  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.
