Single-crystal 31P NMR studies of the frustrated square-lattice compound Pb2(VO)(PO4)2

Nath, R. ; Furukawa, Y. ; Borsa, F. ; Kaul, E. E. ; Baenitz, M. ; Geibel, C. ; Johnston, D. C. (2009) Single-crystal 31P NMR studies of the frustrated square-lattice compound Pb2(VO)(PO4)2 Physical Review B , 80 (21). 214430_1-214430_10. ISSN 1098-0121

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Official URL: http://prb.aps.org/abstract/PRB/v80/i21/e214430

Related URL: http://dx.doi.org/10.1103/PhysRevB.80.214430

Abstract

The static and dynamic properties of V4+ spins (S=1/2) in the frustrated square-lattice compound Pb2(VO)(PO4)2 were investigated by means of magnetic susceptibility χ 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≃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 toward 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±0.5) K (ferromagnetic) and J2/kB=(9.3±0.6) K (antiferromagnetic), respectively. 1/(T1Tχ) is almost T independent at high temperatures due to random fluctuation of spin moments. Below 20 K, the compound shows an enhancement of 1/(T1Tχ) which arises from a growth of antiferromagnetic spin correlations above TN. Below TN and for the field applied along the c axis, the NMR spectrum for the P1 site splits into two satellites and the spacing between them increases monotonically with decreasing T which is a direct evidence of a columnar antiferromagnetic ordering with spins lying in the ab plane. This type of magnetic ordering is consistent with expectation from the J2/J1≃−1.72 ratio. The critical exponent β=0.25±0.02 estimated from the temperature dependence of the sublattice magnetization as measured by 31P NMR at 11.13 MHz is close to the value (0.231) predicted for the two-dimensional XY model.

Item Type:Article
Source:Copyright of this article belongs to The American Physical Society.
ID Code:95679
Deposited On:20 Nov 2012 11:16
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