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

BaCdVO(PO$_{4})_{2}$ is a spin $S = $ 1/2 frustrated square-lattice compound with a nearest-neighbor exchange coupling $J_{1} = -$3.62 K and a next-nearest-neighbor exchange coupling $J_{2} = $ 3.18 K yielding \textbar $J_{2}$/$J_{1}$\textbar $=$ 0.88. A transition to an antiferromagnetic (AFM) ground state occurs below a temperature $T_{\mathrm{N}} = $ 1.0 K under ambient pressure $p$. Based on the $J_{2}$/$J_{1}$ ratio, the system is located close to the disordered ground state regime of the phase diagram. We carried out $^{31}$P-NMR measurements under high $p$ up to 1.88 GPa, and at low temperatures $T$ down to 100 mK, to investigate the effects of $p$ on the magnetic properties of the system. We established the first $H$--$p$--$T$ phase diagram for this system. With increasing $p$, the magnetization saturation field is suppressed from $H_{\mathrm{S}} = $ 4.2 T at ambient $p$ to $H_{\mathrm{S}} = $ 0.55 T at $p = $ 1.88 GPa and \textbar $J_{2}$/$J_{1}$\textbar decreases to 0.62 at $p = $ 1.45 GPa, thus moving towards the disordered region of the phase diagram.