Two- and three-dimensional magnetic correlations in the spin-1/2 square-lattice system Zn2VO(PO4)2

The magnetic correlations in the quasi-two dimensional spin-1/2 square-lattice system Zn2VO(PO4)2 have been investigated by neutron diffraction technique. A long-range antiferromagnetic (AFM) ordering below 3.75 K (TN) has been observed with a reduced moment of 0.66(2) {\mu}B per V ion at 1.5 K. In a given ab plane, the AFM spin arrangement is N\'eel type and the AFM layers are coupled ferromagnetically along the c axis. Remarkably, we have observed a pure 2D short-range AFM ordering in the ab plane above TN. Interestingly, the coexistence of diffuse magnetic scattering and three dimensional antiferromagnetic Bragg peaks has been found below TN, indicating the presence of spin-waves as confirmed by our calculation using the linear spin-wave theory. The observed results are discussed in the light of existing theory for a two-dimensional spin-1/2 square-lattice system.
Comment: 19 PAGES, 8 FIGURES, Accepted for publication in Physical Review B 2010