Low Temperature $^{31}$P-NMR Study of the Frustrated Square-Lattice Compound BaCdVO(PO$_{4}$)$_{2}$

BaCdVO(PO$_{4})_{2}$ is known to be a S = $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ frustrated square-lattice (FSL) system with a ferromagnetic nearest neighbor exchange coupling J$_{1}\sim $ -3.36 K and an antiferromagnetic next nearest neighbor exchange coupling J$_{2}\sim $ 3.53 K. We have carried out $^{31}$P-NMR measurements at low temperatures down to 0.1 K to investigate magnetic properties of this compound from a microscopic point of view. $^{31}$P spin-lattice relaxation rates (1/T$_{1})$ measured at H = 0.8 T are almost independent of temperature above 2 K, show a peak at 1.05 K and become constant below 0.4 K. The temperature dependence of 1/T$_{1}$ indicates the existence of antiferromagnetic ordering at T$_{N}\sim $ 1.05 K which is also evidenced by the broadening of the NMR spectrum below that temperature. We will compare our NMR results with those of a similar FSL system, Pb$_{2}$VO(PO$_{4})_{2}$ and discuss the similarities and differences in the magnetic properties of these two systems.