Spinel-structured compounds serve as prototypical examples of highly frustrated systems and are promising candidates for realizing the long-sought quantum spin liquid (QSL) state. However, structural disorder is inevitable in many real QSL candidates and its impact remains a topic of intense debate. In this work, we conduct comprehensive investigations on ${\mathrm{CuGa}}_2{\mathrm{O}}_4$, a spinel compound with significant structural disorder, focusing on its thermodynamic properties and spectroscopic behaviors. No long-range magnetic order is observed down to $\sim 80$ mK, as evidenced by magnetic susceptibility, specific-heat, and elastic neutron scattering measurements. More intriguingly, inelastic neutron scattering experiments reveal a broad gapless continuum of magnetic excitations around the Brillouin zone boundary, resembling the magnetic excitation spectra expected for a QSL. Nevertheless, a spin-freezing transition at $T_{\mathrm{f}}\approx 0.88$ K is identified from the cusp in the dc susceptibility curves, where a bifurcation between zero-field-cooling and field-cooling curves occurs. Furthermore, ac susceptibility measurements show a peak close to $T_{\mathrm{f}}$ at low frequency, which shifts to higher temperature with increasing frequency. These results show that ${\mathrm{CuGa}}_2{\mathrm{O}}_4$ has a spin-glass ground state, consistent with the establishment of short-range order inferred from the specific-heat measurements. Collectively, these results illustrate the crucial role of disorder in defining the excitation spectrum out of the disordered ground state. Our findings shed light onto the broader class of ${AB}_2{\mathrm{O}}_4$ spinels and advance our understanding of the spin dynamics in magnetically disordered systems.

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• Frustrated magnetism
• Magnetic susceptibility
• Magnetism
• Quantum spin liquid
• Specific heat
• Single crystal materials
• Spin glasses
• Strongly correlated systems
• Neutron scattering