1/kB = (-5.4 pm 0.5) K (ferromagnetic) and J2/kB = (9.3
pm 0.6) K (antiferromagnetic), respectively. 1/(T1 T chi) is almost
T-independent at high temperatures due to random fluctuation of spin moments.
Below 20 K, the compound shows an enhancement of 1/(T1 T chi) which arises from
a growth of antiferromagnetic spin correlations above TN. Below TN, the NMR
spectrum for the P1 site splits into two satellites and the spacing between
them increases monotonically with decreasing T which is direct evidence of a
columnar antiferromagnetic ordering that is consistent with expectation from
the J2/J1 simeq -1.72 ratio. The critical exponent beta = 0.25 pm 0.02
estimated from the temperature dependence of sublattice magnetization measured
by 31P NMR at 11.13 MHz is close to the value (0.231) predicted for the
two-dimensional XY model. | | Source: | arXiv, 0909.3536 | | Services: | Forum | Review | PDF | Favorites | |
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