Quantum fluctuations in low-spin $(S=\frac{1}{2})$ systems make them potential materials to investigate various intriguing field-induced quantum phenomena. In this context, rare-earth $\left(4f\right)$-based effective spin $(J_{\mathrm{eff}}=\frac{1}{2})$ systems with localized magnetic moments and low energy scales offer an advantage of low critical fields and provide access to probe the complete magnetic phase diagram. Here, we present inelastic neutron scattering (INS) data to understand the crystal field (CF) scheme of the previously established $J_{\mathrm{eff}}=\frac{1}{2}$ antiferromagnet ${\mathrm{NdVO}}_4$, along with low-temperature magnetization and heat capacity measurements to construct the complete magnetic phase diagram. Our INS data validate the presence of the $J_{\mathrm{eff}}=\frac{1}{2}$ state at low temperatures with the ground and first excited CF state separated by an energy of 140 K. Furthermore, it yields a unique CF scheme where the excitation corresponding to the highest (fourth) CF state is observed via transitions involving the first and second excited states. Magnetic and heat capacity measurements yield the presence of a field-induced first-order spin-flop transition within the second-order antiferromagnetic (AFM) state. Magnetic phase diagrams constructed using the field-dependent magnetization and magnetic heat capacity reveal a continuous transformation from AFM to spin-flop state with a critical field of $H_{\mathrm{sf}}\sim 1.4\mathrm{T}$. The presence of quantum fluctuations near $H_{\mathrm{sf}}$ are evident from the V-shaped region in entropy contours indicating the presence of accumulated entropy.

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• Critical phenomena
• Crystal-field excitations
• Magnetocaloric effect
• Quantum phase transitions
• Rare-earth magnetic materials
• Inelastic neutron scattering
• Magnetization measurements
• Specific heat measurements